Embedded_AI/gcc-linaro-7.5.0-2019.12-x86_64_arm-linux-gnueabihf/arm-linux-gnueabihf/libc/usr/share/info/libc.info-4

This is libc.info, produced by makeinfo version 5.2 from libc.texinfo.

This file documents the GNU C Library.

   This is ‘The GNU C Library Reference Manual’, for version 2.25.

   Copyright © 1993–2017 Free Software Foundation, Inc.

   Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3 or
any later version published by the Free Software Foundation; with the
Invariant Sections being “Free Software Needs Free Documentation” and
“GNU Lesser General Public License”, the Front-Cover texts being “A GNU
Manual”, and with the Back-Cover Texts as in (a) below.  A copy of the
license is included in the section entitled "GNU Free Documentation
License".

   (a) The FSF’s Back-Cover Text is: “You have the freedom to copy and
modify this GNU manual.  Buying copies from the FSF supports it in
developing GNU and promoting software freedom.”
INFO-DIR-SECTION Software libraries
START-INFO-DIR-ENTRY
* Libc: (libc).                 C library.
END-INFO-DIR-ENTRY

INFO-DIR-SECTION GNU C library functions and macros
START-INFO-DIR-ENTRY
* a64l: (libc)Encode Binary Data.
* abort: (libc)Aborting a Program.
* abs: (libc)Absolute Value.
* accept: (libc)Accepting Connections.
* access: (libc)Testing File Access.
* acosf: (libc)Inverse Trig Functions.
* acoshf: (libc)Hyperbolic Functions.
* acosh: (libc)Hyperbolic Functions.
* acoshl: (libc)Hyperbolic Functions.
* acos: (libc)Inverse Trig Functions.
* acosl: (libc)Inverse Trig Functions.
* addmntent: (libc)mtab.
* addseverity: (libc)Adding Severity Classes.
* adjtime: (libc)High-Resolution Calendar.
* adjtimex: (libc)High-Resolution Calendar.
* aio_cancel64: (libc)Cancel AIO Operations.
* aio_cancel: (libc)Cancel AIO Operations.
* aio_error64: (libc)Status of AIO Operations.
* aio_error: (libc)Status of AIO Operations.
* aio_fsync64: (libc)Synchronizing AIO Operations.
* aio_fsync: (libc)Synchronizing AIO Operations.
* aio_init: (libc)Configuration of AIO.
* aio_read64: (libc)Asynchronous Reads/Writes.
* aio_read: (libc)Asynchronous Reads/Writes.
* aio_return64: (libc)Status of AIO Operations.
* aio_return: (libc)Status of AIO Operations.
* aio_suspend64: (libc)Synchronizing AIO Operations.
* aio_suspend: (libc)Synchronizing AIO Operations.
* aio_write64: (libc)Asynchronous Reads/Writes.
* aio_write: (libc)Asynchronous Reads/Writes.
* alarm: (libc)Setting an Alarm.
* aligned_alloc: (libc)Aligned Memory Blocks.
* alloca: (libc)Variable Size Automatic.
* alphasort64: (libc)Scanning Directory Content.
* alphasort: (libc)Scanning Directory Content.
* ALTWERASE: (libc)Local Modes.
* ARG_MAX: (libc)General Limits.
* argp_error: (libc)Argp Helper Functions.
* ARGP_ERR_UNKNOWN: (libc)Argp Parser Functions.
* argp_failure: (libc)Argp Helper Functions.
* argp_help: (libc)Argp Help.
* argp_parse: (libc)Argp.
* argp_state_help: (libc)Argp Helper Functions.
* argp_usage: (libc)Argp Helper Functions.
* argz_add: (libc)Argz Functions.
* argz_add_sep: (libc)Argz Functions.
* argz_append: (libc)Argz Functions.
* argz_count: (libc)Argz Functions.
* argz_create: (libc)Argz Functions.
* argz_create_sep: (libc)Argz Functions.
* argz_delete: (libc)Argz Functions.
* argz_extract: (libc)Argz Functions.
* argz_insert: (libc)Argz Functions.
* argz_next: (libc)Argz Functions.
* argz_replace: (libc)Argz Functions.
* argz_stringify: (libc)Argz Functions.
* asctime: (libc)Formatting Calendar Time.
* asctime_r: (libc)Formatting Calendar Time.
* asinf: (libc)Inverse Trig Functions.
* asinhf: (libc)Hyperbolic Functions.
* asinh: (libc)Hyperbolic Functions.
* asinhl: (libc)Hyperbolic Functions.
* asin: (libc)Inverse Trig Functions.
* asinl: (libc)Inverse Trig Functions.
* asprintf: (libc)Dynamic Output.
* assert: (libc)Consistency Checking.
* assert_perror: (libc)Consistency Checking.
* atan2f: (libc)Inverse Trig Functions.
* atan2: (libc)Inverse Trig Functions.
* atan2l: (libc)Inverse Trig Functions.
* atanf: (libc)Inverse Trig Functions.
* atanhf: (libc)Hyperbolic Functions.
* atanh: (libc)Hyperbolic Functions.
* atanhl: (libc)Hyperbolic Functions.
* atan: (libc)Inverse Trig Functions.
* atanl: (libc)Inverse Trig Functions.
* atexit: (libc)Cleanups on Exit.
* atof: (libc)Parsing of Floats.
* atoi: (libc)Parsing of Integers.
* atol: (libc)Parsing of Integers.
* atoll: (libc)Parsing of Integers.
* backtrace: (libc)Backtraces.
* backtrace_symbols_fd: (libc)Backtraces.
* backtrace_symbols: (libc)Backtraces.
* basename: (libc)Finding Tokens in a String.
* basename: (libc)Finding Tokens in a String.
* BC_BASE_MAX: (libc)Utility Limits.
* BC_DIM_MAX: (libc)Utility Limits.
* bcmp: (libc)String/Array Comparison.
* bcopy: (libc)Copying Strings and Arrays.
* BC_SCALE_MAX: (libc)Utility Limits.
* BC_STRING_MAX: (libc)Utility Limits.
* bind: (libc)Setting Address.
* bind_textdomain_codeset: (libc)Charset conversion in gettext.
* bindtextdomain: (libc)Locating gettext catalog.
* BRKINT: (libc)Input Modes.
* brk: (libc)Resizing the Data Segment.
* bsearch: (libc)Array Search Function.
* btowc: (libc)Converting a Character.
* BUFSIZ: (libc)Controlling Buffering.
* bzero: (libc)Copying Strings and Arrays.
* cabsf: (libc)Absolute Value.
* cabs: (libc)Absolute Value.
* cabsl: (libc)Absolute Value.
* cacosf: (libc)Inverse Trig Functions.
* cacoshf: (libc)Hyperbolic Functions.
* cacosh: (libc)Hyperbolic Functions.
* cacoshl: (libc)Hyperbolic Functions.
* cacos: (libc)Inverse Trig Functions.
* cacosl: (libc)Inverse Trig Functions.
* calloc: (libc)Allocating Cleared Space.
* canonicalize_file_name: (libc)Symbolic Links.
* canonicalizef: (libc)FP Bit Twiddling.
* canonicalize: (libc)FP Bit Twiddling.
* canonicalizel: (libc)FP Bit Twiddling.
* cargf: (libc)Operations on Complex.
* carg: (libc)Operations on Complex.
* cargl: (libc)Operations on Complex.
* casinf: (libc)Inverse Trig Functions.
* casinhf: (libc)Hyperbolic Functions.
* casinh: (libc)Hyperbolic Functions.
* casinhl: (libc)Hyperbolic Functions.
* casin: (libc)Inverse Trig Functions.
* casinl: (libc)Inverse Trig Functions.
* catanf: (libc)Inverse Trig Functions.
* catanhf: (libc)Hyperbolic Functions.
* catanh: (libc)Hyperbolic Functions.
* catanhl: (libc)Hyperbolic Functions.
* catan: (libc)Inverse Trig Functions.
* catanl: (libc)Inverse Trig Functions.
* catclose: (libc)The catgets Functions.
* catgets: (libc)The catgets Functions.
* catopen: (libc)The catgets Functions.
* cbc_crypt: (libc)DES Encryption.
* cbrtf: (libc)Exponents and Logarithms.
* cbrt: (libc)Exponents and Logarithms.
* cbrtl: (libc)Exponents and Logarithms.
* ccosf: (libc)Trig Functions.
* ccoshf: (libc)Hyperbolic Functions.
* ccosh: (libc)Hyperbolic Functions.
* ccoshl: (libc)Hyperbolic Functions.
* ccos: (libc)Trig Functions.
* ccosl: (libc)Trig Functions.
* CCTS_OFLOW: (libc)Control Modes.
* ceilf: (libc)Rounding Functions.
* ceil: (libc)Rounding Functions.
* ceill: (libc)Rounding Functions.
* cexpf: (libc)Exponents and Logarithms.
* cexp: (libc)Exponents and Logarithms.
* cexpl: (libc)Exponents and Logarithms.
* cfgetispeed: (libc)Line Speed.
* cfgetospeed: (libc)Line Speed.
* cfmakeraw: (libc)Noncanonical Input.
* cfree: (libc)Freeing after Malloc.
* cfsetispeed: (libc)Line Speed.
* cfsetospeed: (libc)Line Speed.
* cfsetspeed: (libc)Line Speed.
* chdir: (libc)Working Directory.
* CHILD_MAX: (libc)General Limits.
* chmod: (libc)Setting Permissions.
* chown: (libc)File Owner.
* CIGNORE: (libc)Control Modes.
* cimagf: (libc)Operations on Complex.
* cimag: (libc)Operations on Complex.
* cimagl: (libc)Operations on Complex.
* clearenv: (libc)Environment Access.
* clearerr: (libc)Error Recovery.
* clearerr_unlocked: (libc)Error Recovery.
* CLK_TCK: (libc)Processor Time.
* CLOCAL: (libc)Control Modes.
* clock: (libc)CPU Time.
* CLOCKS_PER_SEC: (libc)CPU Time.
* clog10f: (libc)Exponents and Logarithms.
* clog10: (libc)Exponents and Logarithms.
* clog10l: (libc)Exponents and Logarithms.
* clogf: (libc)Exponents and Logarithms.
* clog: (libc)Exponents and Logarithms.
* clogl: (libc)Exponents and Logarithms.
* closedir: (libc)Reading/Closing Directory.
* close: (libc)Opening and Closing Files.
* closelog: (libc)closelog.
* COLL_WEIGHTS_MAX: (libc)Utility Limits.
* _Complex_I: (libc)Complex Numbers.
* confstr: (libc)String Parameters.
* conjf: (libc)Operations on Complex.
* conj: (libc)Operations on Complex.
* conjl: (libc)Operations on Complex.
* connect: (libc)Connecting.
* copysignf: (libc)FP Bit Twiddling.
* copysign: (libc)FP Bit Twiddling.
* copysignl: (libc)FP Bit Twiddling.
* cosf: (libc)Trig Functions.
* coshf: (libc)Hyperbolic Functions.
* cosh: (libc)Hyperbolic Functions.
* coshl: (libc)Hyperbolic Functions.
* cos: (libc)Trig Functions.
* cosl: (libc)Trig Functions.
* cpowf: (libc)Exponents and Logarithms.
* cpow: (libc)Exponents and Logarithms.
* cpowl: (libc)Exponents and Logarithms.
* cprojf: (libc)Operations on Complex.
* cproj: (libc)Operations on Complex.
* cprojl: (libc)Operations on Complex.
* CPU_CLR: (libc)CPU Affinity.
* CPU_ISSET: (libc)CPU Affinity.
* CPU_SET: (libc)CPU Affinity.
* CPU_SETSIZE: (libc)CPU Affinity.
* CPU_ZERO: (libc)CPU Affinity.
* CREAD: (libc)Control Modes.
* crealf: (libc)Operations on Complex.
* creal: (libc)Operations on Complex.
* creall: (libc)Operations on Complex.
* creat64: (libc)Opening and Closing Files.
* creat: (libc)Opening and Closing Files.
* CRTS_IFLOW: (libc)Control Modes.
* crypt: (libc)crypt.
* crypt_r: (libc)crypt.
* CS5: (libc)Control Modes.
* CS6: (libc)Control Modes.
* CS7: (libc)Control Modes.
* CS8: (libc)Control Modes.
* csinf: (libc)Trig Functions.
* csinhf: (libc)Hyperbolic Functions.
* csinh: (libc)Hyperbolic Functions.
* csinhl: (libc)Hyperbolic Functions.
* csin: (libc)Trig Functions.
* csinl: (libc)Trig Functions.
* CSIZE: (libc)Control Modes.
* csqrtf: (libc)Exponents and Logarithms.
* csqrt: (libc)Exponents and Logarithms.
* csqrtl: (libc)Exponents and Logarithms.
* CSTOPB: (libc)Control Modes.
* ctanf: (libc)Trig Functions.
* ctanhf: (libc)Hyperbolic Functions.
* ctanh: (libc)Hyperbolic Functions.
* ctanhl: (libc)Hyperbolic Functions.
* ctan: (libc)Trig Functions.
* ctanl: (libc)Trig Functions.
* ctermid: (libc)Identifying the Terminal.
* ctime: (libc)Formatting Calendar Time.
* ctime_r: (libc)Formatting Calendar Time.
* cuserid: (libc)Who Logged In.
* dcgettext: (libc)Translation with gettext.
* dcngettext: (libc)Advanced gettext functions.
* DES_FAILED: (libc)DES Encryption.
* des_setparity: (libc)DES Encryption.
* dgettext: (libc)Translation with gettext.
* difftime: (libc)Elapsed Time.
* dirfd: (libc)Opening a Directory.
* dirname: (libc)Finding Tokens in a String.
* div: (libc)Integer Division.
* dngettext: (libc)Advanced gettext functions.
* drand48: (libc)SVID Random.
* drand48_r: (libc)SVID Random.
* dremf: (libc)Remainder Functions.
* drem: (libc)Remainder Functions.
* dreml: (libc)Remainder Functions.
* DTTOIF: (libc)Directory Entries.
* dup2: (libc)Duplicating Descriptors.
* dup: (libc)Duplicating Descriptors.
* E2BIG: (libc)Error Codes.
* EACCES: (libc)Error Codes.
* EADDRINUSE: (libc)Error Codes.
* EADDRNOTAVAIL: (libc)Error Codes.
* EADV: (libc)Error Codes.
* EAFNOSUPPORT: (libc)Error Codes.
* EAGAIN: (libc)Error Codes.
* EALREADY: (libc)Error Codes.
* EAUTH: (libc)Error Codes.
* EBACKGROUND: (libc)Error Codes.
* EBADE: (libc)Error Codes.
* EBADFD: (libc)Error Codes.
* EBADF: (libc)Error Codes.
* EBADMSG: (libc)Error Codes.
* EBADR: (libc)Error Codes.
* EBADRPC: (libc)Error Codes.
* EBADRQC: (libc)Error Codes.
* EBADSLT: (libc)Error Codes.
* EBFONT: (libc)Error Codes.
* EBUSY: (libc)Error Codes.
* ECANCELED: (libc)Error Codes.
* ecb_crypt: (libc)DES Encryption.
* ECHILD: (libc)Error Codes.
* ECHOCTL: (libc)Local Modes.
* ECHOE: (libc)Local Modes.
* ECHOKE: (libc)Local Modes.
* ECHOK: (libc)Local Modes.
* ECHO: (libc)Local Modes.
* ECHONL: (libc)Local Modes.
* ECHOPRT: (libc)Local Modes.
* ECHRNG: (libc)Error Codes.
* ECOMM: (libc)Error Codes.
* ECONNABORTED: (libc)Error Codes.
* ECONNREFUSED: (libc)Error Codes.
* ECONNRESET: (libc)Error Codes.
* ecvt: (libc)System V Number Conversion.
* ecvt_r: (libc)System V Number Conversion.
* EDEADLK: (libc)Error Codes.
* EDEADLOCK: (libc)Error Codes.
* EDESTADDRREQ: (libc)Error Codes.
* EDIED: (libc)Error Codes.
* ED: (libc)Error Codes.
* EDOM: (libc)Error Codes.
* EDOTDOT: (libc)Error Codes.
* EDQUOT: (libc)Error Codes.
* EEXIST: (libc)Error Codes.
* EFAULT: (libc)Error Codes.
* EFBIG: (libc)Error Codes.
* EFTYPE: (libc)Error Codes.
* EGRATUITOUS: (libc)Error Codes.
* EGREGIOUS: (libc)Error Codes.
* EHOSTDOWN: (libc)Error Codes.
* EHOSTUNREACH: (libc)Error Codes.
* EHWPOISON: (libc)Error Codes.
* EIDRM: (libc)Error Codes.
* EIEIO: (libc)Error Codes.
* EILSEQ: (libc)Error Codes.
* EINPROGRESS: (libc)Error Codes.
* EINTR: (libc)Error Codes.
* EINVAL: (libc)Error Codes.
* EIO: (libc)Error Codes.
* EISCONN: (libc)Error Codes.
* EISDIR: (libc)Error Codes.
* EISNAM: (libc)Error Codes.
* EKEYEXPIRED: (libc)Error Codes.
* EKEYREJECTED: (libc)Error Codes.
* EKEYREVOKED: (libc)Error Codes.
* EL2HLT: (libc)Error Codes.
* EL2NSYNC: (libc)Error Codes.
* EL3HLT: (libc)Error Codes.
* EL3RST: (libc)Error Codes.
* ELIBACC: (libc)Error Codes.
* ELIBBAD: (libc)Error Codes.
* ELIBEXEC: (libc)Error Codes.
* ELIBMAX: (libc)Error Codes.
* ELIBSCN: (libc)Error Codes.
* ELNRNG: (libc)Error Codes.
* ELOOP: (libc)Error Codes.
* EMEDIUMTYPE: (libc)Error Codes.
* EMFILE: (libc)Error Codes.
* EMLINK: (libc)Error Codes.
* EMSGSIZE: (libc)Error Codes.
* EMULTIHOP: (libc)Error Codes.
* ENAMETOOLONG: (libc)Error Codes.
* ENAVAIL: (libc)Error Codes.
* encrypt: (libc)DES Encryption.
* encrypt_r: (libc)DES Encryption.
* endfsent: (libc)fstab.
* endgrent: (libc)Scanning All Groups.
* endhostent: (libc)Host Names.
* endmntent: (libc)mtab.
* endnetent: (libc)Networks Database.
* endnetgrent: (libc)Lookup Netgroup.
* endprotoent: (libc)Protocols Database.
* endpwent: (libc)Scanning All Users.
* endservent: (libc)Services Database.
* endutent: (libc)Manipulating the Database.
* endutxent: (libc)XPG Functions.
* ENEEDAUTH: (libc)Error Codes.
* ENETDOWN: (libc)Error Codes.
* ENETRESET: (libc)Error Codes.
* ENETUNREACH: (libc)Error Codes.
* ENFILE: (libc)Error Codes.
* ENOANO: (libc)Error Codes.
* ENOBUFS: (libc)Error Codes.
* ENOCSI: (libc)Error Codes.
* ENODATA: (libc)Error Codes.
* ENODEV: (libc)Error Codes.
* ENOENT: (libc)Error Codes.
* ENOEXEC: (libc)Error Codes.
* ENOKEY: (libc)Error Codes.
* ENOLCK: (libc)Error Codes.
* ENOLINK: (libc)Error Codes.
* ENOMEDIUM: (libc)Error Codes.
* ENOMEM: (libc)Error Codes.
* ENOMSG: (libc)Error Codes.
* ENONET: (libc)Error Codes.
* ENOPKG: (libc)Error Codes.
* ENOPROTOOPT: (libc)Error Codes.
* ENOSPC: (libc)Error Codes.
* ENOSR: (libc)Error Codes.
* ENOSTR: (libc)Error Codes.
* ENOSYS: (libc)Error Codes.
* ENOTBLK: (libc)Error Codes.
* ENOTCONN: (libc)Error Codes.
* ENOTDIR: (libc)Error Codes.
* ENOTEMPTY: (libc)Error Codes.
* ENOTNAM: (libc)Error Codes.
* ENOTRECOVERABLE: (libc)Error Codes.
* ENOTSOCK: (libc)Error Codes.
* ENOTSUP: (libc)Error Codes.
* ENOTTY: (libc)Error Codes.
* ENOTUNIQ: (libc)Error Codes.
* envz_add: (libc)Envz Functions.
* envz_entry: (libc)Envz Functions.
* envz_get: (libc)Envz Functions.
* envz_merge: (libc)Envz Functions.
* envz_remove: (libc)Envz Functions.
* envz_strip: (libc)Envz Functions.
* ENXIO: (libc)Error Codes.
* EOF: (libc)EOF and Errors.
* EOPNOTSUPP: (libc)Error Codes.
* EOVERFLOW: (libc)Error Codes.
* EOWNERDEAD: (libc)Error Codes.
* EPERM: (libc)Error Codes.
* EPFNOSUPPORT: (libc)Error Codes.
* EPIPE: (libc)Error Codes.
* EPROCLIM: (libc)Error Codes.
* EPROCUNAVAIL: (libc)Error Codes.
* EPROGMISMATCH: (libc)Error Codes.
* EPROGUNAVAIL: (libc)Error Codes.
* EPROTO: (libc)Error Codes.
* EPROTONOSUPPORT: (libc)Error Codes.
* EPROTOTYPE: (libc)Error Codes.
* EQUIV_CLASS_MAX: (libc)Utility Limits.
* erand48: (libc)SVID Random.
* erand48_r: (libc)SVID Random.
* ERANGE: (libc)Error Codes.
* EREMCHG: (libc)Error Codes.
* EREMOTEIO: (libc)Error Codes.
* EREMOTE: (libc)Error Codes.
* ERESTART: (libc)Error Codes.
* erfcf: (libc)Special Functions.
* erfc: (libc)Special Functions.
* erfcl: (libc)Special Functions.
* erff: (libc)Special Functions.
* ERFKILL: (libc)Error Codes.
* erf: (libc)Special Functions.
* erfl: (libc)Special Functions.
* EROFS: (libc)Error Codes.
* ERPCMISMATCH: (libc)Error Codes.
* err: (libc)Error Messages.
* errno: (libc)Checking for Errors.
* error_at_line: (libc)Error Messages.
* error: (libc)Error Messages.
* errx: (libc)Error Messages.
* ESHUTDOWN: (libc)Error Codes.
* ESOCKTNOSUPPORT: (libc)Error Codes.
* ESPIPE: (libc)Error Codes.
* ESRCH: (libc)Error Codes.
* ESRMNT: (libc)Error Codes.
* ESTALE: (libc)Error Codes.
* ESTRPIPE: (libc)Error Codes.
* ETIMEDOUT: (libc)Error Codes.
* ETIME: (libc)Error Codes.
* ETOOMANYREFS: (libc)Error Codes.
* ETXTBSY: (libc)Error Codes.
* EUCLEAN: (libc)Error Codes.
* EUNATCH: (libc)Error Codes.
* EUSERS: (libc)Error Codes.
* EWOULDBLOCK: (libc)Error Codes.
* EXDEV: (libc)Error Codes.
* execle: (libc)Executing a File.
* execl: (libc)Executing a File.
* execlp: (libc)Executing a File.
* execve: (libc)Executing a File.
* execv: (libc)Executing a File.
* execvp: (libc)Executing a File.
* EXFULL: (libc)Error Codes.
* EXIT_FAILURE: (libc)Exit Status.
* exit: (libc)Normal Termination.
* _exit: (libc)Termination Internals.
* _Exit: (libc)Termination Internals.
* EXIT_SUCCESS: (libc)Exit Status.
* exp10f: (libc)Exponents and Logarithms.
* exp10: (libc)Exponents and Logarithms.
* exp10l: (libc)Exponents and Logarithms.
* exp2f: (libc)Exponents and Logarithms.
* exp2: (libc)Exponents and Logarithms.
* exp2l: (libc)Exponents and Logarithms.
* expf: (libc)Exponents and Logarithms.
* exp: (libc)Exponents and Logarithms.
* explicit_bzero: (libc)Erasing Sensitive Data.
* expl: (libc)Exponents and Logarithms.
* expm1f: (libc)Exponents and Logarithms.
* expm1: (libc)Exponents and Logarithms.
* expm1l: (libc)Exponents and Logarithms.
* EXPR_NEST_MAX: (libc)Utility Limits.
* fabsf: (libc)Absolute Value.
* fabs: (libc)Absolute Value.
* fabsl: (libc)Absolute Value.
* __fbufsize: (libc)Controlling Buffering.
* fchdir: (libc)Working Directory.
* fchmod: (libc)Setting Permissions.
* fchown: (libc)File Owner.
* fcloseall: (libc)Closing Streams.
* fclose: (libc)Closing Streams.
* fcntl: (libc)Control Operations.
* fcvt: (libc)System V Number Conversion.
* fcvt_r: (libc)System V Number Conversion.
* fdatasync: (libc)Synchronizing I/O.
* FD_CLOEXEC: (libc)Descriptor Flags.
* FD_CLR: (libc)Waiting for I/O.
* fdimf: (libc)Misc FP Arithmetic.
* fdim: (libc)Misc FP Arithmetic.
* fdiml: (libc)Misc FP Arithmetic.
* FD_ISSET: (libc)Waiting for I/O.
* fdopendir: (libc)Opening a Directory.
* fdopen: (libc)Descriptors and Streams.
* FD_SET: (libc)Waiting for I/O.
* FD_SETSIZE: (libc)Waiting for I/O.
* F_DUPFD: (libc)Duplicating Descriptors.
* FD_ZERO: (libc)Waiting for I/O.
* feclearexcept: (libc)Status bit operations.
* fedisableexcept: (libc)Control Functions.
* feenableexcept: (libc)Control Functions.
* fegetenv: (libc)Control Functions.
* fegetexceptflag: (libc)Status bit operations.
* fegetexcept: (libc)Control Functions.
* fegetmode: (libc)Control Functions.
* fegetround: (libc)Rounding.
* feholdexcept: (libc)Control Functions.
* feof: (libc)EOF and Errors.
* feof_unlocked: (libc)EOF and Errors.
* feraiseexcept: (libc)Status bit operations.
* ferror: (libc)EOF and Errors.
* ferror_unlocked: (libc)EOF and Errors.
* fesetenv: (libc)Control Functions.
* fesetexceptflag: (libc)Status bit operations.
* fesetexcept: (libc)Status bit operations.
* fesetmode: (libc)Control Functions.
* fesetround: (libc)Rounding.
* FE_SNANS_ALWAYS_SIGNAL: (libc)Infinity and NaN.
* fetestexceptflag: (libc)Status bit operations.
* fetestexcept: (libc)Status bit operations.
* feupdateenv: (libc)Control Functions.
* fflush: (libc)Flushing Buffers.
* fflush_unlocked: (libc)Flushing Buffers.
* fgetc: (libc)Character Input.
* fgetc_unlocked: (libc)Character Input.
* F_GETFD: (libc)Descriptor Flags.
* F_GETFL: (libc)Getting File Status Flags.
* fgetgrent: (libc)Scanning All Groups.
* fgetgrent_r: (libc)Scanning All Groups.
* F_GETLK: (libc)File Locks.
* F_GETOWN: (libc)Interrupt Input.
* fgetpos64: (libc)Portable Positioning.
* fgetpos: (libc)Portable Positioning.
* fgetpwent: (libc)Scanning All Users.
* fgetpwent_r: (libc)Scanning All Users.
* fgets: (libc)Line Input.
* fgets_unlocked: (libc)Line Input.
* fgetwc: (libc)Character Input.
* fgetwc_unlocked: (libc)Character Input.
* fgetws: (libc)Line Input.
* fgetws_unlocked: (libc)Line Input.
* FILENAME_MAX: (libc)Limits for Files.
* fileno: (libc)Descriptors and Streams.
* fileno_unlocked: (libc)Descriptors and Streams.
* finitef: (libc)Floating Point Classes.
* finite: (libc)Floating Point Classes.
* finitel: (libc)Floating Point Classes.
* __flbf: (libc)Controlling Buffering.
* flockfile: (libc)Streams and Threads.
* floorf: (libc)Rounding Functions.
* floor: (libc)Rounding Functions.
* floorl: (libc)Rounding Functions.
* _flushlbf: (libc)Flushing Buffers.
* FLUSHO: (libc)Local Modes.
* fmaf: (libc)Misc FP Arithmetic.
* fma: (libc)Misc FP Arithmetic.
* fmal: (libc)Misc FP Arithmetic.
* fmaxf: (libc)Misc FP Arithmetic.
* fmax: (libc)Misc FP Arithmetic.
* fmaxl: (libc)Misc FP Arithmetic.
* fmaxmagf: (libc)Misc FP Arithmetic.
* fmaxmag: (libc)Misc FP Arithmetic.
* fmaxmagl: (libc)Misc FP Arithmetic.
* fmemopen: (libc)String Streams.
* fminf: (libc)Misc FP Arithmetic.
* fmin: (libc)Misc FP Arithmetic.
* fminl: (libc)Misc FP Arithmetic.
* fminmagf: (libc)Misc FP Arithmetic.
* fminmag: (libc)Misc FP Arithmetic.
* fminmagl: (libc)Misc FP Arithmetic.
* fmodf: (libc)Remainder Functions.
* fmod: (libc)Remainder Functions.
* fmodl: (libc)Remainder Functions.
* fmtmsg: (libc)Printing Formatted Messages.
* fnmatch: (libc)Wildcard Matching.
* F_OFD_GETLK: (libc)Open File Description Locks.
* F_OFD_SETLK: (libc)Open File Description Locks.
* F_OFD_SETLKW: (libc)Open File Description Locks.
* F_OK: (libc)Testing File Access.
* fopen64: (libc)Opening Streams.
* fopencookie: (libc)Streams and Cookies.
* fopen: (libc)Opening Streams.
* FOPEN_MAX: (libc)Opening Streams.
* fork: (libc)Creating a Process.
* forkpty: (libc)Pseudo-Terminal Pairs.
* fpathconf: (libc)Pathconf.
* fpclassify: (libc)Floating Point Classes.
* __fpending: (libc)Controlling Buffering.
* FP_ILOGB0: (libc)Exponents and Logarithms.
* FP_ILOGBNAN: (libc)Exponents and Logarithms.
* FP_LLOGB0: (libc)Exponents and Logarithms.
* FP_LLOGBNAN: (libc)Exponents and Logarithms.
* fprintf: (libc)Formatted Output Functions.
* __fpurge: (libc)Flushing Buffers.
* fputc: (libc)Simple Output.
* fputc_unlocked: (libc)Simple Output.
* fputs: (libc)Simple Output.
* fputs_unlocked: (libc)Simple Output.
* fputwc: (libc)Simple Output.
* fputwc_unlocked: (libc)Simple Output.
* fputws: (libc)Simple Output.
* fputws_unlocked: (libc)Simple Output.
* __freadable: (libc)Opening Streams.
* __freading: (libc)Opening Streams.
* fread: (libc)Block Input/Output.
* fread_unlocked: (libc)Block Input/Output.
* free: (libc)Freeing after Malloc.
* freopen64: (libc)Opening Streams.
* freopen: (libc)Opening Streams.
* frexpf: (libc)Normalization Functions.
* frexp: (libc)Normalization Functions.
* frexpl: (libc)Normalization Functions.
* fromfpf: (libc)Rounding Functions.
* fromfp: (libc)Rounding Functions.
* fromfpl: (libc)Rounding Functions.
* fromfpxf: (libc)Rounding Functions.
* fromfpx: (libc)Rounding Functions.
* fromfpxl: (libc)Rounding Functions.
* fscanf: (libc)Formatted Input Functions.
* fseek: (libc)File Positioning.
* fseeko64: (libc)File Positioning.
* fseeko: (libc)File Positioning.
* F_SETFD: (libc)Descriptor Flags.
* F_SETFL: (libc)Getting File Status Flags.
* F_SETLK: (libc)File Locks.
* F_SETLKW: (libc)File Locks.
* __fsetlocking: (libc)Streams and Threads.
* F_SETOWN: (libc)Interrupt Input.
* fsetpos64: (libc)Portable Positioning.
* fsetpos: (libc)Portable Positioning.
* fstat64: (libc)Reading Attributes.
* fstat: (libc)Reading Attributes.
* fsync: (libc)Synchronizing I/O.
* ftell: (libc)File Positioning.
* ftello64: (libc)File Positioning.
* ftello: (libc)File Positioning.
* ftruncate64: (libc)File Size.
* ftruncate: (libc)File Size.
* ftrylockfile: (libc)Streams and Threads.
* ftw64: (libc)Working with Directory Trees.
* ftw: (libc)Working with Directory Trees.
* funlockfile: (libc)Streams and Threads.
* futimes: (libc)File Times.
* fwide: (libc)Streams and I18N.
* fwprintf: (libc)Formatted Output Functions.
* __fwritable: (libc)Opening Streams.
* fwrite: (libc)Block Input/Output.
* fwrite_unlocked: (libc)Block Input/Output.
* __fwriting: (libc)Opening Streams.
* fwscanf: (libc)Formatted Input Functions.
* gammaf: (libc)Special Functions.
* gamma: (libc)Special Functions.
* gammal: (libc)Special Functions.
* __gconv_end_fct: (libc)glibc iconv Implementation.
* __gconv_fct: (libc)glibc iconv Implementation.
* __gconv_init_fct: (libc)glibc iconv Implementation.
* gcvt: (libc)System V Number Conversion.
* getauxval: (libc)Auxiliary Vector.
* get_avphys_pages: (libc)Query Memory Parameters.
* getchar: (libc)Character Input.
* getchar_unlocked: (libc)Character Input.
* getc: (libc)Character Input.
* getcontext: (libc)System V contexts.
* getc_unlocked: (libc)Character Input.
* get_current_dir_name: (libc)Working Directory.
* getcwd: (libc)Working Directory.
* getdate: (libc)General Time String Parsing.
* getdate_r: (libc)General Time String Parsing.
* getdelim: (libc)Line Input.
* getdomainnname: (libc)Host Identification.
* getegid: (libc)Reading Persona.
* getentropy: (libc)Unpredictable Bytes.
* getenv: (libc)Environment Access.
* geteuid: (libc)Reading Persona.
* getfsent: (libc)fstab.
* getfsfile: (libc)fstab.
* getfsspec: (libc)fstab.
* getgid: (libc)Reading Persona.
* getgrent: (libc)Scanning All Groups.
* getgrent_r: (libc)Scanning All Groups.
* getgrgid: (libc)Lookup Group.
* getgrgid_r: (libc)Lookup Group.
* getgrnam: (libc)Lookup Group.
* getgrnam_r: (libc)Lookup Group.
* getgrouplist: (libc)Setting Groups.
* getgroups: (libc)Reading Persona.
* gethostbyaddr: (libc)Host Names.
* gethostbyaddr_r: (libc)Host Names.
* gethostbyname2: (libc)Host Names.
* gethostbyname2_r: (libc)Host Names.
* gethostbyname: (libc)Host Names.
* gethostbyname_r: (libc)Host Names.
* gethostent: (libc)Host Names.
* gethostid: (libc)Host Identification.
* gethostname: (libc)Host Identification.
* getitimer: (libc)Setting an Alarm.
* getline: (libc)Line Input.
* getloadavg: (libc)Processor Resources.
* getlogin: (libc)Who Logged In.
* getmntent: (libc)mtab.
* getmntent_r: (libc)mtab.
* getnetbyaddr: (libc)Networks Database.
* getnetbyname: (libc)Networks Database.
* getnetent: (libc)Networks Database.
* getnetgrent: (libc)Lookup Netgroup.
* getnetgrent_r: (libc)Lookup Netgroup.
* get_nprocs_conf: (libc)Processor Resources.
* get_nprocs: (libc)Processor Resources.
* getopt: (libc)Using Getopt.
* getopt_long: (libc)Getopt Long Options.
* getopt_long_only: (libc)Getopt Long Options.
* getpagesize: (libc)Query Memory Parameters.
* getpass: (libc)getpass.
* getpayloadf: (libc)FP Bit Twiddling.
* getpayload: (libc)FP Bit Twiddling.
* getpayloadl: (libc)FP Bit Twiddling.
* getpeername: (libc)Who is Connected.
* getpgid: (libc)Process Group Functions.
* getpgrp: (libc)Process Group Functions.
* get_phys_pages: (libc)Query Memory Parameters.
* getpid: (libc)Process Identification.
* getppid: (libc)Process Identification.
* getpriority: (libc)Traditional Scheduling Functions.
* getprotobyname: (libc)Protocols Database.
* getprotobynumber: (libc)Protocols Database.
* getprotoent: (libc)Protocols Database.
* getpt: (libc)Allocation.
* getpwent: (libc)Scanning All Users.
* getpwent_r: (libc)Scanning All Users.
* getpwnam: (libc)Lookup User.
* getpwnam_r: (libc)Lookup User.
* getpwuid: (libc)Lookup User.
* getpwuid_r: (libc)Lookup User.
* getrandom: (libc)Unpredictable Bytes.
* getrlimit64: (libc)Limits on Resources.
* getrlimit: (libc)Limits on Resources.
* getrusage: (libc)Resource Usage.
* getservbyname: (libc)Services Database.
* getservbyport: (libc)Services Database.
* getservent: (libc)Services Database.
* getsid: (libc)Process Group Functions.
* gets: (libc)Line Input.
* getsockname: (libc)Reading Address.
* getsockopt: (libc)Socket Option Functions.
* getsubopt: (libc)Suboptions.
* gettext: (libc)Translation with gettext.
* gettimeofday: (libc)High-Resolution Calendar.
* getuid: (libc)Reading Persona.
* getumask: (libc)Setting Permissions.
* getutent: (libc)Manipulating the Database.
* getutent_r: (libc)Manipulating the Database.
* getutid: (libc)Manipulating the Database.
* getutid_r: (libc)Manipulating the Database.
* getutline: (libc)Manipulating the Database.
* getutline_r: (libc)Manipulating the Database.
* getutmp: (libc)XPG Functions.
* getutmpx: (libc)XPG Functions.
* getutxent: (libc)XPG Functions.
* getutxid: (libc)XPG Functions.
* getutxline: (libc)XPG Functions.
* getwchar: (libc)Character Input.
* getwchar_unlocked: (libc)Character Input.
* getwc: (libc)Character Input.
* getwc_unlocked: (libc)Character Input.
* getwd: (libc)Working Directory.
* getw: (libc)Character Input.
* glob64: (libc)Calling Glob.
* globfree64: (libc)More Flags for Globbing.
* globfree: (libc)More Flags for Globbing.
* glob: (libc)Calling Glob.
* gmtime: (libc)Broken-down Time.
* gmtime_r: (libc)Broken-down Time.
* grantpt: (libc)Allocation.
* gsignal: (libc)Signaling Yourself.
* gtty: (libc)BSD Terminal Modes.
* hasmntopt: (libc)mtab.
* hcreate: (libc)Hash Search Function.
* hcreate_r: (libc)Hash Search Function.
* hdestroy: (libc)Hash Search Function.
* hdestroy_r: (libc)Hash Search Function.
* hsearch: (libc)Hash Search Function.
* hsearch_r: (libc)Hash Search Function.
* htonl: (libc)Byte Order.
* htons: (libc)Byte Order.
* HUGE_VALF: (libc)Math Error Reporting.
* HUGE_VAL: (libc)Math Error Reporting.
* HUGE_VALL: (libc)Math Error Reporting.
* HUPCL: (libc)Control Modes.
* hypotf: (libc)Exponents and Logarithms.
* hypot: (libc)Exponents and Logarithms.
* hypotl: (libc)Exponents and Logarithms.
* ICANON: (libc)Local Modes.
* iconv_close: (libc)Generic Conversion Interface.
* iconv: (libc)Generic Conversion Interface.
* iconv_open: (libc)Generic Conversion Interface.
* ICRNL: (libc)Input Modes.
* IEXTEN: (libc)Local Modes.
* if_freenameindex: (libc)Interface Naming.
* if_indextoname: (libc)Interface Naming.
* if_nameindex: (libc)Interface Naming.
* if_nametoindex: (libc)Interface Naming.
* IFNAMSIZ: (libc)Interface Naming.
* IFTODT: (libc)Directory Entries.
* IGNBRK: (libc)Input Modes.
* IGNCR: (libc)Input Modes.
* IGNPAR: (libc)Input Modes.
* I: (libc)Complex Numbers.
* ilogbf: (libc)Exponents and Logarithms.
* ilogb: (libc)Exponents and Logarithms.
* ilogbl: (libc)Exponents and Logarithms.
* _Imaginary_I: (libc)Complex Numbers.
* imaxabs: (libc)Absolute Value.
* IMAXBEL: (libc)Input Modes.
* imaxdiv: (libc)Integer Division.
* in6addr_any: (libc)Host Address Data Type.
* in6addr_loopback: (libc)Host Address Data Type.
* INADDR_ANY: (libc)Host Address Data Type.
* INADDR_BROADCAST: (libc)Host Address Data Type.
* INADDR_LOOPBACK: (libc)Host Address Data Type.
* INADDR_NONE: (libc)Host Address Data Type.
* index: (libc)Search Functions.
* inet_addr: (libc)Host Address Functions.
* inet_aton: (libc)Host Address Functions.
* inet_lnaof: (libc)Host Address Functions.
* inet_makeaddr: (libc)Host Address Functions.
* inet_netof: (libc)Host Address Functions.
* inet_network: (libc)Host Address Functions.
* inet_ntoa: (libc)Host Address Functions.
* inet_ntop: (libc)Host Address Functions.
* inet_pton: (libc)Host Address Functions.
* INFINITY: (libc)Infinity and NaN.
* initgroups: (libc)Setting Groups.
* initstate: (libc)BSD Random.
* initstate_r: (libc)BSD Random.
* INLCR: (libc)Input Modes.
* innetgr: (libc)Netgroup Membership.
* INPCK: (libc)Input Modes.
* ioctl: (libc)IOCTLs.
* _IOFBF: (libc)Controlling Buffering.
* _IOLBF: (libc)Controlling Buffering.
* _IONBF: (libc)Controlling Buffering.
* IPPORT_RESERVED: (libc)Ports.
* IPPORT_USERRESERVED: (libc)Ports.
* isalnum: (libc)Classification of Characters.
* isalpha: (libc)Classification of Characters.
* isascii: (libc)Classification of Characters.
* isatty: (libc)Is It a Terminal.
* isblank: (libc)Classification of Characters.
* iscanonical: (libc)Floating Point Classes.
* iscntrl: (libc)Classification of Characters.
* isdigit: (libc)Classification of Characters.
* iseqsig: (libc)FP Comparison Functions.
* isfinite: (libc)Floating Point Classes.
* isgraph: (libc)Classification of Characters.
* isgreaterequal: (libc)FP Comparison Functions.
* isgreater: (libc)FP Comparison Functions.
* ISIG: (libc)Local Modes.
* isinff: (libc)Floating Point Classes.
* isinf: (libc)Floating Point Classes.
* isinfl: (libc)Floating Point Classes.
* islessequal: (libc)FP Comparison Functions.
* islessgreater: (libc)FP Comparison Functions.
* isless: (libc)FP Comparison Functions.
* islower: (libc)Classification of Characters.
* isnanf: (libc)Floating Point Classes.
* isnan: (libc)Floating Point Classes.
* isnan: (libc)Floating Point Classes.
* isnanl: (libc)Floating Point Classes.
* isnormal: (libc)Floating Point Classes.
* isprint: (libc)Classification of Characters.
* ispunct: (libc)Classification of Characters.
* issignaling: (libc)Floating Point Classes.
* isspace: (libc)Classification of Characters.
* issubnormal: (libc)Floating Point Classes.
* ISTRIP: (libc)Input Modes.
* isunordered: (libc)FP Comparison Functions.
* isupper: (libc)Classification of Characters.
* iswalnum: (libc)Classification of Wide Characters.
* iswalpha: (libc)Classification of Wide Characters.
* iswblank: (libc)Classification of Wide Characters.
* iswcntrl: (libc)Classification of Wide Characters.
* iswctype: (libc)Classification of Wide Characters.
* iswdigit: (libc)Classification of Wide Characters.
* iswgraph: (libc)Classification of Wide Characters.
* iswlower: (libc)Classification of Wide Characters.
* iswprint: (libc)Classification of Wide Characters.
* iswpunct: (libc)Classification of Wide Characters.
* iswspace: (libc)Classification of Wide Characters.
* iswupper: (libc)Classification of Wide Characters.
* iswxdigit: (libc)Classification of Wide Characters.
* isxdigit: (libc)Classification of Characters.
* iszero: (libc)Floating Point Classes.
* IXANY: (libc)Input Modes.
* IXOFF: (libc)Input Modes.
* IXON: (libc)Input Modes.
* j0f: (libc)Special Functions.
* j0: (libc)Special Functions.
* j0l: (libc)Special Functions.
* j1f: (libc)Special Functions.
* j1: (libc)Special Functions.
* j1l: (libc)Special Functions.
* jnf: (libc)Special Functions.
* jn: (libc)Special Functions.
* jnl: (libc)Special Functions.
* jrand48: (libc)SVID Random.
* jrand48_r: (libc)SVID Random.
* kill: (libc)Signaling Another Process.
* killpg: (libc)Signaling Another Process.
* l64a: (libc)Encode Binary Data.
* labs: (libc)Absolute Value.
* lcong48: (libc)SVID Random.
* lcong48_r: (libc)SVID Random.
* L_ctermid: (libc)Identifying the Terminal.
* L_cuserid: (libc)Who Logged In.
* ldexpf: (libc)Normalization Functions.
* ldexp: (libc)Normalization Functions.
* ldexpl: (libc)Normalization Functions.
* ldiv: (libc)Integer Division.
* lfind: (libc)Array Search Function.
* lgammaf: (libc)Special Functions.
* lgammaf_r: (libc)Special Functions.
* lgamma: (libc)Special Functions.
* lgammal: (libc)Special Functions.
* lgammal_r: (libc)Special Functions.
* lgamma_r: (libc)Special Functions.
* LINE_MAX: (libc)Utility Limits.
* link: (libc)Hard Links.
* LINK_MAX: (libc)Limits for Files.
* lio_listio64: (libc)Asynchronous Reads/Writes.
* lio_listio: (libc)Asynchronous Reads/Writes.
* listen: (libc)Listening.
* llabs: (libc)Absolute Value.
* lldiv: (libc)Integer Division.
* llogbf: (libc)Exponents and Logarithms.
* llogb: (libc)Exponents and Logarithms.
* llogbl: (libc)Exponents and Logarithms.
* llrintf: (libc)Rounding Functions.
* llrint: (libc)Rounding Functions.
* llrintl: (libc)Rounding Functions.
* llroundf: (libc)Rounding Functions.
* llround: (libc)Rounding Functions.
* llroundl: (libc)Rounding Functions.
* localeconv: (libc)The Lame Way to Locale Data.
* localtime: (libc)Broken-down Time.
* localtime_r: (libc)Broken-down Time.
* log10f: (libc)Exponents and Logarithms.
* log10: (libc)Exponents and Logarithms.
* log10l: (libc)Exponents and Logarithms.
* log1pf: (libc)Exponents and Logarithms.
* log1p: (libc)Exponents and Logarithms.
* log1pl: (libc)Exponents and Logarithms.
* log2f: (libc)Exponents and Logarithms.
* log2: (libc)Exponents and Logarithms.
* log2l: (libc)Exponents and Logarithms.
* logbf: (libc)Exponents and Logarithms.
* logb: (libc)Exponents and Logarithms.
* logbl: (libc)Exponents and Logarithms.
* logf: (libc)Exponents and Logarithms.
* login: (libc)Logging In and Out.
* login_tty: (libc)Logging In and Out.
* log: (libc)Exponents and Logarithms.
* logl: (libc)Exponents and Logarithms.
* logout: (libc)Logging In and Out.
* logwtmp: (libc)Logging In and Out.
* longjmp: (libc)Non-Local Details.
* lrand48: (libc)SVID Random.
* lrand48_r: (libc)SVID Random.
* lrintf: (libc)Rounding Functions.
* lrint: (libc)Rounding Functions.
* lrintl: (libc)Rounding Functions.
* lroundf: (libc)Rounding Functions.
* lround: (libc)Rounding Functions.
* lroundl: (libc)Rounding Functions.
* lsearch: (libc)Array Search Function.
* lseek64: (libc)File Position Primitive.
* lseek: (libc)File Position Primitive.
* lstat64: (libc)Reading Attributes.
* lstat: (libc)Reading Attributes.
* L_tmpnam: (libc)Temporary Files.
* lutimes: (libc)File Times.
* madvise: (libc)Memory-mapped I/O.
* makecontext: (libc)System V contexts.
* mallinfo: (libc)Statistics of Malloc.
* malloc: (libc)Basic Allocation.
* mallopt: (libc)Malloc Tunable Parameters.
* MAX_CANON: (libc)Limits for Files.
* MAX_INPUT: (libc)Limits for Files.
* MAXNAMLEN: (libc)Limits for Files.
* MAXSYMLINKS: (libc)Symbolic Links.
* MB_CUR_MAX: (libc)Selecting the Conversion.
* mblen: (libc)Non-reentrant Character Conversion.
* MB_LEN_MAX: (libc)Selecting the Conversion.
* mbrlen: (libc)Converting a Character.
* mbrtowc: (libc)Converting a Character.
* mbsinit: (libc)Keeping the state.
* mbsnrtowcs: (libc)Converting Strings.
* mbsrtowcs: (libc)Converting Strings.
* mbstowcs: (libc)Non-reentrant String Conversion.
* mbtowc: (libc)Non-reentrant Character Conversion.
* mcheck: (libc)Heap Consistency Checking.
* MDMBUF: (libc)Control Modes.
* memalign: (libc)Aligned Memory Blocks.
* memccpy: (libc)Copying Strings and Arrays.
* memchr: (libc)Search Functions.
* memcmp: (libc)String/Array Comparison.
* memcpy: (libc)Copying Strings and Arrays.
* memfrob: (libc)Trivial Encryption.
* memmem: (libc)Search Functions.
* memmove: (libc)Copying Strings and Arrays.
* mempcpy: (libc)Copying Strings and Arrays.
* memrchr: (libc)Search Functions.
* memset: (libc)Copying Strings and Arrays.
* mkdir: (libc)Creating Directories.
* mkdtemp: (libc)Temporary Files.
* mkfifo: (libc)FIFO Special Files.
* mknod: (libc)Making Special Files.
* mkstemp: (libc)Temporary Files.
* mktemp: (libc)Temporary Files.
* mktime: (libc)Broken-down Time.
* mlockall: (libc)Page Lock Functions.
* mlock: (libc)Page Lock Functions.
* mmap64: (libc)Memory-mapped I/O.
* mmap: (libc)Memory-mapped I/O.
* modff: (libc)Rounding Functions.
* modf: (libc)Rounding Functions.
* modfl: (libc)Rounding Functions.
* mount: (libc)Mount-Unmount-Remount.
* mprobe: (libc)Heap Consistency Checking.
* mrand48: (libc)SVID Random.
* mrand48_r: (libc)SVID Random.
* mremap: (libc)Memory-mapped I/O.
* MSG_DONTROUTE: (libc)Socket Data Options.
* MSG_OOB: (libc)Socket Data Options.
* MSG_PEEK: (libc)Socket Data Options.
* msync: (libc)Memory-mapped I/O.
* mtrace: (libc)Tracing malloc.
* munlockall: (libc)Page Lock Functions.
* munlock: (libc)Page Lock Functions.
* munmap: (libc)Memory-mapped I/O.
* muntrace: (libc)Tracing malloc.
* NAME_MAX: (libc)Limits for Files.
* nanf: (libc)FP Bit Twiddling.
* nan: (libc)FP Bit Twiddling.
* NAN: (libc)Infinity and NaN.
* nanl: (libc)FP Bit Twiddling.
* nanosleep: (libc)Sleeping.
* NCCS: (libc)Mode Data Types.
* nearbyintf: (libc)Rounding Functions.
* nearbyint: (libc)Rounding Functions.
* nearbyintl: (libc)Rounding Functions.
* nextafterf: (libc)FP Bit Twiddling.
* nextafter: (libc)FP Bit Twiddling.
* nextafterl: (libc)FP Bit Twiddling.
* nextdownf: (libc)FP Bit Twiddling.
* nextdown: (libc)FP Bit Twiddling.
* nextdownl: (libc)FP Bit Twiddling.
* nexttowardf: (libc)FP Bit Twiddling.
* nexttoward: (libc)FP Bit Twiddling.
* nexttowardl: (libc)FP Bit Twiddling.
* nextupf: (libc)FP Bit Twiddling.
* nextup: (libc)FP Bit Twiddling.
* nextupl: (libc)FP Bit Twiddling.
* nftw64: (libc)Working with Directory Trees.
* nftw: (libc)Working with Directory Trees.
* ngettext: (libc)Advanced gettext functions.
* NGROUPS_MAX: (libc)General Limits.
* nice: (libc)Traditional Scheduling Functions.
* nl_langinfo: (libc)The Elegant and Fast Way.
* NOFLSH: (libc)Local Modes.
* NOKERNINFO: (libc)Local Modes.
* nrand48: (libc)SVID Random.
* nrand48_r: (libc)SVID Random.
* NSIG: (libc)Standard Signals.
* ntohl: (libc)Byte Order.
* ntohs: (libc)Byte Order.
* ntp_adjtime: (libc)High Accuracy Clock.
* ntp_gettime: (libc)High Accuracy Clock.
* NULL: (libc)Null Pointer Constant.
* O_ACCMODE: (libc)Access Modes.
* O_APPEND: (libc)Operating Modes.
* O_ASYNC: (libc)Operating Modes.
* obstack_1grow_fast: (libc)Extra Fast Growing.
* obstack_1grow: (libc)Growing Objects.
* obstack_alignment_mask: (libc)Obstacks Data Alignment.
* obstack_alloc: (libc)Allocation in an Obstack.
* obstack_base: (libc)Status of an Obstack.
* obstack_blank_fast: (libc)Extra Fast Growing.
* obstack_blank: (libc)Growing Objects.
* obstack_chunk_size: (libc)Obstack Chunks.
* obstack_copy0: (libc)Allocation in an Obstack.
* obstack_copy: (libc)Allocation in an Obstack.
* obstack_finish: (libc)Growing Objects.
* obstack_free: (libc)Freeing Obstack Objects.
* obstack_grow0: (libc)Growing Objects.
* obstack_grow: (libc)Growing Objects.
* obstack_init: (libc)Preparing for Obstacks.
* obstack_int_grow_fast: (libc)Extra Fast Growing.
* obstack_int_grow: (libc)Growing Objects.
* obstack_next_free: (libc)Status of an Obstack.
* obstack_object_size: (libc)Growing Objects.
* obstack_object_size: (libc)Status of an Obstack.
* obstack_printf: (libc)Dynamic Output.
* obstack_ptr_grow_fast: (libc)Extra Fast Growing.
* obstack_ptr_grow: (libc)Growing Objects.
* obstack_room: (libc)Extra Fast Growing.
* obstack_vprintf: (libc)Variable Arguments Output.
* O_CREAT: (libc)Open-time Flags.
* O_EXCL: (libc)Open-time Flags.
* O_EXEC: (libc)Access Modes.
* O_EXLOCK: (libc)Open-time Flags.
* offsetof: (libc)Structure Measurement.
* O_FSYNC: (libc)Operating Modes.
* O_IGNORE_CTTY: (libc)Open-time Flags.
* O_NDELAY: (libc)Operating Modes.
* on_exit: (libc)Cleanups on Exit.
* ONLCR: (libc)Output Modes.
* O_NOATIME: (libc)Operating Modes.
* O_NOCTTY: (libc)Open-time Flags.
* ONOEOT: (libc)Output Modes.
* O_NOLINK: (libc)Open-time Flags.
* O_NONBLOCK: (libc)Open-time Flags.
* O_NONBLOCK: (libc)Operating Modes.
* O_NOTRANS: (libc)Open-time Flags.
* open64: (libc)Opening and Closing Files.
* opendir: (libc)Opening a Directory.
* open: (libc)Opening and Closing Files.
* openlog: (libc)openlog.
* OPEN_MAX: (libc)General Limits.
* open_memstream: (libc)String Streams.
* openpty: (libc)Pseudo-Terminal Pairs.
* OPOST: (libc)Output Modes.
* O_RDONLY: (libc)Access Modes.
* O_RDWR: (libc)Access Modes.
* O_READ: (libc)Access Modes.
* O_SHLOCK: (libc)Open-time Flags.
* O_SYNC: (libc)Operating Modes.
* O_TRUNC: (libc)Open-time Flags.
* O_WRITE: (libc)Access Modes.
* O_WRONLY: (libc)Access Modes.
* OXTABS: (libc)Output Modes.
* PA_FLAG_MASK: (libc)Parsing a Template String.
* PARENB: (libc)Control Modes.
* PARMRK: (libc)Input Modes.
* PARODD: (libc)Control Modes.
* parse_printf_format: (libc)Parsing a Template String.
* pathconf: (libc)Pathconf.
* PATH_MAX: (libc)Limits for Files.
* _PATH_UTMP: (libc)Manipulating the Database.
* _PATH_WTMP: (libc)Manipulating the Database.
* pause: (libc)Using Pause.
* pclose: (libc)Pipe to a Subprocess.
* PENDIN: (libc)Local Modes.
* perror: (libc)Error Messages.
* PF_FILE: (libc)Local Namespace Details.
* PF_INET6: (libc)Internet Namespace.
* PF_INET: (libc)Internet Namespace.
* PF_LOCAL: (libc)Local Namespace Details.
* PF_UNIX: (libc)Local Namespace Details.
* PIPE_BUF: (libc)Limits for Files.
* pipe: (libc)Creating a Pipe.
* popen: (libc)Pipe to a Subprocess.
* _POSIX2_C_DEV: (libc)System Options.
* _POSIX2_C_VERSION: (libc)Version Supported.
* _POSIX2_FORT_DEV: (libc)System Options.
* _POSIX2_FORT_RUN: (libc)System Options.
* _POSIX2_LOCALEDEF: (libc)System Options.
* _POSIX2_SW_DEV: (libc)System Options.
* _POSIX_CHOWN_RESTRICTED: (libc)Options for Files.
* posix_fallocate64: (libc)Storage Allocation.
* posix_fallocate: (libc)Storage Allocation.
* _POSIX_JOB_CONTROL: (libc)System Options.
* posix_memalign: (libc)Aligned Memory Blocks.
* _POSIX_NO_TRUNC: (libc)Options for Files.
* _POSIX_SAVED_IDS: (libc)System Options.
* _POSIX_VDISABLE: (libc)Options for Files.
* _POSIX_VERSION: (libc)Version Supported.
* pow10f: (libc)Exponents and Logarithms.
* pow10: (libc)Exponents and Logarithms.
* pow10l: (libc)Exponents and Logarithms.
* powf: (libc)Exponents and Logarithms.
* pow: (libc)Exponents and Logarithms.
* powl: (libc)Exponents and Logarithms.
* __ppc_get_timebase_freq: (libc)PowerPC.
* __ppc_get_timebase: (libc)PowerPC.
* __ppc_mdoio: (libc)PowerPC.
* __ppc_mdoom: (libc)PowerPC.
* __ppc_set_ppr_low: (libc)PowerPC.
* __ppc_set_ppr_med_high: (libc)PowerPC.
* __ppc_set_ppr_med: (libc)PowerPC.
* __ppc_set_ppr_med_low: (libc)PowerPC.
* __ppc_set_ppr_very_low: (libc)PowerPC.
* __ppc_yield: (libc)PowerPC.
* pread64: (libc)I/O Primitives.
* pread: (libc)I/O Primitives.
* printf: (libc)Formatted Output Functions.
* printf_size_info: (libc)Predefined Printf Handlers.
* printf_size: (libc)Predefined Printf Handlers.
* psignal: (libc)Signal Messages.
* pthread_getattr_default_np: (libc)Default Thread Attributes.
* pthread_getspecific: (libc)Thread-specific Data.
* pthread_key_create: (libc)Thread-specific Data.
* pthread_key_delete: (libc)Thread-specific Data.
* pthread_setattr_default_np: (libc)Default Thread Attributes.
* pthread_setspecific: (libc)Thread-specific Data.
* P_tmpdir: (libc)Temporary Files.
* ptsname: (libc)Allocation.
* ptsname_r: (libc)Allocation.
* putchar: (libc)Simple Output.
* putchar_unlocked: (libc)Simple Output.
* putc: (libc)Simple Output.
* putc_unlocked: (libc)Simple Output.
* putenv: (libc)Environment Access.
* putpwent: (libc)Writing a User Entry.
* puts: (libc)Simple Output.
* pututline: (libc)Manipulating the Database.
* pututxline: (libc)XPG Functions.
* putwchar: (libc)Simple Output.
* putwchar_unlocked: (libc)Simple Output.
* putwc: (libc)Simple Output.
* putwc_unlocked: (libc)Simple Output.
* putw: (libc)Simple Output.
* pwrite64: (libc)I/O Primitives.
* pwrite: (libc)I/O Primitives.
* qecvt: (libc)System V Number Conversion.
* qecvt_r: (libc)System V Number Conversion.
* qfcvt: (libc)System V Number Conversion.
* qfcvt_r: (libc)System V Number Conversion.
* qgcvt: (libc)System V Number Conversion.
* qsort: (libc)Array Sort Function.
* raise: (libc)Signaling Yourself.
* rand: (libc)ISO Random.
* RAND_MAX: (libc)ISO Random.
* random: (libc)BSD Random.
* random_r: (libc)BSD Random.
* rand_r: (libc)ISO Random.
* rawmemchr: (libc)Search Functions.
* readdir64: (libc)Reading/Closing Directory.
* readdir64_r: (libc)Reading/Closing Directory.
* readdir: (libc)Reading/Closing Directory.
* readdir_r: (libc)Reading/Closing Directory.
* read: (libc)I/O Primitives.
* readlink: (libc)Symbolic Links.
* readv: (libc)Scatter-Gather.
* realloc: (libc)Changing Block Size.
* realpath: (libc)Symbolic Links.
* recvfrom: (libc)Receiving Datagrams.
* recv: (libc)Receiving Data.
* recvmsg: (libc)Receiving Datagrams.
* RE_DUP_MAX: (libc)General Limits.
* regcomp: (libc)POSIX Regexp Compilation.
* regerror: (libc)Regexp Cleanup.
* regexec: (libc)Matching POSIX Regexps.
* regfree: (libc)Regexp Cleanup.
* register_printf_function: (libc)Registering New Conversions.
* remainderf: (libc)Remainder Functions.
* remainder: (libc)Remainder Functions.
* remainderl: (libc)Remainder Functions.
* remove: (libc)Deleting Files.
* rename: (libc)Renaming Files.
* rewinddir: (libc)Random Access Directory.
* rewind: (libc)File Positioning.
* rindex: (libc)Search Functions.
* rintf: (libc)Rounding Functions.
* rint: (libc)Rounding Functions.
* rintl: (libc)Rounding Functions.
* RLIM_INFINITY: (libc)Limits on Resources.
* rmdir: (libc)Deleting Files.
* R_OK: (libc)Testing File Access.
* roundevenf: (libc)Rounding Functions.
* roundeven: (libc)Rounding Functions.
* roundevenl: (libc)Rounding Functions.
* roundf: (libc)Rounding Functions.
* round: (libc)Rounding Functions.
* roundl: (libc)Rounding Functions.
* rpmatch: (libc)Yes-or-No Questions.
* SA_NOCLDSTOP: (libc)Flags for Sigaction.
* SA_ONSTACK: (libc)Flags for Sigaction.
* SA_RESTART: (libc)Flags for Sigaction.
* sbrk: (libc)Resizing the Data Segment.
* scalbf: (libc)Normalization Functions.
* scalb: (libc)Normalization Functions.
* scalbl: (libc)Normalization Functions.
* scalblnf: (libc)Normalization Functions.
* scalbln: (libc)Normalization Functions.
* scalblnl: (libc)Normalization Functions.
* scalbnf: (libc)Normalization Functions.
* scalbn: (libc)Normalization Functions.
* scalbnl: (libc)Normalization Functions.
* scandir64: (libc)Scanning Directory Content.
* scandir: (libc)Scanning Directory Content.
* scanf: (libc)Formatted Input Functions.
* sched_getaffinity: (libc)CPU Affinity.
* sched_getparam: (libc)Basic Scheduling Functions.
* sched_get_priority_max: (libc)Basic Scheduling Functions.
* sched_get_priority_min: (libc)Basic Scheduling Functions.
* sched_getscheduler: (libc)Basic Scheduling Functions.
* sched_rr_get_interval: (libc)Basic Scheduling Functions.
* sched_setaffinity: (libc)CPU Affinity.
* sched_setparam: (libc)Basic Scheduling Functions.
* sched_setscheduler: (libc)Basic Scheduling Functions.
* sched_yield: (libc)Basic Scheduling Functions.
* secure_getenv: (libc)Environment Access.
* seed48: (libc)SVID Random.
* seed48_r: (libc)SVID Random.
* SEEK_CUR: (libc)File Positioning.
* seekdir: (libc)Random Access Directory.
* SEEK_END: (libc)File Positioning.
* SEEK_SET: (libc)File Positioning.
* select: (libc)Waiting for I/O.
* sem_close: (libc)Semaphores.
* semctl: (libc)Semaphores.
* sem_destroy: (libc)Semaphores.
* semget: (libc)Semaphores.
* sem_getvalue: (libc)Semaphores.
* sem_init: (libc)Semaphores.
* sem_open: (libc)Semaphores.
* semop: (libc)Semaphores.
* sem_post: (libc)Semaphores.
* semtimedop: (libc)Semaphores.
* sem_timedwait: (libc)Semaphores.
* sem_trywait: (libc)Semaphores.
* sem_unlink: (libc)Semaphores.
* sem_wait: (libc)Semaphores.
* send: (libc)Sending Data.
* sendmsg: (libc)Receiving Datagrams.
* sendto: (libc)Sending Datagrams.
* setbuffer: (libc)Controlling Buffering.
* setbuf: (libc)Controlling Buffering.
* setcontext: (libc)System V contexts.
* setdomainname: (libc)Host Identification.
* setegid: (libc)Setting Groups.
* setenv: (libc)Environment Access.
* seteuid: (libc)Setting User ID.
* setfsent: (libc)fstab.
* setgid: (libc)Setting Groups.
* setgrent: (libc)Scanning All Groups.
* setgroups: (libc)Setting Groups.
* sethostent: (libc)Host Names.
* sethostid: (libc)Host Identification.
* sethostname: (libc)Host Identification.
* setitimer: (libc)Setting an Alarm.
* setjmp: (libc)Non-Local Details.
* setkey: (libc)DES Encryption.
* setkey_r: (libc)DES Encryption.
* setlinebuf: (libc)Controlling Buffering.
* setlocale: (libc)Setting the Locale.
* setlogmask: (libc)setlogmask.
* setmntent: (libc)mtab.
* setnetent: (libc)Networks Database.
* setnetgrent: (libc)Lookup Netgroup.
* setpayloadf: (libc)FP Bit Twiddling.
* setpayload: (libc)FP Bit Twiddling.
* setpayloadl: (libc)FP Bit Twiddling.
* setpayloadsigf: (libc)FP Bit Twiddling.
* setpayloadsig: (libc)FP Bit Twiddling.
* setpayloadsigl: (libc)FP Bit Twiddling.
* setpgid: (libc)Process Group Functions.
* setpgrp: (libc)Process Group Functions.
* setpriority: (libc)Traditional Scheduling Functions.
* setprotoent: (libc)Protocols Database.
* setpwent: (libc)Scanning All Users.
* setregid: (libc)Setting Groups.
* setreuid: (libc)Setting User ID.
* setrlimit64: (libc)Limits on Resources.
* setrlimit: (libc)Limits on Resources.
* setservent: (libc)Services Database.
* setsid: (libc)Process Group Functions.
* setsockopt: (libc)Socket Option Functions.
* setstate: (libc)BSD Random.
* setstate_r: (libc)BSD Random.
* settimeofday: (libc)High-Resolution Calendar.
* setuid: (libc)Setting User ID.
* setutent: (libc)Manipulating the Database.
* setutxent: (libc)XPG Functions.
* setvbuf: (libc)Controlling Buffering.
* shm_open: (libc)Memory-mapped I/O.
* shm_unlink: (libc)Memory-mapped I/O.
* shutdown: (libc)Closing a Socket.
* S_IFMT: (libc)Testing File Type.
* SIGABRT: (libc)Program Error Signals.
* sigaction: (libc)Advanced Signal Handling.
* sigaddset: (libc)Signal Sets.
* SIGALRM: (libc)Alarm Signals.
* sigaltstack: (libc)Signal Stack.
* sigblock: (libc)BSD Signal Handling.
* SIGBUS: (libc)Program Error Signals.
* SIGCHLD: (libc)Job Control Signals.
* SIGCLD: (libc)Job Control Signals.
* SIGCONT: (libc)Job Control Signals.
* sigdelset: (libc)Signal Sets.
* sigemptyset: (libc)Signal Sets.
* SIGEMT: (libc)Program Error Signals.
* SIG_ERR: (libc)Basic Signal Handling.
* sigfillset: (libc)Signal Sets.
* SIGFPE: (libc)Program Error Signals.
* SIGHUP: (libc)Termination Signals.
* SIGILL: (libc)Program Error Signals.
* SIGINFO: (libc)Miscellaneous Signals.
* siginterrupt: (libc)BSD Signal Handling.
* SIGINT: (libc)Termination Signals.
* SIGIO: (libc)Asynchronous I/O Signals.
* SIGIOT: (libc)Program Error Signals.
* sigismember: (libc)Signal Sets.
* SIGKILL: (libc)Termination Signals.
* siglongjmp: (libc)Non-Local Exits and Signals.
* SIGLOST: (libc)Operation Error Signals.
* sigmask: (libc)BSD Signal Handling.
* signal: (libc)Basic Signal Handling.
* signbit: (libc)FP Bit Twiddling.
* significandf: (libc)Normalization Functions.
* significand: (libc)Normalization Functions.
* significandl: (libc)Normalization Functions.
* sigpause: (libc)BSD Signal Handling.
* sigpending: (libc)Checking for Pending Signals.
* SIGPIPE: (libc)Operation Error Signals.
* SIGPOLL: (libc)Asynchronous I/O Signals.
* sigprocmask: (libc)Process Signal Mask.
* SIGPROF: (libc)Alarm Signals.
* SIGQUIT: (libc)Termination Signals.
* SIGSEGV: (libc)Program Error Signals.
* sigsetjmp: (libc)Non-Local Exits and Signals.
* sigsetmask: (libc)BSD Signal Handling.
* sigstack: (libc)Signal Stack.
* SIGSTOP: (libc)Job Control Signals.
* sigsuspend: (libc)Sigsuspend.
* SIGSYS: (libc)Program Error Signals.
* SIGTERM: (libc)Termination Signals.
* SIGTRAP: (libc)Program Error Signals.
* SIGTSTP: (libc)Job Control Signals.
* SIGTTIN: (libc)Job Control Signals.
* SIGTTOU: (libc)Job Control Signals.
* SIGURG: (libc)Asynchronous I/O Signals.
* SIGUSR1: (libc)Miscellaneous Signals.
* SIGUSR2: (libc)Miscellaneous Signals.
* SIGVTALRM: (libc)Alarm Signals.
* SIGWINCH: (libc)Miscellaneous Signals.
* SIGXCPU: (libc)Operation Error Signals.
* SIGXFSZ: (libc)Operation Error Signals.
* sincosf: (libc)Trig Functions.
* sincos: (libc)Trig Functions.
* sincosl: (libc)Trig Functions.
* sinf: (libc)Trig Functions.
* sinhf: (libc)Hyperbolic Functions.
* sinh: (libc)Hyperbolic Functions.
* sinhl: (libc)Hyperbolic Functions.
* sin: (libc)Trig Functions.
* sinl: (libc)Trig Functions.
* S_ISBLK: (libc)Testing File Type.
* S_ISCHR: (libc)Testing File Type.
* S_ISDIR: (libc)Testing File Type.
* S_ISFIFO: (libc)Testing File Type.
* S_ISLNK: (libc)Testing File Type.
* S_ISREG: (libc)Testing File Type.
* S_ISSOCK: (libc)Testing File Type.
* sleep: (libc)Sleeping.
* SNANF: (libc)Infinity and NaN.
* SNAN: (libc)Infinity and NaN.
* SNANL: (libc)Infinity and NaN.
* snprintf: (libc)Formatted Output Functions.
* SOCK_DGRAM: (libc)Communication Styles.
* socket: (libc)Creating a Socket.
* socketpair: (libc)Socket Pairs.
* SOCK_RAW: (libc)Communication Styles.
* SOCK_RDM: (libc)Communication Styles.
* SOCK_SEQPACKET: (libc)Communication Styles.
* SOCK_STREAM: (libc)Communication Styles.
* SOL_SOCKET: (libc)Socket-Level Options.
* sprintf: (libc)Formatted Output Functions.
* sqrtf: (libc)Exponents and Logarithms.
* sqrt: (libc)Exponents and Logarithms.
* sqrtl: (libc)Exponents and Logarithms.
* srand48: (libc)SVID Random.
* srand48_r: (libc)SVID Random.
* srand: (libc)ISO Random.
* srandom: (libc)BSD Random.
* srandom_r: (libc)BSD Random.
* sscanf: (libc)Formatted Input Functions.
* ssignal: (libc)Basic Signal Handling.
* SSIZE_MAX: (libc)General Limits.
* stat64: (libc)Reading Attributes.
* stat: (libc)Reading Attributes.
* stime: (libc)Simple Calendar Time.
* stpcpy: (libc)Copying Strings and Arrays.
* stpncpy: (libc)Truncating Strings.
* strcasecmp: (libc)String/Array Comparison.
* strcasestr: (libc)Search Functions.
* strcat: (libc)Concatenating Strings.
* strchr: (libc)Search Functions.
* strchrnul: (libc)Search Functions.
* strcmp: (libc)String/Array Comparison.
* strcoll: (libc)Collation Functions.
* strcpy: (libc)Copying Strings and Arrays.
* strcspn: (libc)Search Functions.
* strdupa: (libc)Copying Strings and Arrays.
* strdup: (libc)Copying Strings and Arrays.
* STREAM_MAX: (libc)General Limits.
* strerror: (libc)Error Messages.
* strerror_r: (libc)Error Messages.
* strfmon: (libc)Formatting Numbers.
* strfromd: (libc)Printing of Floats.
* strfromf: (libc)Printing of Floats.
* strfroml: (libc)Printing of Floats.
* strfry: (libc)strfry.
* strftime: (libc)Formatting Calendar Time.
* strlen: (libc)String Length.
* strncasecmp: (libc)String/Array Comparison.
* strncat: (libc)Truncating Strings.
* strncmp: (libc)String/Array Comparison.
* strncpy: (libc)Truncating Strings.
* strndupa: (libc)Truncating Strings.
* strndup: (libc)Truncating Strings.
* strnlen: (libc)String Length.
* strpbrk: (libc)Search Functions.
* strptime: (libc)Low-Level Time String Parsing.
* strrchr: (libc)Search Functions.
* strsep: (libc)Finding Tokens in a String.
* strsignal: (libc)Signal Messages.
* strspn: (libc)Search Functions.
* strstr: (libc)Search Functions.
* strtod: (libc)Parsing of Floats.
* strtof: (libc)Parsing of Floats.
* strtoimax: (libc)Parsing of Integers.
* strtok: (libc)Finding Tokens in a String.
* strtok_r: (libc)Finding Tokens in a String.
* strtold: (libc)Parsing of Floats.
* strtol: (libc)Parsing of Integers.
* strtoll: (libc)Parsing of Integers.
* strtoq: (libc)Parsing of Integers.
* strtoul: (libc)Parsing of Integers.
* strtoull: (libc)Parsing of Integers.
* strtoumax: (libc)Parsing of Integers.
* strtouq: (libc)Parsing of Integers.
* strverscmp: (libc)String/Array Comparison.
* strxfrm: (libc)Collation Functions.
* stty: (libc)BSD Terminal Modes.
* S_TYPEISMQ: (libc)Testing File Type.
* S_TYPEISSEM: (libc)Testing File Type.
* S_TYPEISSHM: (libc)Testing File Type.
* SUN_LEN: (libc)Local Namespace Details.
* swapcontext: (libc)System V contexts.
* swprintf: (libc)Formatted Output Functions.
* swscanf: (libc)Formatted Input Functions.
* symlink: (libc)Symbolic Links.
* sync: (libc)Synchronizing I/O.
* syscall: (libc)System Calls.
* sysconf: (libc)Sysconf Definition.
* sysctl: (libc)System Parameters.
* syslog: (libc)syslog; vsyslog.
* system: (libc)Running a Command.
* sysv_signal: (libc)Basic Signal Handling.
* tanf: (libc)Trig Functions.
* tanhf: (libc)Hyperbolic Functions.
* tanh: (libc)Hyperbolic Functions.
* tanhl: (libc)Hyperbolic Functions.
* tan: (libc)Trig Functions.
* tanl: (libc)Trig Functions.
* tcdrain: (libc)Line Control.
* tcflow: (libc)Line Control.
* tcflush: (libc)Line Control.
* tcgetattr: (libc)Mode Functions.
* tcgetpgrp: (libc)Terminal Access Functions.
* tcgetsid: (libc)Terminal Access Functions.
* tcsendbreak: (libc)Line Control.
* tcsetattr: (libc)Mode Functions.
* tcsetpgrp: (libc)Terminal Access Functions.
* tdelete: (libc)Tree Search Function.
* tdestroy: (libc)Tree Search Function.
* telldir: (libc)Random Access Directory.
* tempnam: (libc)Temporary Files.
* textdomain: (libc)Locating gettext catalog.
* tfind: (libc)Tree Search Function.
* tgammaf: (libc)Special Functions.
* tgamma: (libc)Special Functions.
* tgammal: (libc)Special Functions.
* timegm: (libc)Broken-down Time.
* time: (libc)Simple Calendar Time.
* timelocal: (libc)Broken-down Time.
* times: (libc)Processor Time.
* tmpfile64: (libc)Temporary Files.
* tmpfile: (libc)Temporary Files.
* TMP_MAX: (libc)Temporary Files.
* tmpnam: (libc)Temporary Files.
* tmpnam_r: (libc)Temporary Files.
* toascii: (libc)Case Conversion.
* _tolower: (libc)Case Conversion.
* tolower: (libc)Case Conversion.
* TOSTOP: (libc)Local Modes.
* totalorderf: (libc)FP Comparison Functions.
* totalorder: (libc)FP Comparison Functions.
* totalorderl: (libc)FP Comparison Functions.
* totalordermagf: (libc)FP Comparison Functions.
* totalordermag: (libc)FP Comparison Functions.
* totalordermagl: (libc)FP Comparison Functions.
* _toupper: (libc)Case Conversion.
* toupper: (libc)Case Conversion.
* towctrans: (libc)Wide Character Case Conversion.
* towlower: (libc)Wide Character Case Conversion.
* towupper: (libc)Wide Character Case Conversion.
* truncate64: (libc)File Size.
* truncate: (libc)File Size.
* truncf: (libc)Rounding Functions.
* trunc: (libc)Rounding Functions.
* truncl: (libc)Rounding Functions.
* tsearch: (libc)Tree Search Function.
* ttyname: (libc)Is It a Terminal.
* ttyname_r: (libc)Is It a Terminal.
* twalk: (libc)Tree Search Function.
* TZNAME_MAX: (libc)General Limits.
* tzset: (libc)Time Zone Functions.
* ufromfpf: (libc)Rounding Functions.
* ufromfp: (libc)Rounding Functions.
* ufromfpl: (libc)Rounding Functions.
* ufromfpxf: (libc)Rounding Functions.
* ufromfpx: (libc)Rounding Functions.
* ufromfpxl: (libc)Rounding Functions.
* ulimit: (libc)Limits on Resources.
* umask: (libc)Setting Permissions.
* umount2: (libc)Mount-Unmount-Remount.
* umount: (libc)Mount-Unmount-Remount.
* uname: (libc)Platform Type.
* ungetc: (libc)How Unread.
* ungetwc: (libc)How Unread.
* unlink: (libc)Deleting Files.
* unlockpt: (libc)Allocation.
* unsetenv: (libc)Environment Access.
* updwtmp: (libc)Manipulating the Database.
* utime: (libc)File Times.
* utimes: (libc)File Times.
* utmpname: (libc)Manipulating the Database.
* utmpxname: (libc)XPG Functions.
* va_arg: (libc)Argument Macros.
* __va_copy: (libc)Argument Macros.
* va_copy: (libc)Argument Macros.
* va_end: (libc)Argument Macros.
* valloc: (libc)Aligned Memory Blocks.
* vasprintf: (libc)Variable Arguments Output.
* va_start: (libc)Argument Macros.
* VDISCARD: (libc)Other Special.
* VDSUSP: (libc)Signal Characters.
* VEOF: (libc)Editing Characters.
* VEOL2: (libc)Editing Characters.
* VEOL: (libc)Editing Characters.
* VERASE: (libc)Editing Characters.
* verr: (libc)Error Messages.
* verrx: (libc)Error Messages.
* versionsort64: (libc)Scanning Directory Content.
* versionsort: (libc)Scanning Directory Content.
* vfork: (libc)Creating a Process.
* vfprintf: (libc)Variable Arguments Output.
* vfscanf: (libc)Variable Arguments Input.
* vfwprintf: (libc)Variable Arguments Output.
* vfwscanf: (libc)Variable Arguments Input.
* VINTR: (libc)Signal Characters.
* VKILL: (libc)Editing Characters.
* vlimit: (libc)Limits on Resources.
* VLNEXT: (libc)Other Special.
* VMIN: (libc)Noncanonical Input.
* vprintf: (libc)Variable Arguments Output.
* VQUIT: (libc)Signal Characters.
* VREPRINT: (libc)Editing Characters.
* vscanf: (libc)Variable Arguments Input.
* vsnprintf: (libc)Variable Arguments Output.
* vsprintf: (libc)Variable Arguments Output.
* vsscanf: (libc)Variable Arguments Input.
* VSTART: (libc)Start/Stop Characters.
* VSTATUS: (libc)Other Special.
* VSTOP: (libc)Start/Stop Characters.
* VSUSP: (libc)Signal Characters.
* vswprintf: (libc)Variable Arguments Output.
* vswscanf: (libc)Variable Arguments Input.
* vsyslog: (libc)syslog; vsyslog.
* VTIME: (libc)Noncanonical Input.
* vtimes: (libc)Resource Usage.
* vwarn: (libc)Error Messages.
* vwarnx: (libc)Error Messages.
* VWERASE: (libc)Editing Characters.
* vwprintf: (libc)Variable Arguments Output.
* vwscanf: (libc)Variable Arguments Input.
* wait3: (libc)BSD Wait Functions.
* wait4: (libc)Process Completion.
* wait: (libc)Process Completion.
* waitpid: (libc)Process Completion.
* warn: (libc)Error Messages.
* warnx: (libc)Error Messages.
* WCHAR_MAX: (libc)Extended Char Intro.
* WCHAR_MIN: (libc)Extended Char Intro.
* WCOREDUMP: (libc)Process Completion Status.
* wcpcpy: (libc)Copying Strings and Arrays.
* wcpncpy: (libc)Truncating Strings.
* wcrtomb: (libc)Converting a Character.
* wcscasecmp: (libc)String/Array Comparison.
* wcscat: (libc)Concatenating Strings.
* wcschr: (libc)Search Functions.
* wcschrnul: (libc)Search Functions.
* wcscmp: (libc)String/Array Comparison.
* wcscoll: (libc)Collation Functions.
* wcscpy: (libc)Copying Strings and Arrays.
* wcscspn: (libc)Search Functions.
* wcsdup: (libc)Copying Strings and Arrays.
* wcsftime: (libc)Formatting Calendar Time.
* wcslen: (libc)String Length.
* wcsncasecmp: (libc)String/Array Comparison.
* wcsncat: (libc)Truncating Strings.
* wcsncmp: (libc)String/Array Comparison.
* wcsncpy: (libc)Truncating Strings.
* wcsnlen: (libc)String Length.
* wcsnrtombs: (libc)Converting Strings.
* wcspbrk: (libc)Search Functions.
* wcsrchr: (libc)Search Functions.
* wcsrtombs: (libc)Converting Strings.
* wcsspn: (libc)Search Functions.
* wcsstr: (libc)Search Functions.
* wcstod: (libc)Parsing of Floats.
* wcstof: (libc)Parsing of Floats.
* wcstoimax: (libc)Parsing of Integers.
* wcstok: (libc)Finding Tokens in a String.
* wcstold: (libc)Parsing of Floats.
* wcstol: (libc)Parsing of Integers.
* wcstoll: (libc)Parsing of Integers.
* wcstombs: (libc)Non-reentrant String Conversion.
* wcstoq: (libc)Parsing of Integers.
* wcstoul: (libc)Parsing of Integers.
* wcstoull: (libc)Parsing of Integers.
* wcstoumax: (libc)Parsing of Integers.
* wcstouq: (libc)Parsing of Integers.
* wcswcs: (libc)Search Functions.
* wcsxfrm: (libc)Collation Functions.
* wctob: (libc)Converting a Character.
* wctomb: (libc)Non-reentrant Character Conversion.
* wctrans: (libc)Wide Character Case Conversion.
* wctype: (libc)Classification of Wide Characters.
* WEOF: (libc)EOF and Errors.
* WEOF: (libc)Extended Char Intro.
* WEXITSTATUS: (libc)Process Completion Status.
* WIFEXITED: (libc)Process Completion Status.
* WIFSIGNALED: (libc)Process Completion Status.
* WIFSTOPPED: (libc)Process Completion Status.
* wmemchr: (libc)Search Functions.
* wmemcmp: (libc)String/Array Comparison.
* wmemcpy: (libc)Copying Strings and Arrays.
* wmemmove: (libc)Copying Strings and Arrays.
* wmempcpy: (libc)Copying Strings and Arrays.
* wmemset: (libc)Copying Strings and Arrays.
* W_OK: (libc)Testing File Access.
* wordexp: (libc)Calling Wordexp.
* wordfree: (libc)Calling Wordexp.
* wprintf: (libc)Formatted Output Functions.
* write: (libc)I/O Primitives.
* writev: (libc)Scatter-Gather.
* wscanf: (libc)Formatted Input Functions.
* WSTOPSIG: (libc)Process Completion Status.
* WTERMSIG: (libc)Process Completion Status.
* X_OK: (libc)Testing File Access.
* y0f: (libc)Special Functions.
* y0: (libc)Special Functions.
* y0l: (libc)Special Functions.
* y1f: (libc)Special Functions.
* y1: (libc)Special Functions.
* y1l: (libc)Special Functions.
* ynf: (libc)Special Functions.
* yn: (libc)Special Functions.
* ynl: (libc)Special Functions.
END-INFO-DIR-ENTRY



File: libc.info,  Node: Searching and Sorting,  Next: Pattern Matching,  Prev: Message Translation,  Up: Top

9 Searching and Sorting
***********************

This chapter describes functions for searching and sorting arrays of
arbitrary objects.  You pass the appropriate comparison function to be
applied as an argument, along with the size of the objects in the array
and the total number of elements.

* Menu:

* Comparison Functions::        Defining how to compare two objects.
				 Since the sort and search facilities
                                 are general, you have to specify the
                                 ordering.
* Array Search Function::       The ‘bsearch’ function.
* Array Sort Function::         The ‘qsort’ function.
* Search/Sort Example::         An example program.
* Hash Search Function::        The ‘hsearch’ function.
* Tree Search Function::        The ‘tsearch’ function.


File: libc.info,  Node: Comparison Functions,  Next: Array Search Function,  Up: Searching and Sorting

9.1 Defining the Comparison Function
====================================

In order to use the sorted array library functions, you have to describe
how to compare the elements of the array.

   To do this, you supply a comparison function to compare two elements
of the array.  The library will call this function, passing as arguments
pointers to two array elements to be compared.  Your comparison function
should return a value the way ‘strcmp’ (*note String/Array Comparison::)
does: negative if the first argument is “less” than the second, zero if
they are “equal”, and positive if the first argument is “greater”.

   Here is an example of a comparison function which works with an array
of numbers of type ‘double’:

     int
     compare_doubles (const void *a, const void *b)
     {
       const double *da = (const double *) a;
       const double *db = (const double *) b;

       return (*da > *db) - (*da < *db);
     }

   The header file ‘stdlib.h’ defines a name for the data type of
comparison functions.  This type is a GNU extension.

     int comparison_fn_t (const void *, const void *);


File: libc.info,  Node: Array Search Function,  Next: Array Sort Function,  Prev: Comparison Functions,  Up: Searching and Sorting

9.2 Array Search Function
=========================

Generally searching for a specific element in an array means that
potentially all elements must be checked.  The GNU C Library contains
functions to perform linear search.  The prototypes for the following
two functions can be found in ‘search.h’.

 -- Function: void * lfind (const void *KEY, const void *BASE, size_t
          *NMEMB, size_t SIZE, comparison_fn_t COMPAR)
     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     The ‘lfind’ function searches in the array with ‘*NMEMB’ elements
     of SIZE bytes pointed to by BASE for an element which matches the
     one pointed to by KEY.  The function pointed to by COMPAR is used
     to decide whether two elements match.

     The return value is a pointer to the matching element in the array
     starting at BASE if it is found.  If no matching element is
     available ‘NULL’ is returned.

     The mean runtime of this function is ‘*NMEMB’/2.  This function
     should only be used if elements often get added to or deleted from
     the array in which case it might not be useful to sort the array
     before searching.

 -- Function: void * lsearch (const void *KEY, void *BASE, size_t
          *NMEMB, size_t SIZE, comparison_fn_t COMPAR)
     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     The ‘lsearch’ function is similar to the ‘lfind’ function.  It
     searches the given array for an element and returns it if found.
     The difference is that if no matching element is found the
     ‘lsearch’ function adds the object pointed to by KEY (with a size
     of SIZE bytes) at the end of the array and it increments the value
     of ‘*NMEMB’ to reflect this addition.

     This means for the caller that if it is not sure that the array
     contains the element one is searching for the memory allocated for
     the array starting at BASE must have room for at least SIZE more
     bytes.  If one is sure the element is in the array it is better to
     use ‘lfind’ so having more room in the array is always necessary
     when calling ‘lsearch’.

   To search a sorted array for an element matching the key, use the
‘bsearch’ function.  The prototype for this function is in the header
file ‘stdlib.h’.

 -- Function: void * bsearch (const void *KEY, const void *ARRAY, size_t
          COUNT, size_t SIZE, comparison_fn_t COMPARE)
     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     The ‘bsearch’ function searches the sorted array ARRAY for an
     object that is equivalent to KEY.  The array contains COUNT
     elements, each of which is of size SIZE bytes.

     The COMPARE function is used to perform the comparison.  This
     function is called with two pointer arguments and should return an
     integer less than, equal to, or greater than zero corresponding to
     whether its first argument is considered less than, equal to, or
     greater than its second argument.  The elements of the ARRAY must
     already be sorted in ascending order according to this comparison
     function.

     The return value is a pointer to the matching array element, or a
     null pointer if no match is found.  If the array contains more than
     one element that matches, the one that is returned is unspecified.

     This function derives its name from the fact that it is implemented
     using the binary search algorithm.


File: libc.info,  Node: Array Sort Function,  Next: Search/Sort Example,  Prev: Array Search Function,  Up: Searching and Sorting

9.3 Array Sort Function
=======================

To sort an array using an arbitrary comparison function, use the ‘qsort’
function.  The prototype for this function is in ‘stdlib.h’.

 -- Function: void qsort (void *ARRAY, size_t COUNT, size_t SIZE,
          comparison_fn_t COMPARE)
     Preliminary: | MT-Safe | AS-Safe | AC-Unsafe corrupt | *Note POSIX
     Safety Concepts::.

     The ‘qsort’ function sorts the array ARRAY.  The array contains
     COUNT elements, each of which is of size SIZE.

     The COMPARE function is used to perform the comparison on the array
     elements.  This function is called with two pointer arguments and
     should return an integer less than, equal to, or greater than zero
     corresponding to whether its first argument is considered less
     than, equal to, or greater than its second argument.

     *Warning:* If two objects compare as equal, their order after
     sorting is unpredictable.  That is to say, the sorting is not
     stable.  This can make a difference when the comparison considers
     only part of the elements.  Two elements with the same sort key may
     differ in other respects.

     Although the object addresses passed to the comparison function lie
     within the array, they need not correspond with the original
     locations of those objects because the sorting algorithm may swap
     around objects in the array before making some comparisons.  The
     only way to perform a stable sort with ‘qsort’ is to first augment
     the objects with a monotonic counter of some kind.

     Here is a simple example of sorting an array of doubles in
     numerical order, using the comparison function defined above (*note
     Comparison Functions::):

          {
            double *array;
            int size;
            …
            qsort (array, size, sizeof (double), compare_doubles);
          }

     The ‘qsort’ function derives its name from the fact that it was
     originally implemented using the “quick sort” algorithm.

     The implementation of ‘qsort’ in this library might not be an
     in-place sort and might thereby use an extra amount of memory to
     store the array.


File: libc.info,  Node: Search/Sort Example,  Next: Hash Search Function,  Prev: Array Sort Function,  Up: Searching and Sorting

9.4 Searching and Sorting Example
=================================

Here is an example showing the use of ‘qsort’ and ‘bsearch’ with an
array of structures.  The objects in the array are sorted by comparing
their ‘name’ fields with the ‘strcmp’ function.  Then, we can look up
individual objects based on their names.


     #include <stdlib.h>
     #include <stdio.h>
     #include <string.h>

     /* Define an array of critters to sort. */

     struct critter
       {
         const char *name;
         const char *species;
       };

     struct critter muppets[] =
       {
         {"Kermit", "frog"},
         {"Piggy", "pig"},
         {"Gonzo", "whatever"},
         {"Fozzie", "bear"},
         {"Sam", "eagle"},
         {"Robin", "frog"},
         {"Animal", "animal"},
         {"Camilla", "chicken"},
         {"Sweetums", "monster"},
         {"Dr. Strangepork", "pig"},
         {"Link Hogthrob", "pig"},
         {"Zoot", "human"},
         {"Dr. Bunsen Honeydew", "human"},
         {"Beaker", "human"},
         {"Swedish Chef", "human"}
       };

     int count = sizeof (muppets) / sizeof (struct critter);



     /* This is the comparison function used for sorting and searching. */

     int
     critter_cmp (const void *v1, const void *v2)
     {
       const struct critter *c1 = v1;
       const struct critter *c2 = v2;

       return strcmp (c1->name, c2->name);
     }


     /* Print information about a critter. */

     void
     print_critter (const struct critter *c)
     {
       printf ("%s, the %s\n", c->name, c->species);
     }


     /* Do the lookup into the sorted array. */

     void
     find_critter (const char *name)
     {
       struct critter target, *result;
       target.name = name;
       result = bsearch (&target, muppets, count, sizeof (struct critter),
                         critter_cmp);
       if (result)
         print_critter (result);
       else
         printf ("Couldn't find %s.\n", name);
     }

     /* Main program. */

     int
     main (void)
     {
       int i;

       for (i = 0; i < count; i++)
         print_critter (&muppets[i]);
       printf ("\n");

       qsort (muppets, count, sizeof (struct critter), critter_cmp);

       for (i = 0; i < count; i++)
         print_critter (&muppets[i]);
       printf ("\n");

       find_critter ("Kermit");
       find_critter ("Gonzo");
       find_critter ("Janice");

       return 0;
     }

   The output from this program looks like:

     Kermit, the frog
     Piggy, the pig
     Gonzo, the whatever
     Fozzie, the bear
     Sam, the eagle
     Robin, the frog
     Animal, the animal
     Camilla, the chicken
     Sweetums, the monster
     Dr. Strangepork, the pig
     Link Hogthrob, the pig
     Zoot, the human
     Dr. Bunsen Honeydew, the human
     Beaker, the human
     Swedish Chef, the human

     Animal, the animal
     Beaker, the human
     Camilla, the chicken
     Dr. Bunsen Honeydew, the human
     Dr. Strangepork, the pig
     Fozzie, the bear
     Gonzo, the whatever
     Kermit, the frog
     Link Hogthrob, the pig
     Piggy, the pig
     Robin, the frog
     Sam, the eagle
     Swedish Chef, the human
     Sweetums, the monster
     Zoot, the human

     Kermit, the frog
     Gonzo, the whatever
     Couldn't find Janice.


File: libc.info,  Node: Hash Search Function,  Next: Tree Search Function,  Prev: Search/Sort Example,  Up: Searching and Sorting

9.5 The ‘hsearch’ function.
===========================

The functions mentioned so far in this chapter are for searching in a
sorted or unsorted array.  There are other methods to organize
information which later should be searched.  The costs of insert, delete
and search differ.  One possible implementation is using hashing tables.
The following functions are declared in the header file ‘search.h’.

 -- Function: int hcreate (size_t NEL)
     Preliminary: | MT-Unsafe race:hsearch | AS-Unsafe heap | AC-Unsafe
     corrupt mem | *Note POSIX Safety Concepts::.

     The ‘hcreate’ function creates a hashing table which can contain at
     least NEL elements.  There is no possibility to grow this table so
     it is necessary to choose the value for NEL wisely.  The method
     used to implement this function might make it necessary to make the
     number of elements in the hashing table larger than the expected
     maximal number of elements.  Hashing tables usually work
     inefficiently if they are filled 80% or more.  The constant access
     time guaranteed by hashing can only be achieved if few collisions
     exist.  See Knuth’s “The Art of Computer Programming, Part 3:
     Searching and Sorting” for more information.

     The weakest aspect of this function is that there can be at most
     one hashing table used through the whole program.  The table is
     allocated in local memory out of control of the programmer.  As an
     extension the GNU C Library provides an additional set of functions
     with a reentrant interface which provides a similar interface but
     which allows keeping arbitrarily many hashing tables.

     It is possible to use more than one hashing table in the program
     run if the former table is first destroyed by a call to ‘hdestroy’.

     The function returns a non-zero value if successful.  If it returns
     zero, something went wrong.  This could either mean there is
     already a hashing table in use or the program ran out of memory.

 -- Function: void hdestroy (void)
     Preliminary: | MT-Unsafe race:hsearch | AS-Unsafe heap | AC-Unsafe
     corrupt mem | *Note POSIX Safety Concepts::.

     The ‘hdestroy’ function can be used to free all the resources
     allocated in a previous call of ‘hcreate’.  After a call to this
     function it is again possible to call ‘hcreate’ and allocate a new
     table with possibly different size.

     It is important to remember that the elements contained in the
     hashing table at the time ‘hdestroy’ is called are _not_ freed by
     this function.  It is the responsibility of the program code to
     free those strings (if necessary at all).  Freeing all the element
     memory is not possible without extra, separately kept information
     since there is no function to iterate through all available
     elements in the hashing table.  If it is really necessary to free a
     table and all elements the programmer has to keep a list of all
     table elements and before calling ‘hdestroy’ s/he has to free all
     element’s data using this list.  This is a very unpleasant
     mechanism and it also shows that this kind of hashing table is
     mainly meant for tables which are created once and used until the
     end of the program run.

   Entries of the hashing table and keys for the search are defined
using this type:

 -- Data type: struct ENTRY
     Both elements of this structure are pointers to zero-terminated
     strings.  This is a limiting restriction of the functionality of
     the ‘hsearch’ functions.  They can only be used for data sets which
     use the NUL character always and solely to terminate the records.
     It is not possible to handle general binary data.

     ‘char *key’
          Pointer to a zero-terminated string of characters describing
          the key for the search or the element in the hashing table.
     ‘char *data’
          Pointer to a zero-terminated string of characters describing
          the data.  If the functions will be called only for searching
          an existing entry this element might stay undefined since it
          is not used.

 -- Function: ENTRY * hsearch (ENTRY ITEM, ACTION ACTION)
     Preliminary: | MT-Unsafe race:hsearch | AS-Unsafe | AC-Unsafe
     corrupt/action==ENTER | *Note POSIX Safety Concepts::.

     To search in a hashing table created using ‘hcreate’ the ‘hsearch’
     function must be used.  This function can perform a simple search
     for an element (if ACTION has the value ‘FIND’) or it can
     alternatively insert the key element into the hashing table.
     Entries are never replaced.

     The key is denoted by a pointer to an object of type ‘ENTRY’.  For
     locating the corresponding position in the hashing table only the
     ‘key’ element of the structure is used.

     If an entry with a matching key is found the ACTION parameter is
     irrelevant.  The found entry is returned.  If no matching entry is
     found and the ACTION parameter has the value ‘FIND’ the function
     returns a ‘NULL’ pointer.  If no entry is found and the ACTION
     parameter has the value ‘ENTER’ a new entry is added to the hashing
     table which is initialized with the parameter ITEM.  A pointer to
     the newly added entry is returned.

   As mentioned before, the hashing table used by the functions
described so far is global and there can be at any time at most one
hashing table in the program.  A solution is to use the following
functions which are a GNU extension.  All have in common that they
operate on a hashing table which is described by the content of an
object of the type ‘struct hsearch_data’.  This type should be treated
as opaque, none of its members should be changed directly.

 -- Function: int hcreate_r (size_t NEL, struct hsearch_data *HTAB)
     Preliminary: | MT-Safe race:htab | AS-Unsafe heap | AC-Unsafe
     corrupt mem | *Note POSIX Safety Concepts::.

     The ‘hcreate_r’ function initializes the object pointed to by HTAB
     to contain a hashing table with at least NEL elements.  So this
     function is equivalent to the ‘hcreate’ function except that the
     initialized data structure is controlled by the user.

     This allows having more than one hashing table at one time.  The
     memory necessary for the ‘struct hsearch_data’ object can be
     allocated dynamically.  It must be initialized with zero before
     calling this function.

     The return value is non-zero if the operation was successful.  If
     the return value is zero, something went wrong, which probably
     means the program ran out of memory.

 -- Function: void hdestroy_r (struct hsearch_data *HTAB)
     Preliminary: | MT-Safe race:htab | AS-Unsafe heap | AC-Unsafe
     corrupt mem | *Note POSIX Safety Concepts::.

     The ‘hdestroy_r’ function frees all resources allocated by the
     ‘hcreate_r’ function for this very same object HTAB.  As for
     ‘hdestroy’ it is the program’s responsibility to free the strings
     for the elements of the table.

 -- Function: int hsearch_r (ENTRY ITEM, ACTION ACTION, ENTRY **RETVAL,
          struct hsearch_data *HTAB)
     Preliminary: | MT-Safe race:htab | AS-Safe | AC-Unsafe
     corrupt/action==ENTER | *Note POSIX Safety Concepts::.

     The ‘hsearch_r’ function is equivalent to ‘hsearch’.  The meaning
     of the first two arguments is identical.  But instead of operating
     on a single global hashing table the function works on the table
     described by the object pointed to by HTAB (which is initialized by
     a call to ‘hcreate_r’).

     Another difference to ‘hcreate’ is that the pointer to the found
     entry in the table is not the return value of the function.  It is
     returned by storing it in a pointer variable pointed to by the
     RETVAL parameter.  The return value of the function is an integer
     value indicating success if it is non-zero and failure if it is
     zero.  In the latter case the global variable ERRNO signals the
     reason for the failure.

     ‘ENOMEM’
          The table is filled and ‘hsearch_r’ was called with a so far
          unknown key and ACTION set to ‘ENTER’.
     ‘ESRCH’
          The ACTION parameter is ‘FIND’ and no corresponding element is
          found in the table.


File: libc.info,  Node: Tree Search Function,  Prev: Hash Search Function,  Up: Searching and Sorting

9.6 The ‘tsearch’ function.
===========================

Another common form to organize data for efficient search is to use
trees.  The ‘tsearch’ function family provides a nice interface to
functions to organize possibly large amounts of data by providing a mean
access time proportional to the logarithm of the number of elements.
The GNU C Library implementation even guarantees that this bound is
never exceeded even for input data which cause problems for simple
binary tree implementations.

   The functions described in the chapter are all described in the System V
and X/Open specifications and are therefore quite portable.

   In contrast to the ‘hsearch’ functions the ‘tsearch’ functions can be
used with arbitrary data and not only zero-terminated strings.

   The ‘tsearch’ functions have the advantage that no function to
initialize data structures is necessary.  A simple pointer of type ‘void
*’ initialized to ‘NULL’ is a valid tree and can be extended or
searched.  The prototypes for these functions can be found in the header
file ‘search.h’.

 -- Function: void * tsearch (const void *KEY, void **ROOTP,
          comparison_fn_t COMPAR)
     Preliminary: | MT-Safe race:rootp | AS-Unsafe heap | AC-Unsafe
     corrupt mem | *Note POSIX Safety Concepts::.

     The ‘tsearch’ function searches in the tree pointed to by ‘*ROOTP’
     for an element matching KEY.  The function pointed to by COMPAR is
     used to determine whether two elements match.  *Note Comparison
     Functions::, for a specification of the functions which can be used
     for the COMPAR parameter.

     If the tree does not contain a matching entry the KEY value will be
     added to the tree.  ‘tsearch’ does not make a copy of the object
     pointed to by KEY (how could it since the size is unknown).
     Instead it adds a reference to this object which means the object
     must be available as long as the tree data structure is used.

     The tree is represented by a pointer to a pointer since it is
     sometimes necessary to change the root node of the tree.  So it
     must not be assumed that the variable pointed to by ROOTP has the
     same value after the call.  This also shows that it is not safe to
     call the ‘tsearch’ function more than once at the same time using
     the same tree.  It is no problem to run it more than once at a time
     on different trees.

     The return value is a pointer to the matching element in the tree.
     If a new element was created the pointer points to the new data
     (which is in fact KEY).  If an entry had to be created and the
     program ran out of space ‘NULL’ is returned.

 -- Function: void * tfind (const void *KEY, void *const *ROOTP,
          comparison_fn_t COMPAR)
     Preliminary: | MT-Safe race:rootp | AS-Safe | AC-Safe | *Note POSIX
     Safety Concepts::.

     The ‘tfind’ function is similar to the ‘tsearch’ function.  It
     locates an element matching the one pointed to by KEY and returns a
     pointer to this element.  But if no matching element is available
     no new element is entered (note that the ROOTP parameter points to
     a constant pointer).  Instead the function returns ‘NULL’.

   Another advantage of the ‘tsearch’ functions in contrast to the
‘hsearch’ functions is that there is an easy way to remove elements.

 -- Function: void * tdelete (const void *KEY, void **ROOTP,
          comparison_fn_t COMPAR)
     Preliminary: | MT-Safe race:rootp | AS-Unsafe heap | AC-Unsafe
     corrupt mem | *Note POSIX Safety Concepts::.

     To remove a specific element matching KEY from the tree ‘tdelete’
     can be used.  It locates the matching element using the same method
     as ‘tfind’.  The corresponding element is then removed and a
     pointer to the parent of the deleted node is returned by the
     function.  If there is no matching entry in the tree nothing can be
     deleted and the function returns ‘NULL’.  If the root of the tree
     is deleted ‘tdelete’ returns some unspecified value not equal to
     ‘NULL’.

 -- Function: void tdestroy (void *VROOT, __free_fn_t FREEFCT)
     Preliminary: | MT-Safe | AS-Unsafe heap | AC-Unsafe mem | *Note
     POSIX Safety Concepts::.

     If the complete search tree has to be removed one can use
     ‘tdestroy’.  It frees all resources allocated by the ‘tsearch’
     functions to generate the tree pointed to by VROOT.

     For the data in each tree node the function FREEFCT is called.  The
     pointer to the data is passed as the argument to the function.  If
     no such work is necessary FREEFCT must point to a function doing
     nothing.  It is called in any case.

     This function is a GNU extension and not covered by the System V or
     X/Open specifications.

   In addition to the functions to create and destroy the tree data
structure, there is another function which allows you to apply a
function to all elements of the tree.  The function must have this type:

     void __action_fn_t (const void *nodep, VISIT value, int level);

   The NODEP is the data value of the current node (once given as the
KEY argument to ‘tsearch’).  LEVEL is a numeric value which corresponds
to the depth of the current node in the tree.  The root node has the
depth 0 and its children have a depth of 1 and so on.  The ‘VISIT’ type
is an enumeration type.

 -- Data Type: VISIT
     The ‘VISIT’ value indicates the status of the current node in the
     tree and how the function is called.  The status of a node is
     either ‘leaf’ or ‘internal node’.  For each leaf node the function
     is called exactly once, for each internal node it is called three
     times: before the first child is processed, after the first child
     is processed and after both children are processed.  This makes it
     possible to handle all three methods of tree traversal (or even a
     combination of them).

     ‘preorder’
          The current node is an internal node and the function is
          called before the first child was processed.
     ‘postorder’
          The current node is an internal node and the function is
          called after the first child was processed.
     ‘endorder’
          The current node is an internal node and the function is
          called after the second child was processed.
     ‘leaf’
          The current node is a leaf.

 -- Function: void twalk (const void *ROOT, __action_fn_t ACTION)
     Preliminary: | MT-Safe race:root | AS-Safe | AC-Safe | *Note POSIX
     Safety Concepts::.

     For each node in the tree with a node pointed to by ROOT, the
     ‘twalk’ function calls the function provided by the parameter
     ACTION.  For leaf nodes the function is called exactly once with
     VALUE set to ‘leaf’.  For internal nodes the function is called
     three times, setting the VALUE parameter or ACTION to the
     appropriate value.  The LEVEL argument for the ACTION function is
     computed while descending the tree by increasing the value by one
     for each descent to a child, starting with the value 0 for the root
     node.

     Since the functions used for the ACTION parameter to ‘twalk’ must
     not modify the tree data, it is safe to run ‘twalk’ in more than
     one thread at the same time, working on the same tree.  It is also
     safe to call ‘tfind’ in parallel.  Functions which modify the tree
     must not be used, otherwise the behavior is undefined.


File: libc.info,  Node: Pattern Matching,  Next: I/O Overview,  Prev: Searching and Sorting,  Up: Top

10 Pattern Matching
*******************

The GNU C Library provides pattern matching facilities for two kinds of
patterns: regular expressions and file-name wildcards.  The library also
provides a facility for expanding variable and command references and
parsing text into words in the way the shell does.

* Menu:

* Wildcard Matching::    Matching a wildcard pattern against a single string.
* Globbing::             Finding the files that match a wildcard pattern.
* Regular Expressions::  Matching regular expressions against strings.
* Word Expansion::       Expanding shell variables, nested commands,
			    arithmetic, and wildcards.
			    This is what the shell does with shell commands.


File: libc.info,  Node: Wildcard Matching,  Next: Globbing,  Up: Pattern Matching

10.1 Wildcard Matching
======================

This section describes how to match a wildcard pattern against a
particular string.  The result is a yes or no answer: does the string
fit the pattern or not.  The symbols described here are all declared in
‘fnmatch.h’.

 -- Function: int fnmatch (const char *PATTERN, const char *STRING, int
          FLAGS)
     Preliminary: | MT-Safe env locale | AS-Unsafe heap | AC-Unsafe mem
     | *Note POSIX Safety Concepts::.

     This function tests whether the string STRING matches the pattern
     PATTERN.  It returns ‘0’ if they do match; otherwise, it returns
     the nonzero value ‘FNM_NOMATCH’.  The arguments PATTERN and STRING
     are both strings.

     The argument FLAGS is a combination of flag bits that alter the
     details of matching.  See below for a list of the defined flags.

     In the GNU C Library, ‘fnmatch’ might sometimes report “errors” by
     returning nonzero values that are not equal to ‘FNM_NOMATCH’.

   These are the available flags for the FLAGS argument:

‘FNM_FILE_NAME’
     Treat the ‘/’ character specially, for matching file names.  If
     this flag is set, wildcard constructs in PATTERN cannot match ‘/’
     in STRING.  Thus, the only way to match ‘/’ is with an explicit ‘/’
     in PATTERN.

‘FNM_PATHNAME’
     This is an alias for ‘FNM_FILE_NAME’; it comes from POSIX.2.  We
     don’t recommend this name because we don’t use the term “pathname”
     for file names.

‘FNM_PERIOD’
     Treat the ‘.’ character specially if it appears at the beginning of
     STRING.  If this flag is set, wildcard constructs in PATTERN cannot
     match ‘.’ as the first character of STRING.

     If you set both ‘FNM_PERIOD’ and ‘FNM_FILE_NAME’, then the special
     treatment applies to ‘.’ following ‘/’ as well as to ‘.’ at the
     beginning of STRING.  (The shell uses the ‘FNM_PERIOD’ and
     ‘FNM_FILE_NAME’ flags together for matching file names.)

‘FNM_NOESCAPE’
     Don’t treat the ‘\’ character specially in patterns.  Normally, ‘\’
     quotes the following character, turning off its special meaning (if
     any) so that it matches only itself.  When quoting is enabled, the
     pattern ‘\?’ matches only the string ‘?’, because the question mark
     in the pattern acts like an ordinary character.

     If you use ‘FNM_NOESCAPE’, then ‘\’ is an ordinary character.

‘FNM_LEADING_DIR’
     Ignore a trailing sequence of characters starting with a ‘/’ in
     STRING; that is to say, test whether STRING starts with a directory
     name that PATTERN matches.

     If this flag is set, either ‘foo*’ or ‘foobar’ as a pattern would
     match the string ‘foobar/frobozz’.

‘FNM_CASEFOLD’
     Ignore case in comparing STRING to PATTERN.

‘FNM_EXTMATCH’
     Besides the normal patterns, also recognize the extended patterns
     introduced in ‘ksh’.  The patterns are written in the form
     explained in the following table where PATTERN-LIST is a ‘|’
     separated list of patterns.

     ‘?(PATTERN-LIST)’
          The pattern matches if zero or one occurrences of any of the
          patterns in the PATTERN-LIST allow matching the input string.

     ‘*(PATTERN-LIST)’
          The pattern matches if zero or more occurrences of any of the
          patterns in the PATTERN-LIST allow matching the input string.

     ‘+(PATTERN-LIST)’
          The pattern matches if one or more occurrences of any of the
          patterns in the PATTERN-LIST allow matching the input string.

     ‘@(PATTERN-LIST)’
          The pattern matches if exactly one occurrence of any of the
          patterns in the PATTERN-LIST allows matching the input string.

     ‘!(PATTERN-LIST)’
          The pattern matches if the input string cannot be matched with
          any of the patterns in the PATTERN-LIST.


File: libc.info,  Node: Globbing,  Next: Regular Expressions,  Prev: Wildcard Matching,  Up: Pattern Matching

10.2 Globbing
=============

The archetypal use of wildcards is for matching against the files in a
directory, and making a list of all the matches.  This is called
"globbing".

   You could do this using ‘fnmatch’, by reading the directory entries
one by one and testing each one with ‘fnmatch’.  But that would be slow
(and complex, since you would have to handle subdirectories by hand).

   The library provides a function ‘glob’ to make this particular use of
wildcards convenient.  ‘glob’ and the other symbols in this section are
declared in ‘glob.h’.

* Menu:

* Calling Glob::             Basic use of ‘glob’.
* Flags for Globbing::       Flags that enable various options in ‘glob’.
* More Flags for Globbing::  GNU specific extensions to ‘glob’.


File: libc.info,  Node: Calling Glob,  Next: Flags for Globbing,  Up: Globbing

10.2.1 Calling ‘glob’
---------------------

The result of globbing is a vector of file names (strings).  To return
this vector, ‘glob’ uses a special data type, ‘glob_t’, which is a
structure.  You pass ‘glob’ the address of the structure, and it fills
in the structure’s fields to tell you about the results.

 -- Data Type: glob_t
     This data type holds a pointer to a word vector.  More precisely,
     it records both the address of the word vector and its size.  The
     GNU implementation contains some more fields which are non-standard
     extensions.

     ‘gl_pathc’
          The number of elements in the vector, excluding the initial
          null entries if the GLOB_DOOFFS flag is used (see gl_offs
          below).

     ‘gl_pathv’
          The address of the vector.  This field has type ‘char **’.

     ‘gl_offs’
          The offset of the first real element of the vector, from its
          nominal address in the ‘gl_pathv’ field.  Unlike the other
          fields, this is always an input to ‘glob’, rather than an
          output from it.

          If you use a nonzero offset, then that many elements at the
          beginning of the vector are left empty.  (The ‘glob’ function
          fills them with null pointers.)

          The ‘gl_offs’ field is meaningful only if you use the
          ‘GLOB_DOOFFS’ flag.  Otherwise, the offset is always zero
          regardless of what is in this field, and the first real
          element comes at the beginning of the vector.

     ‘gl_closedir’
          The address of an alternative implementation of the ‘closedir’
          function.  It is used if the ‘GLOB_ALTDIRFUNC’ bit is set in
          the flag parameter.  The type of this field is
          ‘void (*) (void *)’.

          This is a GNU extension.

     ‘gl_readdir’
          The address of an alternative implementation of the ‘readdir’
          function used to read the contents of a directory.  It is used
          if the ‘GLOB_ALTDIRFUNC’ bit is set in the flag parameter.
          The type of this field is ‘struct dirent *(*) (void *)’.

          An implementation of ‘gl_readdir’ needs to initialize the
          following members of the ‘struct dirent’ object:

          ‘d_type’
               This member should be set to the file type of the entry
               if it is known.  Otherwise, the value ‘DT_UNKNOWN’ can be
               used.  The ‘glob’ function may use the specified file
               type to avoid callbacks in cases where the file type
               indicates that the data is not required.

          ‘d_ino’
               This member needs to be non-zero, otherwise ‘glob’ may
               skip the current entry and call the ‘gl_readdir’ callback
               function again to retrieve another entry.

          ‘d_name’
               This member must be set to the name of the entry.  It
               must be null-terminated.

          The example below shows how to allocate a ‘struct dirent’
          object containing a given name.


               #include <dirent.h>
               #include <errno.h>
               #include <stddef.h>
               #include <stdlib.h>
               #include <string.h>

               struct dirent *
               mkdirent (const char *name)
               {
                 size_t dirent_size = offsetof (struct dirent, d_name) + 1;
                 size_t name_length = strlen (name);
                 size_t total_size = dirent_size + name_length;
                 if (total_size < dirent_size)
                   {
                     errno = ENOMEM;
                     return NULL;
                   }
                 struct dirent *result = malloc (total_size);
                 if (result == NULL)
                   return NULL;
                 result->d_type = DT_UNKNOWN;
                 result->d_ino = 1;            /* Do not skip this entry. */
                 memcpy (result->d_name, name, name_length + 1);
                 return result;
               }

          The ‘glob’ function reads the ‘struct dirent’ members listed
          above and makes a copy of the file name in the ‘d_name’ member
          immediately after the ‘gl_readdir’ callback function returns.
          Future invocations of any of the callback functions may
          dealloacte or reuse the buffer.  It is the responsibility of
          the caller of the ‘glob’ function to allocate and deallocate
          the buffer, around the call to ‘glob’ or using the callback
          functions.  For example, an application could allocate the
          buffer in the ‘gl_readdir’ callback function, and deallocate
          it in the ‘gl_closedir’ callback function.

          The ‘gl_readdir’ member is a GNU extension.

     ‘gl_opendir’
          The address of an alternative implementation of the ‘opendir’
          function.  It is used if the ‘GLOB_ALTDIRFUNC’ bit is set in
          the flag parameter.  The type of this field is
          ‘void *(*) (const char *)’.

          This is a GNU extension.

     ‘gl_stat’
          The address of an alternative implementation of the ‘stat’
          function to get information about an object in the filesystem.
          It is used if the ‘GLOB_ALTDIRFUNC’ bit is set in the flag
          parameter.  The type of this field is
          ‘int (*) (const char *, struct stat *)’.

          This is a GNU extension.

     ‘gl_lstat’
          The address of an alternative implementation of the ‘lstat’
          function to get information about an object in the
          filesystems, not following symbolic links.  It is used if the
          ‘GLOB_ALTDIRFUNC’ bit is set in the flag parameter.  The type
          of this field is ‘int (*) (const char *, struct stat *)’.

          This is a GNU extension.

     ‘gl_flags’
          The flags used when ‘glob’ was called.  In addition,
          ‘GLOB_MAGCHAR’ might be set.  See *note Flags for Globbing::
          for more details.

          This is a GNU extension.

   For use in the ‘glob64’ function ‘glob.h’ contains another definition
for a very similar type.  ‘glob64_t’ differs from ‘glob_t’ only in the
types of the members ‘gl_readdir’, ‘gl_stat’, and ‘gl_lstat’.

 -- Data Type: glob64_t
     This data type holds a pointer to a word vector.  More precisely,
     it records both the address of the word vector and its size.  The
     GNU implementation contains some more fields which are non-standard
     extensions.

     ‘gl_pathc’
          The number of elements in the vector, excluding the initial
          null entries if the GLOB_DOOFFS flag is used (see gl_offs
          below).

     ‘gl_pathv’
          The address of the vector.  This field has type ‘char **’.

     ‘gl_offs’
          The offset of the first real element of the vector, from its
          nominal address in the ‘gl_pathv’ field.  Unlike the other
          fields, this is always an input to ‘glob’, rather than an
          output from it.

          If you use a nonzero offset, then that many elements at the
          beginning of the vector are left empty.  (The ‘glob’ function
          fills them with null pointers.)

          The ‘gl_offs’ field is meaningful only if you use the
          ‘GLOB_DOOFFS’ flag.  Otherwise, the offset is always zero
          regardless of what is in this field, and the first real
          element comes at the beginning of the vector.

     ‘gl_closedir’
          The address of an alternative implementation of the ‘closedir’
          function.  It is used if the ‘GLOB_ALTDIRFUNC’ bit is set in
          the flag parameter.  The type of this field is
          ‘void (*) (void *)’.

          This is a GNU extension.

     ‘gl_readdir’
          The address of an alternative implementation of the
          ‘readdir64’ function used to read the contents of a directory.
          It is used if the ‘GLOB_ALTDIRFUNC’ bit is set in the flag
          parameter.  The type of this field is
          ‘struct dirent64 *(*) (void *)’.

          This is a GNU extension.

     ‘gl_opendir’
          The address of an alternative implementation of the ‘opendir’
          function.  It is used if the ‘GLOB_ALTDIRFUNC’ bit is set in
          the flag parameter.  The type of this field is
          ‘void *(*) (const char *)’.

          This is a GNU extension.

     ‘gl_stat’
          The address of an alternative implementation of the ‘stat64’
          function to get information about an object in the filesystem.
          It is used if the ‘GLOB_ALTDIRFUNC’ bit is set in the flag
          parameter.  The type of this field is
          ‘int (*) (const char *, struct stat64 *)’.

          This is a GNU extension.

     ‘gl_lstat’
          The address of an alternative implementation of the ‘lstat64’
          function to get information about an object in the
          filesystems, not following symbolic links.  It is used if the
          ‘GLOB_ALTDIRFUNC’ bit is set in the flag parameter.  The type
          of this field is ‘int (*) (const char *, struct stat64 *)’.

          This is a GNU extension.

     ‘gl_flags’
          The flags used when ‘glob’ was called.  In addition,
          ‘GLOB_MAGCHAR’ might be set.  See *note Flags for Globbing::
          for more details.

          This is a GNU extension.

 -- Function: int glob (const char *PATTERN, int FLAGS, int (*ERRFUNC)
          (const char *FILENAME, int ERROR-CODE), glob_t *VECTOR-PTR)
     Preliminary: | MT-Unsafe race:utent env sig:ALRM timer locale |
     AS-Unsafe dlopen plugin corrupt heap lock | AC-Unsafe corrupt lock
     fd mem | *Note POSIX Safety Concepts::.

     The function ‘glob’ does globbing using the pattern PATTERN in the
     current directory.  It puts the result in a newly allocated vector,
     and stores the size and address of this vector into ‘*VECTOR-PTR’.
     The argument FLAGS is a combination of bit flags; see *note Flags
     for Globbing::, for details of the flags.

     The result of globbing is a sequence of file names.  The function
     ‘glob’ allocates a string for each resulting word, then allocates a
     vector of type ‘char **’ to store the addresses of these strings.
     The last element of the vector is a null pointer.  This vector is
     called the "word vector".

     To return this vector, ‘glob’ stores both its address and its
     length (number of elements, not counting the terminating null
     pointer) into ‘*VECTOR-PTR’.

     Normally, ‘glob’ sorts the file names alphabetically before
     returning them.  You can turn this off with the flag ‘GLOB_NOSORT’
     if you want to get the information as fast as possible.  Usually
     it’s a good idea to let ‘glob’ sort them—if you process the files
     in alphabetical order, the users will have a feel for the rate of
     progress that your application is making.

     If ‘glob’ succeeds, it returns 0.  Otherwise, it returns one of
     these error codes:

     ‘GLOB_ABORTED’
          There was an error opening a directory, and you used the flag
          ‘GLOB_ERR’ or your specified ERRFUNC returned a nonzero value.
          *Note Flags for Globbing::, for an explanation of the
          ‘GLOB_ERR’ flag and ERRFUNC.

     ‘GLOB_NOMATCH’
          The pattern didn’t match any existing files.  If you use the
          ‘GLOB_NOCHECK’ flag, then you never get this error code,
          because that flag tells ‘glob’ to _pretend_ that the pattern
          matched at least one file.

     ‘GLOB_NOSPACE’
          It was impossible to allocate memory to hold the result.

     In the event of an error, ‘glob’ stores information in
     ‘*VECTOR-PTR’ about all the matches it has found so far.

     It is important to notice that the ‘glob’ function will not fail if
     it encounters directories or files which cannot be handled without
     the LFS interfaces.  The implementation of ‘glob’ is supposed to
     use these functions internally.  This at least is the assumption
     made by the Unix standard.  The GNU extension of allowing the user
     to provide their own directory handling and ‘stat’ functions
     complicates things a bit.  If these callback functions are used and
     a large file or directory is encountered ‘glob’ _can_ fail.

 -- Function: int glob64 (const char *PATTERN, int FLAGS, int (*ERRFUNC)
          (const char *FILENAME, int ERROR-CODE), glob64_t *VECTOR-PTR)
     Preliminary: | MT-Unsafe race:utent env sig:ALRM timer locale |
     AS-Unsafe dlopen corrupt heap lock | AC-Unsafe corrupt lock fd mem
     | *Note POSIX Safety Concepts::.

     The ‘glob64’ function was added as part of the Large File Summit
     extensions but is not part of the original LFS proposal.  The
     reason for this is simple: it is not necessary.  The necessity for
     a ‘glob64’ function is added by the extensions of the GNU ‘glob’
     implementation which allows the user to provide their own directory
     handling and ‘stat’ functions.  The ‘readdir’ and ‘stat’ functions
     do depend on the choice of ‘_FILE_OFFSET_BITS’ since the definition
     of the types ‘struct dirent’ and ‘struct stat’ will change
     depending on the choice.

     Besides this difference, ‘glob64’ works just like ‘glob’ in all
     aspects.

     This function is a GNU extension.


File: libc.info,  Node: Flags for Globbing,  Next: More Flags for Globbing,  Prev: Calling Glob,  Up: Globbing

10.2.2 Flags for Globbing
-------------------------

This section describes the standard flags that you can specify in the
FLAGS argument to ‘glob’.  Choose the flags you want, and combine them
with the C bitwise OR operator ‘|’.

   Note that there are *note More Flags for Globbing:: available as GNU
extensions.

‘GLOB_APPEND’
     Append the words from this expansion to the vector of words
     produced by previous calls to ‘glob’.  This way you can effectively
     expand several words as if they were concatenated with spaces
     between them.

     In order for appending to work, you must not modify the contents of
     the word vector structure between calls to ‘glob’.  And, if you set
     ‘GLOB_DOOFFS’ in the first call to ‘glob’, you must also set it
     when you append to the results.

     Note that the pointer stored in ‘gl_pathv’ may no longer be valid
     after you call ‘glob’ the second time, because ‘glob’ might have
     relocated the vector.  So always fetch ‘gl_pathv’ from the ‘glob_t’
     structure after each ‘glob’ call; *never* save the pointer across
     calls.

‘GLOB_DOOFFS’
     Leave blank slots at the beginning of the vector of words.  The
     ‘gl_offs’ field says how many slots to leave.  The blank slots
     contain null pointers.

‘GLOB_ERR’
     Give up right away and report an error if there is any difficulty
     reading the directories that must be read in order to expand
     PATTERN fully.  Such difficulties might include a directory in
     which you don’t have the requisite access.  Normally, ‘glob’ tries
     its best to keep on going despite any errors, reading whatever
     directories it can.

     You can exercise even more control than this by specifying an
     error-handler function ERRFUNC when you call ‘glob’.  If ERRFUNC is
     not a null pointer, then ‘glob’ doesn’t give up right away when it
     can’t read a directory; instead, it calls ERRFUNC with two
     arguments, like this:

          (*ERRFUNC) (FILENAME, ERROR-CODE)

     The argument FILENAME is the name of the directory that ‘glob’
     couldn’t open or couldn’t read, and ERROR-CODE is the ‘errno’ value
     that was reported to ‘glob’.

     If the error handler function returns nonzero, then ‘glob’ gives up
     right away.  Otherwise, it continues.

‘GLOB_MARK’
     If the pattern matches the name of a directory, append ‘/’ to the
     directory’s name when returning it.

‘GLOB_NOCHECK’
     If the pattern doesn’t match any file names, return the pattern
     itself as if it were a file name that had been matched.  (Normally,
     when the pattern doesn’t match anything, ‘glob’ returns that there
     were no matches.)

‘GLOB_NOESCAPE’
     Don’t treat the ‘\’ character specially in patterns.  Normally, ‘\’
     quotes the following character, turning off its special meaning (if
     any) so that it matches only itself.  When quoting is enabled, the
     pattern ‘\?’ matches only the string ‘?’, because the question mark
     in the pattern acts like an ordinary character.

     If you use ‘GLOB_NOESCAPE’, then ‘\’ is an ordinary character.

     ‘glob’ does its work by calling the function ‘fnmatch’ repeatedly.
     It handles the flag ‘GLOB_NOESCAPE’ by turning on the
     ‘FNM_NOESCAPE’ flag in calls to ‘fnmatch’.

‘GLOB_NOSORT’
     Don’t sort the file names; return them in no particular order.  (In
     practice, the order will depend on the order of the entries in the
     directory.)  The only reason _not_ to sort is to save time.


File: libc.info,  Node: More Flags for Globbing,  Prev: Flags for Globbing,  Up: Globbing

10.2.3 More Flags for Globbing
------------------------------

Beside the flags described in the last section, the GNU implementation
of ‘glob’ allows a few more flags which are also defined in the ‘glob.h’
file.  Some of the extensions implement functionality which is available
in modern shell implementations.

‘GLOB_PERIOD’
     The ‘.’ character (period) is treated special.  It cannot be
     matched by wildcards.  *Note Wildcard Matching::, ‘FNM_PERIOD’.

‘GLOB_MAGCHAR’
     The ‘GLOB_MAGCHAR’ value is not to be given to ‘glob’ in the FLAGS
     parameter.  Instead, ‘glob’ sets this bit in the GL_FLAGS element
     of the GLOB_T structure provided as the result if the pattern used
     for matching contains any wildcard character.

‘GLOB_ALTDIRFUNC’
     Instead of using the normal functions for accessing the filesystem
     the ‘glob’ implementation uses the user-supplied functions
     specified in the structure pointed to by PGLOB parameter.  For more
     information about the functions refer to the sections about
     directory handling see *note Accessing Directories::, and *note
     Reading Attributes::.

‘GLOB_BRACE’
     If this flag is given, the handling of braces in the pattern is
     changed.  It is now required that braces appear correctly grouped.
     I.e., for each opening brace there must be a closing one.  Braces
     can be used recursively.  So it is possible to define one brace
     expression in another one.  It is important to note that the range
     of each brace expression is completely contained in the outer brace
     expression (if there is one).

     The string between the matching braces is separated into single
     expressions by splitting at ‘,’ (comma) characters.  The commas
     themselves are discarded.  Please note what we said above about
     recursive brace expressions.  The commas used to separate the
     subexpressions must be at the same level.  Commas in brace
     subexpressions are not matched.  They are used during expansion of
     the brace expression of the deeper level.  The example below shows
     this

          glob ("{foo/{,bar,biz},baz}", GLOB_BRACE, NULL, &result)

     is equivalent to the sequence

          glob ("foo/", GLOB_BRACE, NULL, &result)
          glob ("foo/bar", GLOB_BRACE|GLOB_APPEND, NULL, &result)
          glob ("foo/biz", GLOB_BRACE|GLOB_APPEND, NULL, &result)
          glob ("baz", GLOB_BRACE|GLOB_APPEND, NULL, &result)

     if we leave aside error handling.

‘GLOB_NOMAGIC’
     If the pattern contains no wildcard constructs (it is a literal
     file name), return it as the sole “matching” word, even if no file
     exists by that name.

‘GLOB_TILDE’
     If this flag is used the character ‘~’ (tilde) is handled specially
     if it appears at the beginning of the pattern.  Instead of being
     taken verbatim it is used to represent the home directory of a
     known user.

     If ‘~’ is the only character in pattern or it is followed by a ‘/’
     (slash), the home directory of the process owner is substituted.
     Using ‘getlogin’ and ‘getpwnam’ the information is read from the
     system databases.  As an example take user ‘bart’ with his home
     directory at ‘/home/bart’.  For him a call like

          glob ("~/bin/*", GLOB_TILDE, NULL, &result)

     would return the contents of the directory ‘/home/bart/bin’.
     Instead of referring to the own home directory it is also possible
     to name the home directory of other users.  To do so one has to
     append the user name after the tilde character.  So the contents of
     user ‘homer’’s ‘bin’ directory can be retrieved by

          glob ("~homer/bin/*", GLOB_TILDE, NULL, &result)

     If the user name is not valid or the home directory cannot be
     determined for some reason the pattern is left untouched and itself
     used as the result.  I.e., if in the last example ‘home’ is not
     available the tilde expansion yields to ‘"~homer/bin/*"’ and ‘glob’
     is not looking for a directory named ‘~homer’.

     This functionality is equivalent to what is available in C-shells
     if the ‘nonomatch’ flag is set.

‘GLOB_TILDE_CHECK’
     If this flag is used ‘glob’ behaves as if ‘GLOB_TILDE’ is given.
     The only difference is that if the user name is not available or
     the home directory cannot be determined for other reasons this
     leads to an error.  ‘glob’ will return ‘GLOB_NOMATCH’ instead of
     using the pattern itself as the name.

     This functionality is equivalent to what is available in C-shells
     if the ‘nonomatch’ flag is not set.

‘GLOB_ONLYDIR’
     If this flag is used the globbing function takes this as a *hint*
     that the caller is only interested in directories matching the
     pattern.  If the information about the type of the file is easily
     available non-directories will be rejected but no extra work will
     be done to determine the information for each file.  I.e., the
     caller must still be able to filter directories out.

     This functionality is only available with the GNU ‘glob’
     implementation.  It is mainly used internally to increase the
     performance but might be useful for a user as well and therefore is
     documented here.

   Calling ‘glob’ will in most cases allocate resources which are used
to represent the result of the function call.  If the same object of
type ‘glob_t’ is used in multiple call to ‘glob’ the resources are freed
or reused so that no leaks appear.  But this does not include the time
when all ‘glob’ calls are done.

 -- Function: void globfree (glob_t *PGLOB)
     Preliminary: | MT-Safe | AS-Unsafe corrupt heap | AC-Unsafe corrupt
     mem | *Note POSIX Safety Concepts::.

     The ‘globfree’ function frees all resources allocated by previous
     calls to ‘glob’ associated with the object pointed to by PGLOB.
     This function should be called whenever the currently used ‘glob_t’
     typed object isn’t used anymore.

 -- Function: void globfree64 (glob64_t *PGLOB)
     Preliminary: | MT-Safe | AS-Unsafe corrupt lock | AC-Unsafe corrupt
     lock fd mem | *Note POSIX Safety Concepts::.

     This function is equivalent to ‘globfree’ but it frees records of
     type ‘glob64_t’ which were allocated by ‘glob64’.


File: libc.info,  Node: Regular Expressions,  Next: Word Expansion,  Prev: Globbing,  Up: Pattern Matching

10.3 Regular Expression Matching
================================

The GNU C Library supports two interfaces for matching regular
expressions.  One is the standard POSIX.2 interface, and the other is
what the GNU C Library has had for many years.

   Both interfaces are declared in the header file ‘regex.h’.  If you
define ‘_POSIX_C_SOURCE’, then only the POSIX.2 functions, structures,
and constants are declared.

* Menu:

* POSIX Regexp Compilation::    Using ‘regcomp’ to prepare to match.
* Flags for POSIX Regexps::     Syntax variations for ‘regcomp’.
* Matching POSIX Regexps::      Using ‘regexec’ to match the compiled
				   pattern that you get from ‘regcomp’.
* Regexp Subexpressions::       Finding which parts of the string were matched.
* Subexpression Complications:: Find points of which parts were matched.
* Regexp Cleanup::		Freeing storage; reporting errors.


File: libc.info,  Node: POSIX Regexp Compilation,  Next: Flags for POSIX Regexps,  Up: Regular Expressions

10.3.1 POSIX Regular Expression Compilation
-------------------------------------------

Before you can actually match a regular expression, you must "compile"
it.  This is not true compilation—it produces a special data structure,
not machine instructions.  But it is like ordinary compilation in that
its purpose is to enable you to “execute” the pattern fast.  (*Note
Matching POSIX Regexps::, for how to use the compiled regular expression
for matching.)

   There is a special data type for compiled regular expressions:

 -- Data Type: regex_t
     This type of object holds a compiled regular expression.  It is
     actually a structure.  It has just one field that your programs
     should look at:

     ‘re_nsub’
          This field holds the number of parenthetical subexpressions in
          the regular expression that was compiled.

     There are several other fields, but we don’t describe them here,
     because only the functions in the library should use them.

   After you create a ‘regex_t’ object, you can compile a regular
expression into it by calling ‘regcomp’.

 -- Function: int regcomp (regex_t *restrict COMPILED, const char
          *restrict PATTERN, int CFLAGS)
     Preliminary: | MT-Safe locale | AS-Unsafe corrupt heap lock dlopen
     | AC-Unsafe corrupt lock mem fd | *Note POSIX Safety Concepts::.

     The function ‘regcomp’ “compiles” a regular expression into a data
     structure that you can use with ‘regexec’ to match against a
     string.  The compiled regular expression format is designed for
     efficient matching.  ‘regcomp’ stores it into ‘*COMPILED’.

     It’s up to you to allocate an object of type ‘regex_t’ and pass its
     address to ‘regcomp’.

     The argument CFLAGS lets you specify various options that control
     the syntax and semantics of regular expressions.  *Note Flags for
     POSIX Regexps::.

     If you use the flag ‘REG_NOSUB’, then ‘regcomp’ omits from the
     compiled regular expression the information necessary to record how
     subexpressions actually match.  In this case, you might as well
     pass ‘0’ for the MATCHPTR and NMATCH arguments when you call
     ‘regexec’.

     If you don’t use ‘REG_NOSUB’, then the compiled regular expression
     does have the capacity to record how subexpressions match.  Also,
     ‘regcomp’ tells you how many subexpressions PATTERN has, by storing
     the number in ‘COMPILED->re_nsub’.  You can use that value to
     decide how long an array to allocate to hold information about
     subexpression matches.

     ‘regcomp’ returns ‘0’ if it succeeds in compiling the regular
     expression; otherwise, it returns a nonzero error code (see the
     table below).  You can use ‘regerror’ to produce an error message
     string describing the reason for a nonzero value; see *note Regexp
     Cleanup::.

   Here are the possible nonzero values that ‘regcomp’ can return:

‘REG_BADBR’
     There was an invalid ‘\{…\}’ construct in the regular expression.
     A valid ‘\{…\}’ construct must contain either a single number, or
     two numbers in increasing order separated by a comma.

‘REG_BADPAT’
     There was a syntax error in the regular expression.

‘REG_BADRPT’
     A repetition operator such as ‘?’ or ‘*’ appeared in a bad position
     (with no preceding subexpression to act on).

‘REG_ECOLLATE’
     The regular expression referred to an invalid collating element
     (one not defined in the current locale for string collation).
     *Note Locale Categories::.

‘REG_ECTYPE’
     The regular expression referred to an invalid character class name.

‘REG_EESCAPE’
     The regular expression ended with ‘\’.

‘REG_ESUBREG’
     There was an invalid number in the ‘\DIGIT’ construct.

‘REG_EBRACK’
     There were unbalanced square brackets in the regular expression.

‘REG_EPAREN’
     An extended regular expression had unbalanced parentheses, or a
     basic regular expression had unbalanced ‘\(’ and ‘\)’.

‘REG_EBRACE’
     The regular expression had unbalanced ‘\{’ and ‘\}’.

‘REG_ERANGE’
     One of the endpoints in a range expression was invalid.

‘REG_ESPACE’
     ‘regcomp’ ran out of memory.


File: libc.info,  Node: Flags for POSIX Regexps,  Next: Matching POSIX Regexps,  Prev: POSIX Regexp Compilation,  Up: Regular Expressions

10.3.2 Flags for POSIX Regular Expressions
------------------------------------------

These are the bit flags that you can use in the CFLAGS operand when
compiling a regular expression with ‘regcomp’.

‘REG_EXTENDED’
     Treat the pattern as an extended regular expression, rather than as
     a basic regular expression.

‘REG_ICASE’
     Ignore case when matching letters.

‘REG_NOSUB’
     Don’t bother storing the contents of the MATCHPTR array.

‘REG_NEWLINE’
     Treat a newline in STRING as dividing STRING into multiple lines,
     so that ‘$’ can match before the newline and ‘^’ can match after.
     Also, don’t permit ‘.’ to match a newline, and don’t permit ‘[^…]’
     to match a newline.

     Otherwise, newline acts like any other ordinary character.


File: libc.info,  Node: Matching POSIX Regexps,  Next: Regexp Subexpressions,  Prev: Flags for POSIX Regexps,  Up: Regular Expressions

10.3.3 Matching a Compiled POSIX Regular Expression
---------------------------------------------------

Once you have compiled a regular expression, as described in *note POSIX
Regexp Compilation::, you can match it against strings using ‘regexec’.
A match anywhere inside the string counts as success, unless the regular
expression contains anchor characters (‘^’ or ‘$’).

 -- Function: int regexec (const regex_t *restrict COMPILED, const char
          *restrict STRING, size_t NMATCH, regmatch_t
          MATCHPTR[restrict], int EFLAGS)
     Preliminary: | MT-Safe locale | AS-Unsafe corrupt heap lock dlopen
     | AC-Unsafe corrupt lock mem fd | *Note POSIX Safety Concepts::.

     This function tries to match the compiled regular expression
     ‘*COMPILED’ against STRING.

     ‘regexec’ returns ‘0’ if the regular expression matches; otherwise,
     it returns a nonzero value.  See the table below for what nonzero
     values mean.  You can use ‘regerror’ to produce an error message
     string describing the reason for a nonzero value; see *note Regexp
     Cleanup::.

     The argument EFLAGS is a word of bit flags that enable various
     options.

     If you want to get information about what part of STRING actually
     matched the regular expression or its subexpressions, use the
     arguments MATCHPTR and NMATCH.  Otherwise, pass ‘0’ for NMATCH, and
     ‘NULL’ for MATCHPTR.  *Note Regexp Subexpressions::.

   You must match the regular expression with the same set of current
locales that were in effect when you compiled the regular expression.

   The function ‘regexec’ accepts the following flags in the EFLAGS
argument:

‘REG_NOTBOL’
     Do not regard the beginning of the specified string as the
     beginning of a line; more generally, don’t make any assumptions
     about what text might precede it.

‘REG_NOTEOL’
     Do not regard the end of the specified string as the end of a line;
     more generally, don’t make any assumptions about what text might
     follow it.

   Here are the possible nonzero values that ‘regexec’ can return:

‘REG_NOMATCH’
     The pattern didn’t match the string.  This isn’t really an error.

‘REG_ESPACE’
     ‘regexec’ ran out of memory.


File: libc.info,  Node: Regexp Subexpressions,  Next: Subexpression Complications,  Prev: Matching POSIX Regexps,  Up: Regular Expressions

10.3.4 Match Results with Subexpressions
----------------------------------------

When ‘regexec’ matches parenthetical subexpressions of PATTERN, it
records which parts of STRING they match.  It returns that information
by storing the offsets into an array whose elements are structures of
type ‘regmatch_t’.  The first element of the array (index ‘0’) records
the part of the string that matched the entire regular expression.  Each
other element of the array records the beginning and end of the part
that matched a single parenthetical subexpression.

 -- Data Type: regmatch_t
     This is the data type of the MATCHPTR array that you pass to
     ‘regexec’.  It contains two structure fields, as follows:

     ‘rm_so’
          The offset in STRING of the beginning of a substring.  Add
          this value to STRING to get the address of that part.

     ‘rm_eo’
          The offset in STRING of the end of the substring.

 -- Data Type: regoff_t
     ‘regoff_t’ is an alias for another signed integer type.  The fields
     of ‘regmatch_t’ have type ‘regoff_t’.

   The ‘regmatch_t’ elements correspond to subexpressions positionally;
the first element (index ‘1’) records where the first subexpression
matched, the second element records the second subexpression, and so on.
The order of the subexpressions is the order in which they begin.

   When you call ‘regexec’, you specify how long the MATCHPTR array is,
with the NMATCH argument.  This tells ‘regexec’ how many elements to
store.  If the actual regular expression has more than NMATCH
subexpressions, then you won’t get offset information about the rest of
them.  But this doesn’t alter whether the pattern matches a particular
string or not.

   If you don’t want ‘regexec’ to return any information about where the
subexpressions matched, you can either supply ‘0’ for NMATCH, or use the
flag ‘REG_NOSUB’ when you compile the pattern with ‘regcomp’.


File: libc.info,  Node: Subexpression Complications,  Next: Regexp Cleanup,  Prev: Regexp Subexpressions,  Up: Regular Expressions

10.3.5 Complications in Subexpression Matching
----------------------------------------------

Sometimes a subexpression matches a substring of no characters.  This
happens when ‘f\(o*\)’ matches the string ‘fum’.  (It really matches
just the ‘f’.)  In this case, both of the offsets identify the point in
the string where the null substring was found.  In this example, the
offsets are both ‘1’.

   Sometimes the entire regular expression can match without using some
of its subexpressions at all—for example, when ‘ba\(na\)*’ matches the
string ‘ba’, the parenthetical subexpression is not used.  When this
happens, ‘regexec’ stores ‘-1’ in both fields of the element for that
subexpression.

   Sometimes matching the entire regular expression can match a
particular subexpression more than once—for example, when ‘ba\(na\)*’
matches the string ‘bananana’, the parenthetical subexpression matches
three times.  When this happens, ‘regexec’ usually stores the offsets of
the last part of the string that matched the subexpression.  In the case
of ‘bananana’, these offsets are ‘6’ and ‘8’.

   But the last match is not always the one that is chosen.  It’s more
accurate to say that the last _opportunity_ to match is the one that
takes precedence.  What this means is that when one subexpression
appears within another, then the results reported for the inner
subexpression reflect whatever happened on the last match of the outer
subexpression.  For an example, consider ‘\(ba\(na\)*s \)*’ matching the
string ‘bananas bas ’.  The last time the inner expression actually
matches is near the end of the first word.  But it is _considered_ again
in the second word, and fails to match there.  ‘regexec’ reports nonuse
of the “na” subexpression.

   Another place where this rule applies is when the regular expression
     \(ba\(na\)*s \|nefer\(ti\)* \)*
matches ‘bananas nefertiti’.  The “na” subexpression does match in the
first word, but it doesn’t match in the second word because the other
alternative is used there.  Once again, the second repetition of the
outer subexpression overrides the first, and within that second
repetition, the “na” subexpression is not used.  So ‘regexec’ reports
nonuse of the “na” subexpression.


File: libc.info,  Node: Regexp Cleanup,  Prev: Subexpression Complications,  Up: Regular Expressions

10.3.6 POSIX Regexp Matching Cleanup
------------------------------------

When you are finished using a compiled regular expression, you can free
the storage it uses by calling ‘regfree’.

 -- Function: void regfree (regex_t *COMPILED)
     Preliminary: | MT-Safe | AS-Unsafe heap | AC-Unsafe mem | *Note
     POSIX Safety Concepts::.

     Calling ‘regfree’ frees all the storage that ‘*COMPILED’ points to.
     This includes various internal fields of the ‘regex_t’ structure
     that aren’t documented in this manual.

     ‘regfree’ does not free the object ‘*COMPILED’ itself.

   You should always free the space in a ‘regex_t’ structure with
‘regfree’ before using the structure to compile another regular
expression.

   When ‘regcomp’ or ‘regexec’ reports an error, you can use the
function ‘regerror’ to turn it into an error message string.

 -- Function: size_t regerror (int ERRCODE, const regex_t *restrict
          COMPILED, char *restrict BUFFER, size_t LENGTH)
     Preliminary: | MT-Safe env | AS-Unsafe corrupt heap lock dlopen |
     AC-Unsafe corrupt lock fd mem | *Note POSIX Safety Concepts::.

     This function produces an error message string for the error code
     ERRCODE, and stores the string in LENGTH bytes of memory starting
     at BUFFER.  For the COMPILED argument, supply the same compiled
     regular expression structure that ‘regcomp’ or ‘regexec’ was
     working with when it got the error.  Alternatively, you can supply
     ‘NULL’ for COMPILED; you will still get a meaningful error message,
     but it might not be as detailed.

     If the error message can’t fit in LENGTH bytes (including a
     terminating null character), then ‘regerror’ truncates it.  The
     string that ‘regerror’ stores is always null-terminated even if it
     has been truncated.

     The return value of ‘regerror’ is the minimum length needed to
     store the entire error message.  If this is less than LENGTH, then
     the error message was not truncated, and you can use it.
     Otherwise, you should call ‘regerror’ again with a larger buffer.

     Here is a function which uses ‘regerror’, but always dynamically
     allocates a buffer for the error message:

          char *get_regerror (int errcode, regex_t *compiled)
          {
            size_t length = regerror (errcode, compiled, NULL, 0);
            char *buffer = xmalloc (length);
            (void) regerror (errcode, compiled, buffer, length);
            return buffer;
          }


File: libc.info,  Node: Word Expansion,  Prev: Regular Expressions,  Up: Pattern Matching

10.4 Shell-Style Word Expansion
===============================

"Word expansion" means the process of splitting a string into "words"
and substituting for variables, commands, and wildcards just as the
shell does.

   For example, when you write ‘ls -l foo.c’, this string is split into
three separate words—‘ls’, ‘-l’ and ‘foo.c’.  This is the most basic
function of word expansion.

   When you write ‘ls *.c’, this can become many words, because the word
‘*.c’ can be replaced with any number of file names.  This is called
"wildcard expansion", and it is also a part of word expansion.

   When you use ‘echo $PATH’ to print your path, you are taking
advantage of "variable substitution", which is also part of word
expansion.

   Ordinary programs can perform word expansion just like the shell by
calling the library function ‘wordexp’.

* Menu:

* Expansion Stages::            What word expansion does to a string.
* Calling Wordexp::             How to call ‘wordexp’.
* Flags for Wordexp::           Options you can enable in ‘wordexp’.
* Wordexp Example::             A sample program that does word expansion.
* Tilde Expansion::             Details of how tilde expansion works.
* Variable Substitution::       Different types of variable substitution.


File: libc.info,  Node: Expansion Stages,  Next: Calling Wordexp,  Up: Word Expansion

10.4.1 The Stages of Word Expansion
-----------------------------------

When word expansion is applied to a sequence of words, it performs the
following transformations in the order shown here:

  1. "Tilde expansion": Replacement of ‘~foo’ with the name of the home
     directory of ‘foo’.

  2. Next, three different transformations are applied in the same step,
     from left to right:

        • "Variable substitution": Environment variables are substituted
          for references such as ‘$foo’.

        • "Command substitution": Constructs such as ‘`cat foo`’ and the
          equivalent ‘$(cat foo)’ are replaced with the output from the
          inner command.

        • "Arithmetic expansion": Constructs such as ‘$(($x-1))’ are
          replaced with the result of the arithmetic computation.

  3. "Field splitting": subdivision of the text into "words".

  4. "Wildcard expansion": The replacement of a construct such as ‘*.c’
     with a list of ‘.c’ file names.  Wildcard expansion applies to an
     entire word at a time, and replaces that word with 0 or more file
     names that are themselves words.

  5. "Quote removal": The deletion of string-quotes, now that they have
     done their job by inhibiting the above transformations when
     appropriate.

   For the details of these transformations, and how to write the
constructs that use them, see ‘The BASH Manual’ (to appear).


File: libc.info,  Node: Calling Wordexp,  Next: Flags for Wordexp,  Prev: Expansion Stages,  Up: Word Expansion

10.4.2 Calling ‘wordexp’
------------------------

All the functions, constants and data types for word expansion are
declared in the header file ‘wordexp.h’.

   Word expansion produces a vector of words (strings).  To return this
vector, ‘wordexp’ uses a special data type, ‘wordexp_t’, which is a
structure.  You pass ‘wordexp’ the address of the structure, and it
fills in the structure’s fields to tell you about the results.

 -- Data Type: wordexp_t
     This data type holds a pointer to a word vector.  More precisely,
     it records both the address of the word vector and its size.

     ‘we_wordc’
          The number of elements in the vector.

     ‘we_wordv’
          The address of the vector.  This field has type ‘char **’.

     ‘we_offs’
          The offset of the first real element of the vector, from its
          nominal address in the ‘we_wordv’ field.  Unlike the other
          fields, this is always an input to ‘wordexp’, rather than an
          output from it.

          If you use a nonzero offset, then that many elements at the
          beginning of the vector are left empty.  (The ‘wordexp’
          function fills them with null pointers.)

          The ‘we_offs’ field is meaningful only if you use the
          ‘WRDE_DOOFFS’ flag.  Otherwise, the offset is always zero
          regardless of what is in this field, and the first real
          element comes at the beginning of the vector.

 -- Function: int wordexp (const char *WORDS, wordexp_t
          *WORD-VECTOR-PTR, int FLAGS)
     Preliminary: | MT-Unsafe race:utent const:env env sig:ALRM timer
     locale | AS-Unsafe dlopen plugin i18n heap corrupt lock | AC-Unsafe
     corrupt lock fd mem | *Note POSIX Safety Concepts::.

     Perform word expansion on the string WORDS, putting the result in a
     newly allocated vector, and store the size and address of this
     vector into ‘*WORD-VECTOR-PTR’.  The argument FLAGS is a
     combination of bit flags; see *note Flags for Wordexp::, for
     details of the flags.

     You shouldn’t use any of the characters ‘|&;<>’ in the string WORDS
     unless they are quoted; likewise for newline.  If you use these
     characters unquoted, you will get the ‘WRDE_BADCHAR’ error code.
     Don’t use parentheses or braces unless they are quoted or part of a
     word expansion construct.  If you use quotation characters ‘'"`’,
     they should come in pairs that balance.

     The results of word expansion are a sequence of words.  The
     function ‘wordexp’ allocates a string for each resulting word, then
     allocates a vector of type ‘char **’ to store the addresses of
     these strings.  The last element of the vector is a null pointer.
     This vector is called the "word vector".

     To return this vector, ‘wordexp’ stores both its address and its
     length (number of elements, not counting the terminating null
     pointer) into ‘*WORD-VECTOR-PTR’.

     If ‘wordexp’ succeeds, it returns 0.  Otherwise, it returns one of
     these error codes:

     ‘WRDE_BADCHAR’
          The input string WORDS contains an unquoted invalid character
          such as ‘|’.

     ‘WRDE_BADVAL’
          The input string refers to an undefined shell variable, and
          you used the flag ‘WRDE_UNDEF’ to forbid such references.

     ‘WRDE_CMDSUB’
          The input string uses command substitution, and you used the
          flag ‘WRDE_NOCMD’ to forbid command substitution.

     ‘WRDE_NOSPACE’
          It was impossible to allocate memory to hold the result.  In
          this case, ‘wordexp’ can store part of the results—as much as
          it could allocate room for.

     ‘WRDE_SYNTAX’
          There was a syntax error in the input string.  For example, an
          unmatched quoting character is a syntax error.  This error
          code is also used to signal division by zero and overflow in
          arithmetic expansion.

 -- Function: void wordfree (wordexp_t *WORD-VECTOR-PTR)
     Preliminary: | MT-Safe | AS-Unsafe corrupt heap | AC-Unsafe corrupt
     mem | *Note POSIX Safety Concepts::.

     Free the storage used for the word-strings and vector that
     ‘*WORD-VECTOR-PTR’ points to.  This does not free the structure
     ‘*WORD-VECTOR-PTR’ itself—only the other data it points to.


File: libc.info,  Node: Flags for Wordexp,  Next: Wordexp Example,  Prev: Calling Wordexp,  Up: Word Expansion

10.4.3 Flags for Word Expansion
-------------------------------

This section describes the flags that you can specify in the FLAGS
argument to ‘wordexp’.  Choose the flags you want, and combine them with
the C operator ‘|’.

‘WRDE_APPEND’
     Append the words from this expansion to the vector of words
     produced by previous calls to ‘wordexp’.  This way you can
     effectively expand several words as if they were concatenated with
     spaces between them.

     In order for appending to work, you must not modify the contents of
     the word vector structure between calls to ‘wordexp’.  And, if you
     set ‘WRDE_DOOFFS’ in the first call to ‘wordexp’, you must also set
     it when you append to the results.

‘WRDE_DOOFFS’
     Leave blank slots at the beginning of the vector of words.  The
     ‘we_offs’ field says how many slots to leave.  The blank slots
     contain null pointers.

‘WRDE_NOCMD’
     Don’t do command substitution; if the input requests command
     substitution, report an error.

‘WRDE_REUSE’
     Reuse a word vector made by a previous call to ‘wordexp’.  Instead
     of allocating a new vector of words, this call to ‘wordexp’ will
     use the vector that already exists (making it larger if necessary).

     Note that the vector may move, so it is not safe to save an old
     pointer and use it again after calling ‘wordexp’.  You must fetch
     ‘we_pathv’ anew after each call.

‘WRDE_SHOWERR’
     Do show any error messages printed by commands run by command
     substitution.  More precisely, allow these commands to inherit the
     standard error output stream of the current process.  By default,
     ‘wordexp’ gives these commands a standard error stream that
     discards all output.

‘WRDE_UNDEF’
     If the input refers to a shell variable that is not defined, report
     an error.


File: libc.info,  Node: Wordexp Example,  Next: Tilde Expansion,  Prev: Flags for Wordexp,  Up: Word Expansion

10.4.4 ‘wordexp’ Example
------------------------

Here is an example of using ‘wordexp’ to expand several strings and use
the results to run a shell command.  It also shows the use of
‘WRDE_APPEND’ to concatenate the expansions and of ‘wordfree’ to free
the space allocated by ‘wordexp’.

     int
     expand_and_execute (const char *program, const char **options)
     {
       wordexp_t result;
       pid_t pid
       int status, i;

       /* Expand the string for the program to run.  */
       switch (wordexp (program, &result, 0))
         {
         case 0:			/* Successful.  */
           break;
         case WRDE_NOSPACE:
           /* If the error was ‘WRDE_NOSPACE’,
              then perhaps part of the result was allocated.  */
           wordfree (&result);
         default:                    /* Some other error.  */
           return -1;
         }

       /* Expand the strings specified for the arguments.  */
       for (i = 0; options[i] != NULL; i++)
         {
           if (wordexp (options[i], &result, WRDE_APPEND))
             {
               wordfree (&result);
               return -1;
             }
         }

       pid = fork ();
       if (pid == 0)
         {
           /* This is the child process.  Execute the command. */
           execv (result.we_wordv[0], result.we_wordv);
           exit (EXIT_FAILURE);
         }
       else if (pid < 0)
         /* The fork failed.  Report failure.  */
         status = -1;
       else
         /* This is the parent process.  Wait for the child to complete.  */
         if (waitpid (pid, &status, 0) != pid)
           status = -1;

       wordfree (&result);
       return status;
     }


File: libc.info,  Node: Tilde Expansion,  Next: Variable Substitution,  Prev: Wordexp Example,  Up: Word Expansion

10.4.5 Details of Tilde Expansion
---------------------------------

It’s a standard part of shell syntax that you can use ‘~’ at the
beginning of a file name to stand for your own home directory.  You can
use ‘~USER’ to stand for USER’s home directory.

   "Tilde expansion" is the process of converting these abbreviations to
the directory names that they stand for.

   Tilde expansion applies to the ‘~’ plus all following characters up
to whitespace or a slash.  It takes place only at the beginning of a
word, and only if none of the characters to be transformed is quoted in
any way.

   Plain ‘~’ uses the value of the environment variable ‘HOME’ as the
proper home directory name.  ‘~’ followed by a user name uses
‘getpwname’ to look up that user in the user database, and uses whatever
directory is recorded there.  Thus, ‘~’ followed by your own name can
give different results from plain ‘~’, if the value of ‘HOME’ is not
really your home directory.


File: libc.info,  Node: Variable Substitution,  Prev: Tilde Expansion,  Up: Word Expansion

10.4.6 Details of Variable Substitution
---------------------------------------

Part of ordinary shell syntax is the use of ‘$VARIABLE’ to substitute
the value of a shell variable into a command.  This is called "variable
substitution", and it is one part of doing word expansion.

   There are two basic ways you can write a variable reference for
substitution:

‘${VARIABLE}’
     If you write braces around the variable name, then it is completely
     unambiguous where the variable name ends.  You can concatenate
     additional letters onto the end of the variable value by writing
     them immediately after the close brace.  For example, ‘${foo}s’
     expands into ‘tractors’.

‘$VARIABLE’
     If you do not put braces around the variable name, then the
     variable name consists of all the alphanumeric characters and
     underscores that follow the ‘$’.  The next punctuation character
     ends the variable name.  Thus, ‘$foo-bar’ refers to the variable
     ‘foo’ and expands into ‘tractor-bar’.

   When you use braces, you can also use various constructs to modify
the value that is substituted, or test it in various ways.

‘${VARIABLE:-DEFAULT}’
     Substitute the value of VARIABLE, but if that is empty or
     undefined, use DEFAULT instead.

‘${VARIABLE:=DEFAULT}’
     Substitute the value of VARIABLE, but if that is empty or
     undefined, use DEFAULT instead and set the variable to DEFAULT.

‘${VARIABLE:?MESSAGE}’
     If VARIABLE is defined and not empty, substitute its value.

     Otherwise, print MESSAGE as an error message on the standard error
     stream, and consider word expansion a failure.

‘${VARIABLE:+REPLACEMENT}’
     Substitute REPLACEMENT, but only if VARIABLE is defined and
     nonempty.  Otherwise, substitute nothing for this construct.

‘${#VARIABLE}’
     Substitute a numeral which expresses in base ten the number of
     characters in the value of VARIABLE.  ‘${#foo}’ stands for ‘7’,
     because ‘tractor’ is seven characters.

   These variants of variable substitution let you remove part of the
variable’s value before substituting it.  The PREFIX and SUFFIX are not
mere strings; they are wildcard patterns, just like the patterns that
you use to match multiple file names.  But in this context, they match
against parts of the variable value rather than against file names.

‘${VARIABLE%%SUFFIX}’
     Substitute the value of VARIABLE, but first discard from that
     variable any portion at the end that matches the pattern SUFFIX.

     If there is more than one alternative for how to match against
     SUFFIX, this construct uses the longest possible match.

     Thus, ‘${foo%%r*}’ substitutes ‘t’, because the largest match for
     ‘r*’ at the end of ‘tractor’ is ‘ractor’.

‘${VARIABLE%SUFFIX}’
     Substitute the value of VARIABLE, but first discard from that
     variable any portion at the end that matches the pattern SUFFIX.

     If there is more than one alternative for how to match against
     SUFFIX, this construct uses the shortest possible alternative.

     Thus, ‘${foo%r*}’ substitutes ‘tracto’, because the shortest match
     for ‘r*’ at the end of ‘tractor’ is just ‘r’.

‘${VARIABLE##PREFIX}’
     Substitute the value of VARIABLE, but first discard from that
     variable any portion at the beginning that matches the pattern
     PREFIX.

     If there is more than one alternative for how to match against
     PREFIX, this construct uses the longest possible match.

     Thus, ‘${foo##*t}’ substitutes ‘or’, because the largest match for
     ‘*t’ at the beginning of ‘tractor’ is ‘tract’.

‘${VARIABLE#PREFIX}’
     Substitute the value of VARIABLE, but first discard from that
     variable any portion at the beginning that matches the pattern
     PREFIX.

     If there is more than one alternative for how to match against
     PREFIX, this construct uses the shortest possible alternative.

     Thus, ‘${foo#*t}’ substitutes ‘ractor’, because the shortest match
     for ‘*t’ at the beginning of ‘tractor’ is just ‘t’.


File: libc.info,  Node: I/O Overview,  Next: I/O on Streams,  Prev: Pattern Matching,  Up: Top

11 Input/Output Overview
************************

Most programs need to do either input (reading data) or output (writing
data), or most frequently both, in order to do anything useful.  The GNU
C Library provides such a large selection of input and output functions
that the hardest part is often deciding which function is most
appropriate!

   This chapter introduces concepts and terminology relating to input
and output.  Other chapters relating to the GNU I/O facilities are:

   • *note I/O on Streams::, which covers the high-level functions that
     operate on streams, including formatted input and output.

   • *note Low-Level I/O::, which covers the basic I/O and control
     functions on file descriptors.

   • *note File System Interface::, which covers functions for operating
     on directories and for manipulating file attributes such as access
     modes and ownership.

   • *note Pipes and FIFOs::, which includes information on the basic
     interprocess communication facilities.

   • *note Sockets::, which covers a more complicated interprocess
     communication facility with support for networking.

   • *note Low-Level Terminal Interface::, which covers functions for
     changing how input and output to terminals or other serial devices
     are processed.

* Menu:

* I/O Concepts::       Some basic information and terminology.
* File Names::         How to refer to a file.


File: libc.info,  Node: I/O Concepts,  Next: File Names,  Up: I/O Overview

11.1 Input/Output Concepts
==========================

Before you can read or write the contents of a file, you must establish
a connection or communications channel to the file.  This process is
called "opening" the file.  You can open a file for reading, writing, or
both.

   The connection to an open file is represented either as a stream or
as a file descriptor.  You pass this as an argument to the functions
that do the actual read or write operations, to tell them which file to
operate on.  Certain functions expect streams, and others are designed
to operate on file descriptors.

   When you have finished reading to or writing from the file, you can
terminate the connection by "closing" the file.  Once you have closed a
stream or file descriptor, you cannot do any more input or output
operations on it.

* Menu:

* Streams and File Descriptors::    The GNU C Library provides two ways
			             to access the contents of files.
* File Position::                   The number of bytes from the
                                     beginning of the file.


File: libc.info,  Node: Streams and File Descriptors,  Next: File Position,  Up: I/O Concepts

11.1.1 Streams and File Descriptors
-----------------------------------

When you want to do input or output to a file, you have a choice of two
basic mechanisms for representing the connection between your program
and the file: file descriptors and streams.  File descriptors are
represented as objects of type ‘int’, while streams are represented as
‘FILE *’ objects.

   File descriptors provide a primitive, low-level interface to input
and output operations.  Both file descriptors and streams can represent
a connection to a device (such as a terminal), or a pipe or socket for
communicating with another process, as well as a normal file.  But, if
you want to do control operations that are specific to a particular kind
of device, you must use a file descriptor; there are no facilities to
use streams in this way.  You must also use file descriptors if your
program needs to do input or output in special modes, such as
nonblocking (or polled) input (*note File Status Flags::).

   Streams provide a higher-level interface, layered on top of the
primitive file descriptor facilities.  The stream interface treats all
kinds of files pretty much alike—the sole exception being the three
styles of buffering that you can choose (*note Stream Buffering::).

   The main advantage of using the stream interface is that the set of
functions for performing actual input and output operations (as opposed
to control operations) on streams is much richer and more powerful than
the corresponding facilities for file descriptors.  The file descriptor
interface provides only simple functions for transferring blocks of
characters, but the stream interface also provides powerful formatted
input and output functions (‘printf’ and ‘scanf’) as well as functions
for character- and line-oriented input and output.

   Since streams are implemented in terms of file descriptors, you can
extract the file descriptor from a stream and perform low-level
operations directly on the file descriptor.  You can also initially open
a connection as a file descriptor and then make a stream associated with
that file descriptor.

   In general, you should stick with using streams rather than file
descriptors, unless there is some specific operation you want to do that
can only be done on a file descriptor.  If you are a beginning
programmer and aren’t sure what functions to use, we suggest that you
concentrate on the formatted input functions (*note Formatted Input::)
and formatted output functions (*note Formatted Output::).

   If you are concerned about portability of your programs to systems
other than GNU, you should also be aware that file descriptors are not
as portable as streams.  You can expect any system running ISO C to
support streams, but non-GNU systems may not support file descriptors at
all, or may only implement a subset of the GNU functions that operate on
file descriptors.  Most of the file descriptor functions in the GNU C
Library are included in the POSIX.1 standard, however.


File: libc.info,  Node: File Position,  Prev: Streams and File Descriptors,  Up: I/O Concepts

11.1.2 File Position
--------------------

One of the attributes of an open file is its "file position" that keeps
track of where in the file the next character is to be read or written.
On GNU systems, and all POSIX.1 systems, the file position is simply an
integer representing the number of bytes from the beginning of the file.

   The file position is normally set to the beginning of the file when
it is opened, and each time a character is read or written, the file
position is incremented.  In other words, access to the file is normally
"sequential".

   Ordinary files permit read or write operations at any position within
the file.  Some other kinds of files may also permit this.  Files which
do permit this are sometimes referred to as "random-access" files.  You
can change the file position using the ‘fseek’ function on a stream
(*note File Positioning::) or the ‘lseek’ function on a file descriptor
(*note I/O Primitives::).  If you try to change the file position on a
file that doesn’t support random access, you get the ‘ESPIPE’ error.

   Streams and descriptors that are opened for "append access" are
treated specially for output: output to such files is _always_ appended
sequentially to the _end_ of the file, regardless of the file position.
However, the file position is still used to control where in the file
reading is done.

   If you think about it, you’ll realize that several programs can read
a given file at the same time.  In order for each program to be able to
read the file at its own pace, each program must have its own file
pointer, which is not affected by anything the other programs do.

   In fact, each opening of a file creates a separate file position.
Thus, if you open a file twice even in the same program, you get two
streams or descriptors with independent file positions.

   By contrast, if you open a descriptor and then duplicate it to get
another descriptor, these two descriptors share the same file position:
changing the file position of one descriptor will affect the other.


File: libc.info,  Node: File Names,  Prev: I/O Concepts,  Up: I/O Overview

11.2 File Names
===============

In order to open a connection to a file, or to perform other operations
such as deleting a file, you need some way to refer to the file.  Nearly
all files have names that are strings—even files which are actually
devices such as tape drives or terminals.  These strings are called
"file names".  You specify the file name to say which file you want to
open or operate on.

   This section describes the conventions for file names and how the
operating system works with them.

* Menu:

* Directories::                 Directories contain entries for files.
* File Name Resolution::        A file name specifies how to look up a file.
* File Name Errors::            Error conditions relating to file names.
* File Name Portability::       File name portability and syntax issues.


File: libc.info,  Node: Directories,  Next: File Name Resolution,  Up: File Names

11.2.1 Directories
------------------

In order to understand the syntax of file names, you need to understand
how the file system is organized into a hierarchy of directories.

   A "directory" is a file that contains information to associate other
files with names; these associations are called "links" or "directory
entries".  Sometimes, people speak of “files in a directory”, but in
reality, a directory only contains pointers to files, not the files
themselves.

   The name of a file contained in a directory entry is called a "file
name component".  In general, a file name consists of a sequence of one
or more such components, separated by the slash character (‘/’).  A file
name which is just one component names a file with respect to its
directory.  A file name with multiple components names a directory, and
then a file in that directory, and so on.

   Some other documents, such as the POSIX standard, use the term
"pathname" for what we call a file name, and either "filename" or
"pathname component" for what this manual calls a file name component.
We don’t use this terminology because a “path” is something completely
different (a list of directories to search), and we think that
“pathname” used for something else will confuse users.  We always use
“file name” and “file name component” (or sometimes just “component”,
where the context is obvious) in GNU documentation.  Some macros use the
POSIX terminology in their names, such as ‘PATH_MAX’.  These macros are
defined by the POSIX standard, so we cannot change their names.

   You can find more detailed information about operations on
directories in *note File System Interface::.


File: libc.info,  Node: File Name Resolution,  Next: File Name Errors,  Prev: Directories,  Up: File Names

11.2.2 File Name Resolution
---------------------------

A file name consists of file name components separated by slash (‘/’)
characters.  On the systems that the GNU C Library supports, multiple
successive ‘/’ characters are equivalent to a single ‘/’ character.

   The process of determining what file a file name refers to is called
"file name resolution".  This is performed by examining the components
that make up a file name in left-to-right order, and locating each
successive component in the directory named by the previous component.
Of course, each of the files that are referenced as directories must
actually exist, be directories instead of regular files, and have the
appropriate permissions to be accessible by the process; otherwise the
file name resolution fails.

   If a file name begins with a ‘/’, the first component in the file
name is located in the "root directory" of the process (usually all
processes on the system have the same root directory).  Such a file name
is called an "absolute file name".

   Otherwise, the first component in the file name is located in the
current working directory (*note Working Directory::).  This kind of
file name is called a "relative file name".

   The file name components ‘.’ (“dot”) and ‘..’ (“dot-dot”) have
special meanings.  Every directory has entries for these file name
components.  The file name component ‘.’ refers to the directory itself,
while the file name component ‘..’ refers to its "parent directory" (the
directory that contains the link for the directory in question).  As a
special case, ‘..’ in the root directory refers to the root directory
itself, since it has no parent; thus ‘/..’ is the same as ‘/’.

   Here are some examples of file names:

‘/a’
     The file named ‘a’, in the root directory.

‘/a/b’
     The file named ‘b’, in the directory named ‘a’ in the root
     directory.

‘a’
     The file named ‘a’, in the current working directory.

‘/a/./b’
     This is the same as ‘/a/b’.

‘./a’
     The file named ‘a’, in the current working directory.

‘../a’
     The file named ‘a’, in the parent directory of the current working
     directory.

   A file name that names a directory may optionally end in a ‘/’.  You
can specify a file name of ‘/’ to refer to the root directory, but the
empty string is not a meaningful file name.  If you want to refer to the
current working directory, use a file name of ‘.’ or ‘./’.

   Unlike some other operating systems, GNU systems don’t have any
built-in support for file types (or extensions) or file versions as part
of its file name syntax.  Many programs and utilities use conventions
for file names—for example, files containing C source code usually have
names suffixed with ‘.c’—but there is nothing in the file system itself
that enforces this kind of convention.


File: libc.info,  Node: File Name Errors,  Next: File Name Portability,  Prev: File Name Resolution,  Up: File Names

11.2.3 File Name Errors
-----------------------

Functions that accept file name arguments usually detect these ‘errno’
error conditions relating to the file name syntax or trouble finding the
named file.  These errors are referred to throughout this manual as the
"usual file name errors".

‘EACCES’
     The process does not have search permission for a directory
     component of the file name.

‘ENAMETOOLONG’
     This error is used when either the total length of a file name is
     greater than ‘PATH_MAX’, or when an individual file name component
     has a length greater than ‘NAME_MAX’.  *Note Limits for Files::.

     On GNU/Hurd systems, there is no imposed limit on overall file name
     length, but some file systems may place limits on the length of a
     component.

‘ENOENT’
     This error is reported when a file referenced as a directory
     component in the file name doesn’t exist, or when a component is a
     symbolic link whose target file does not exist.  *Note Symbolic
     Links::.

‘ENOTDIR’
     A file that is referenced as a directory component in the file name
     exists, but it isn’t a directory.

‘ELOOP’
     Too many symbolic links were resolved while trying to look up the
     file name.  The system has an arbitrary limit on the number of
     symbolic links that may be resolved in looking up a single file
     name, as a primitive way to detect loops.  *Note Symbolic Links::.


File: libc.info,  Node: File Name Portability,  Prev: File Name Errors,  Up: File Names

11.2.4 Portability of File Names
--------------------------------

The rules for the syntax of file names discussed in *note File Names::,
are the rules normally used by GNU systems and by other POSIX systems.
However, other operating systems may use other conventions.

   There are two reasons why it can be important for you to be aware of
file name portability issues:

   • If your program makes assumptions about file name syntax, or
     contains embedded literal file name strings, it is more difficult
     to get it to run under other operating systems that use different
     syntax conventions.

   • Even if you are not concerned about running your program on
     machines that run other operating systems, it may still be possible
     to access files that use different naming conventions.  For
     example, you may be able to access file systems on another computer
     running a different operating system over a network, or read and
     write disks in formats used by other operating systems.

   The ISO C standard says very little about file name syntax, only that
file names are strings.  In addition to varying restrictions on the
length of file names and what characters can validly appear in a file
name, different operating systems use different conventions and syntax
for concepts such as structured directories and file types or
extensions.  Some concepts such as file versions might be supported in
some operating systems and not by others.

   The POSIX.1 standard allows implementations to put additional
restrictions on file name syntax, concerning what characters are
permitted in file names and on the length of file name and file name
component strings.  However, on GNU systems, any character except the
null character is permitted in a file name string, and on GNU/Hurd
systems there are no limits on the length of file name strings.


File: libc.info,  Node: I/O on Streams,  Next: Low-Level I/O,  Prev: I/O Overview,  Up: Top

12 Input/Output on Streams
**************************

This chapter describes the functions for creating streams and performing
input and output operations on them.  As discussed in *note I/O
Overview::, a stream is a fairly abstract, high-level concept
representing a communications channel to a file, device, or process.

* Menu:

* Streams::                     About the data type representing a stream.
* Standard Streams::            Streams to the standard input and output
				 devices are created for you.
* Opening Streams::             How to create a stream to talk to a file.
* Closing Streams::             Close a stream when you are finished with it.
* Streams and Threads::         Issues with streams in threaded programs.
* Streams and I18N::            Streams in internationalized applications.
* Simple Output::               Unformatted output by characters and lines.
* Character Input::             Unformatted input by characters and words.
* Line Input::                  Reading a line or a record from a stream.
* Unreading::                   Peeking ahead/pushing back input just read.
* Block Input/Output::          Input and output operations on blocks of data.
* Formatted Output::            ‘printf’ and related functions.
* Customizing Printf::          You can define new conversion specifiers for
				 ‘printf’ and friends.
* Formatted Input::             ‘scanf’ and related functions.
* EOF and Errors::              How you can tell if an I/O error happens.
* Error Recovery::		What you can do about errors.
* Binary Streams::              Some systems distinguish between text files
				 and binary files.
* File Positioning::            About random-access streams.
* Portable Positioning::        Random access on peculiar ISO C systems.
* Stream Buffering::            How to control buffering of streams.
* Other Kinds of Streams::      Streams that do not necessarily correspond
				 to an open file.
* Formatted Messages::          Print strictly formatted messages.


File: libc.info,  Node: Streams,  Next: Standard Streams,  Up: I/O on Streams

12.1 Streams
============

For historical reasons, the type of the C data structure that represents
a stream is called ‘FILE’ rather than “stream”.  Since most of the
library functions deal with objects of type ‘FILE *’, sometimes the term
"file pointer" is also used to mean “stream”.  This leads to unfortunate
confusion over terminology in many books on C. This manual, however, is
careful to use the terms “file” and “stream” only in the technical
sense.

   The ‘FILE’ type is declared in the header file ‘stdio.h’.

 -- Data Type: FILE
     This is the data type used to represent stream objects.  A ‘FILE’
     object holds all of the internal state information about the
     connection to the associated file, including such things as the
     file position indicator and buffering information.  Each stream
     also has error and end-of-file status indicators that can be tested
     with the ‘ferror’ and ‘feof’ functions; see *note EOF and Errors::.

   ‘FILE’ objects are allocated and managed internally by the
input/output library functions.  Don’t try to create your own objects of
type ‘FILE’; let the library do it.  Your programs should deal only with
pointers to these objects (that is, ‘FILE *’ values) rather than the
objects themselves.


File: libc.info,  Node: Standard Streams,  Next: Opening Streams,  Prev: Streams,  Up: I/O on Streams

12.2 Standard Streams
=====================

When the ‘main’ function of your program is invoked, it already has
three predefined streams open and available for use.  These represent
the “standard” input and output channels that have been established for
the process.

   These streams are declared in the header file ‘stdio.h’.

 -- Variable: FILE * stdin
     The "standard input" stream, which is the normal source of input
     for the program.

 -- Variable: FILE * stdout
     The "standard output" stream, which is used for normal output from
     the program.

 -- Variable: FILE * stderr
     The "standard error" stream, which is used for error messages and
     diagnostics issued by the program.

   On GNU systems, you can specify what files or processes correspond to
these streams using the pipe and redirection facilities provided by the
shell.  (The primitives shells use to implement these facilities are
described in *note File System Interface::.)  Most other operating
systems provide similar mechanisms, but the details of how to use them
can vary.

   In the GNU C Library, ‘stdin’, ‘stdout’, and ‘stderr’ are normal
variables which you can set just like any others.  For example, to
redirect the standard output to a file, you could do:

     fclose (stdout);
     stdout = fopen ("standard-output-file", "w");

   Note however, that in other systems ‘stdin’, ‘stdout’, and ‘stderr’
are macros that you cannot assign to in the normal way.  But you can use
‘freopen’ to get the effect of closing one and reopening it.  *Note
Opening Streams::.

   The three streams ‘stdin’, ‘stdout’, and ‘stderr’ are not unoriented
at program start (*note Streams and I18N::).


File: libc.info,  Node: Opening Streams,  Next: Closing Streams,  Prev: Standard Streams,  Up: I/O on Streams

12.3 Opening Streams
====================

Opening a file with the ‘fopen’ function creates a new stream and
establishes a connection between the stream and a file.  This may
involve creating a new file.

   Everything described in this section is declared in the header file
‘stdio.h’.

 -- Function: FILE * fopen (const char *FILENAME, const char *OPENTYPE)
     Preliminary: | MT-Safe | AS-Unsafe heap lock | AC-Unsafe mem fd
     lock | *Note POSIX Safety Concepts::.

     The ‘fopen’ function opens a stream for I/O to the file FILENAME,
     and returns a pointer to the stream.

     The OPENTYPE argument is a string that controls how the file is
     opened and specifies attributes of the resulting stream.  It must
     begin with one of the following sequences of characters:

     ‘r’
          Open an existing file for reading only.

     ‘w’
          Open the file for writing only.  If the file already exists,
          it is truncated to zero length.  Otherwise a new file is
          created.

     ‘a’
          Open a file for append access; that is, writing at the end of
          file only.  If the file already exists, its initial contents
          are unchanged and output to the stream is appended to the end
          of the file.  Otherwise, a new, empty file is created.

     ‘r+’
          Open an existing file for both reading and writing.  The
          initial contents of the file are unchanged and the initial
          file position is at the beginning of the file.

     ‘w+’
          Open a file for both reading and writing.  If the file already
          exists, it is truncated to zero length.  Otherwise, a new file
          is created.

     ‘a+’
          Open or create file for both reading and appending.  If the
          file exists, its initial contents are unchanged.  Otherwise, a
          new file is created.  The initial file position for reading is
          at the beginning of the file, but output is always appended to
          the end of the file.

     As you can see, ‘+’ requests a stream that can do both input and
     output.  When using such a stream, you must call ‘fflush’ (*note
     Stream Buffering::) or a file positioning function such as ‘fseek’
     (*note File Positioning::) when switching from reading to writing
     or vice versa.  Otherwise, internal buffers might not be emptied
     properly.

     Additional characters may appear after these to specify flags for
     the call.  Always put the mode (‘r’, ‘w+’, etc.)  first; that is
     the only part you are guaranteed will be understood by all systems.

     The GNU C Library defines additional characters for use in
     OPENTYPE:

     ‘c’
          The file is opened with cancellation in the I/O functions
          disabled.

     ‘e’
          The underlying file descriptor will be closed if you use any
          of the ‘exec…’ functions (*note Executing a File::).  (This is
          equivalent to having set ‘FD_CLOEXEC’ on that descriptor.
          *Note Descriptor Flags::.)

     ‘m’
          The file is opened and accessed using ‘mmap’.  This is only
          supported with files opened for reading.

     ‘x’
          Insist on creating a new file—if a file FILENAME already
          exists, ‘fopen’ fails rather than opening it.  If you use ‘x’
          you are guaranteed that you will not clobber an existing file.
          This is equivalent to the ‘O_EXCL’ option to the ‘open’
          function (*note Opening and Closing Files::).

          The ‘x’ modifier is part of ISO C11.

     The character ‘b’ in OPENTYPE has a standard meaning; it requests a
     binary stream rather than a text stream.  But this makes no
     difference in POSIX systems (including GNU systems).  If both ‘+’
     and ‘b’ are specified, they can appear in either order.  *Note
     Binary Streams::.

     If the OPENTYPE string contains the sequence ‘,ccs=STRING’ then
     STRING is taken as the name of a coded character set and ‘fopen’
     will mark the stream as wide-oriented with appropriate conversion
     functions in place to convert from and to the character set STRING.
     Any other stream is opened initially unoriented and the orientation
     is decided with the first file operation.  If the first operation
     is a wide character operation, the stream is not only marked as
     wide-oriented, also the conversion functions to convert to the
     coded character set used for the current locale are loaded.  This
     will not change anymore from this point on even if the locale
     selected for the ‘LC_CTYPE’ category is changed.

     Any other characters in OPENTYPE are simply ignored.  They may be
     meaningful in other systems.

     If the open fails, ‘fopen’ returns a null pointer.

     When the sources are compiled with ‘_FILE_OFFSET_BITS == 64’ on a
     32 bit machine this function is in fact ‘fopen64’ since the LFS
     interface replaces transparently the old interface.

   You can have multiple streams (or file descriptors) pointing to the
same file open at the same time.  If you do only input, this works
straightforwardly, but you must be careful if any output streams are
included.  *Note Stream/Descriptor Precautions::.  This is equally true
whether the streams are in one program (not usual) or in several
programs (which can easily happen).  It may be advantageous to use the
file locking facilities to avoid simultaneous access.  *Note File
Locks::.

 -- Function: FILE * fopen64 (const char *FILENAME, const char
          *OPENTYPE)
     Preliminary: | MT-Safe | AS-Unsafe heap lock | AC-Unsafe mem fd
     lock | *Note POSIX Safety Concepts::.

     This function is similar to ‘fopen’ but the stream it returns a
     pointer for is opened using ‘open64’.  Therefore this stream can be
     used even on files larger than 2^31 bytes on 32 bit machines.

     Please note that the return type is still ‘FILE *’.  There is no
     special ‘FILE’ type for the LFS interface.

     If the sources are compiled with ‘_FILE_OFFSET_BITS == 64’ on a 32
     bits machine this function is available under the name ‘fopen’ and
     so transparently replaces the old interface.

 -- Macro: int FOPEN_MAX
     The value of this macro is an integer constant expression that
     represents the minimum number of streams that the implementation
     guarantees can be open simultaneously.  You might be able to open
     more than this many streams, but that is not guaranteed.  The value
     of this constant is at least eight, which includes the three
     standard streams ‘stdin’, ‘stdout’, and ‘stderr’.  In POSIX.1
     systems this value is determined by the ‘OPEN_MAX’ parameter; *note
     General Limits::.  In BSD and GNU, it is controlled by the
     ‘RLIMIT_NOFILE’ resource limit; *note Limits on Resources::.

 -- Function: FILE * freopen (const char *FILENAME, const char
          *OPENTYPE, FILE *STREAM)
     Preliminary: | MT-Safe | AS-Unsafe corrupt | AC-Unsafe corrupt fd |
     *Note POSIX Safety Concepts::.

     This function is like a combination of ‘fclose’ and ‘fopen’.  It
     first closes the stream referred to by STREAM, ignoring any errors
     that are detected in the process.  (Because errors are ignored, you
     should not use ‘freopen’ on an output stream if you have actually
     done any output using the stream.)  Then the file named by FILENAME
     is opened with mode OPENTYPE as for ‘fopen’, and associated with
     the same stream object STREAM.

     If the operation fails, a null pointer is returned; otherwise,
     ‘freopen’ returns STREAM.

     ‘freopen’ has traditionally been used to connect a standard stream
     such as ‘stdin’ with a file of your own choice.  This is useful in
     programs in which use of a standard stream for certain purposes is
     hard-coded.  In the GNU C Library, you can simply close the
     standard streams and open new ones with ‘fopen’.  But other systems
     lack this ability, so using ‘freopen’ is more portable.

     When the sources are compiled with ‘_FILE_OFFSET_BITS == 64’ on a
     32 bit machine this function is in fact ‘freopen64’ since the LFS
     interface replaces transparently the old interface.

 -- Function: FILE * freopen64 (const char *FILENAME, const char
          *OPENTYPE, FILE *STREAM)
     Preliminary: | MT-Safe | AS-Unsafe corrupt | AC-Unsafe corrupt fd |
     *Note POSIX Safety Concepts::.

     This function is similar to ‘freopen’.  The only difference is that
     on 32 bit machine the stream returned is able to read beyond the
     2^31 bytes limits imposed by the normal interface.  It should be
     noted that the stream pointed to by STREAM need not be opened using
     ‘fopen64’ or ‘freopen64’ since its mode is not important for this
     function.

     If the sources are compiled with ‘_FILE_OFFSET_BITS == 64’ on a 32
     bits machine this function is available under the name ‘freopen’
     and so transparently replaces the old interface.

   In some situations it is useful to know whether a given stream is
available for reading or writing.  This information is normally not
available and would have to be remembered separately.  Solaris
introduced a few functions to get this information from the stream
descriptor and these functions are also available in the GNU C Library.

 -- Function: int __freadable (FILE *STREAM)
     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     The ‘__freadable’ function determines whether the stream STREAM was
     opened to allow reading.  In this case the return value is nonzero.
     For write-only streams the function returns zero.

     This function is declared in ‘stdio_ext.h’.

 -- Function: int __fwritable (FILE *STREAM)
     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     The ‘__fwritable’ function determines whether the stream STREAM was
     opened to allow writing.  In this case the return value is nonzero.
     For read-only streams the function returns zero.

     This function is declared in ‘stdio_ext.h’.

   For slightly different kinds of problems there are two more
functions.  They provide even finer-grained information.

 -- Function: int __freading (FILE *STREAM)
     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     The ‘__freading’ function determines whether the stream STREAM was
     last read from or whether it is opened read-only.  In this case the
     return value is nonzero, otherwise it is zero.  Determining whether
     a stream opened for reading and writing was last used for writing
     allows to draw conclusions about the content about the buffer,
     among other things.

     This function is declared in ‘stdio_ext.h’.

 -- Function: int __fwriting (FILE *STREAM)
     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     The ‘__fwriting’ function determines whether the stream STREAM was
     last written to or whether it is opened write-only.  In this case
     the return value is nonzero, otherwise it is zero.

     This function is declared in ‘stdio_ext.h’.


File: libc.info,  Node: Closing Streams,  Next: Streams and Threads,  Prev: Opening Streams,  Up: I/O on Streams

12.4 Closing Streams
====================

When a stream is closed with ‘fclose’, the connection between the stream
and the file is canceled.  After you have closed a stream, you cannot
perform any additional operations on it.

 -- Function: int fclose (FILE *STREAM)
     Preliminary: | MT-Safe | AS-Unsafe heap lock | AC-Unsafe lock mem
     fd | *Note POSIX Safety Concepts::.

     This function causes STREAM to be closed and the connection to the
     corresponding file to be broken.  Any buffered output is written
     and any buffered input is discarded.  The ‘fclose’ function returns
     a value of ‘0’ if the file was closed successfully, and ‘EOF’ if an
     error was detected.

     It is important to check for errors when you call ‘fclose’ to close
     an output stream, because real, everyday errors can be detected at
     this time.  For example, when ‘fclose’ writes the remaining
     buffered output, it might get an error because the disk is full.
     Even if you know the buffer is empty, errors can still occur when
     closing a file if you are using NFS.

     The function ‘fclose’ is declared in ‘stdio.h’.

   To close all streams currently available the GNU C Library provides
another function.

 -- Function: int fcloseall (void)
     Preliminary: | MT-Unsafe race:streams | AS-Unsafe | AC-Safe | *Note
     POSIX Safety Concepts::.

     This function causes all open streams of the process to be closed
     and the connections to corresponding files to be broken.  All
     buffered data is written and any buffered input is discarded.  The
     ‘fcloseall’ function returns a value of ‘0’ if all the files were
     closed successfully, and ‘EOF’ if an error was detected.

     This function should be used only in special situations, e.g., when
     an error occurred and the program must be aborted.  Normally each
     single stream should be closed separately so that problems with
     individual streams can be identified.  It is also problematic since
     the standard streams (*note Standard Streams::) will also be
     closed.

     The function ‘fcloseall’ is declared in ‘stdio.h’.

   If the ‘main’ function to your program returns, or if you call the
‘exit’ function (*note Normal Termination::), all open streams are
automatically closed properly.  If your program terminates in any other
manner, such as by calling the ‘abort’ function (*note Aborting a
Program::) or from a fatal signal (*note Signal Handling::), open
streams might not be closed properly.  Buffered output might not be
flushed and files may be incomplete.  For more information on buffering
of streams, see *note Stream Buffering::.


File: libc.info,  Node: Streams and Threads,  Next: Streams and I18N,  Prev: Closing Streams,  Up: I/O on Streams

12.5 Streams and Threads
========================

Streams can be used in multi-threaded applications in the same way they
are used in single-threaded applications.  But the programmer must be
aware of the possible complications.  It is important to know about
these also if the program one writes never use threads since the design
and implementation of many stream functions are heavily influenced by
the requirements added by multi-threaded programming.

   The POSIX standard requires that by default the stream operations are
atomic.  I.e., issuing two stream operations for the same stream in two
threads at the same time will cause the operations to be executed as if
they were issued sequentially.  The buffer operations performed while
reading or writing are protected from other uses of the same stream.  To
do this each stream has an internal lock object which has to be
(implicitly) acquired before any work can be done.

   But there are situations where this is not enough and there are also
situations where this is not wanted.  The implicit locking is not enough
if the program requires more than one stream function call to happen
atomically.  One example would be if an output line a program wants to
generate is created by several function calls.  The functions by
themselves would ensure only atomicity of their own operation, but not
atomicity over all the function calls.  For this it is necessary to
perform the stream locking in the application code.

 -- Function: void flockfile (FILE *STREAM)
     Preliminary: | MT-Safe | AS-Safe | AC-Unsafe lock | *Note POSIX
     Safety Concepts::.

     The ‘flockfile’ function acquires the internal locking object
     associated with the stream STREAM.  This ensures that no other
     thread can explicitly through ‘flockfile’/‘ftrylockfile’ or
     implicitly through the call of a stream function lock the stream.
     The thread will block until the lock is acquired.  An explicit call
     to ‘funlockfile’ has to be used to release the lock.

 -- Function: int ftrylockfile (FILE *STREAM)
     Preliminary: | MT-Safe | AS-Safe | AC-Unsafe lock | *Note POSIX
     Safety Concepts::.

     The ‘ftrylockfile’ function tries to acquire the internal locking
     object associated with the stream STREAM just like ‘flockfile’.
     But unlike ‘flockfile’ this function does not block if the lock is
     not available.  ‘ftrylockfile’ returns zero if the lock was
     successfully acquired.  Otherwise the stream is locked by another
     thread.

 -- Function: void funlockfile (FILE *STREAM)
     Preliminary: | MT-Safe | AS-Safe | AC-Unsafe lock | *Note POSIX
     Safety Concepts::.

     The ‘funlockfile’ function releases the internal locking object of
     the stream STREAM.  The stream must have been locked before by a
     call to ‘flockfile’ or a successful call of ‘ftrylockfile’.  The
     implicit locking performed by the stream operations do not count.
     The ‘funlockfile’ function does not return an error status and the
     behavior of a call for a stream which is not locked by the current
     thread is undefined.

   The following example shows how the functions above can be used to
generate an output line atomically even in multi-threaded applications
(yes, the same job could be done with one ‘fprintf’ call but it is
sometimes not possible):

     FILE *fp;
     {
        …
        flockfile (fp);
        fputs ("This is test number ", fp);
        fprintf (fp, "%d\n", test);
        funlockfile (fp)
     }

   Without the explicit locking it would be possible for another thread
to use the stream FP after the ‘fputs’ call returns and before ‘fprintf’
was called with the result that the number does not follow the word
‘number’.

   From this description it might already be clear that the locking
objects in streams are no simple mutexes.  Since locking the same stream
twice in the same thread is allowed the locking objects must be
equivalent to recursive mutexes.  These mutexes keep track of the owner
and the number of times the lock is acquired.  The same number of
‘funlockfile’ calls by the same threads is necessary to unlock the
stream completely.  For instance:

     void
     foo (FILE *fp)
     {
       ftrylockfile (fp);
       fputs ("in foo\n", fp);
       /* This is very wrong!!!  */
       funlockfile (fp);
     }

   It is important here that the ‘funlockfile’ function is only called
if the ‘ftrylockfile’ function succeeded in locking the stream.  It is
therefore always wrong to ignore the result of ‘ftrylockfile’.  And it
makes no sense since otherwise one would use ‘flockfile’.  The result of
code like that above is that either ‘funlockfile’ tries to free a stream
that hasn’t been locked by the current thread or it frees the stream
prematurely.  The code should look like this:

     void
     foo (FILE *fp)
     {
       if (ftrylockfile (fp) == 0)
         {
           fputs ("in foo\n", fp);
           funlockfile (fp);
         }
     }

   Now that we covered why it is necessary to have locking it is
necessary to talk about situations when locking is unwanted and what can
be done.  The locking operations (explicit or implicit) don’t come for
free.  Even if a lock is not taken the cost is not zero.  The operations
which have to be performed require memory operations that are safe in
multi-processor environments.  With the many local caches involved in
such systems this is quite costly.  So it is best to avoid the locking
completely if it is not needed – because the code in question is never
used in a context where two or more threads may use a stream at a time.
This can be determined most of the time for application code; for
library code which can be used in many contexts one should default to be
conservative and use locking.

   There are two basic mechanisms to avoid locking.  The first is to use
the ‘_unlocked’ variants of the stream operations.  The POSIX standard
defines quite a few of those and the GNU C Library adds a few more.
These variants of the functions behave just like the functions with the
name without the suffix except that they do not lock the stream.  Using
these functions is very desirable since they are potentially much
faster.  This is not only because the locking operation itself is
avoided.  More importantly, functions like ‘putc’ and ‘getc’ are very
simple and traditionally (before the introduction of threads) were
implemented as macros which are very fast if the buffer is not empty.
With the addition of locking requirements these functions are no longer
implemented as macros since they would expand to too much code.  But
these macros are still available with the same functionality under the
new names ‘putc_unlocked’ and ‘getc_unlocked’.  This possibly huge
difference of speed also suggests the use of the ‘_unlocked’ functions
even if locking is required.  The difference is that the locking then
has to be performed in the program:

     void
     foo (FILE *fp, char *buf)
     {
       flockfile (fp);
       while (*buf != '/')
         putc_unlocked (*buf++, fp);
       funlockfile (fp);
     }

   If in this example the ‘putc’ function would be used and the explicit
locking would be missing the ‘putc’ function would have to acquire the
lock in every call, potentially many times depending on when the loop
terminates.  Writing it the way illustrated above allows the
‘putc_unlocked’ macro to be used which means no locking and direct
manipulation of the buffer of the stream.

   A second way to avoid locking is by using a non-standard function
which was introduced in Solaris and is available in the GNU C Library as
well.

 -- Function: int __fsetlocking (FILE *STREAM, int TYPE)
     Preliminary: | MT-Safe race:stream | AS-Unsafe lock | AC-Safe |
     *Note POSIX Safety Concepts::.

     The ‘__fsetlocking’ function can be used to select whether the
     stream operations will implicitly acquire the locking object of the
     stream STREAM.  By default this is done but it can be disabled and
     reinstated using this function.  There are three values defined for
     the TYPE parameter.

     ‘FSETLOCKING_INTERNAL’
          The stream ‘stream’ will from now on use the default internal
          locking.  Every stream operation with exception of the
          ‘_unlocked’ variants will implicitly lock the stream.

     ‘FSETLOCKING_BYCALLER’
          After the ‘__fsetlocking’ function returns, the user is
          responsible for locking the stream.  None of the stream
          operations will implicitly do this anymore until the state is
          set back to ‘FSETLOCKING_INTERNAL’.

     ‘FSETLOCKING_QUERY’
          ‘__fsetlocking’ only queries the current locking state of the
          stream.  The return value will be ‘FSETLOCKING_INTERNAL’ or
          ‘FSETLOCKING_BYCALLER’ depending on the state.

     The return value of ‘__fsetlocking’ is either
     ‘FSETLOCKING_INTERNAL’ or ‘FSETLOCKING_BYCALLER’ depending on the
     state of the stream before the call.

     This function and the values for the TYPE parameter are declared in
     ‘stdio_ext.h’.

   This function is especially useful when program code has to be used
which is written without knowledge about the ‘_unlocked’ functions (or
if the programmer was too lazy to use them).


File: libc.info,  Node: Streams and I18N,  Next: Simple Output,  Prev: Streams and Threads,  Up: I/O on Streams

12.6 Streams in Internationalized Applications
==============================================

ISO C90 introduced the new type ‘wchar_t’ to allow handling larger
character sets.  What was missing was a possibility to output strings of
‘wchar_t’ directly.  One had to convert them into multibyte strings
using ‘mbstowcs’ (there was no ‘mbsrtowcs’ yet) and then use the normal
stream functions.  While this is doable it is very cumbersome since
performing the conversions is not trivial and greatly increases program
complexity and size.

   The Unix standard early on (I think in XPG4.2) introduced two
additional format specifiers for the ‘printf’ and ‘scanf’ families of
functions.  Printing and reading of single wide characters was made
possible using the ‘%C’ specifier and wide character strings can be
handled with ‘%S’.  These modifiers behave just like ‘%c’ and ‘%s’ only
that they expect the corresponding argument to have the wide character
type and that the wide character and string are transformed into/from
multibyte strings before being used.

   This was a beginning but it is still not good enough.  Not always is
it desirable to use ‘printf’ and ‘scanf’.  The other, smaller and faster
functions cannot handle wide characters.  Second, it is not possible to
have a format string for ‘printf’ and ‘scanf’ consisting of wide
characters.  The result is that format strings would have to be
generated if they have to contain non-basic characters.

   In the Amendment 1 to ISO C90 a whole new set of functions was added
to solve the problem.  Most of the stream functions got a counterpart
which take a wide character or wide character string instead of a
character or string respectively.  The new functions operate on the same
streams (like ‘stdout’).  This is different from the model of the C++
runtime library where separate streams for wide and normal I/O are used.

   Being able to use the same stream for wide and normal operations
comes with a restriction: a stream can be used either for wide
operations or for normal operations.  Once it is decided there is no way
back.  Only a call to ‘freopen’ or ‘freopen64’ can reset the
"orientation".  The orientation can be decided in three ways:

   • If any of the normal character functions are used (this includes
     the ‘fread’ and ‘fwrite’ functions) the stream is marked as not
     wide oriented.

   • If any of the wide character functions are used the stream is
     marked as wide oriented.

   • The ‘fwide’ function can be used to set the orientation either way.

   It is important to never mix the use of wide and not wide operations
on a stream.  There are no diagnostics issued.  The application behavior
will simply be strange or the application will simply crash.  The
‘fwide’ function can help avoid this.

 -- Function: int fwide (FILE *STREAM, int MODE)
     Preliminary: | MT-Safe | AS-Unsafe corrupt | AC-Unsafe lock | *Note
     POSIX Safety Concepts::.

     The ‘fwide’ function can be used to set and query the state of the
     orientation of the stream STREAM.  If the MODE parameter has a
     positive value the streams get wide oriented, for negative values
     narrow oriented.  It is not possible to overwrite previous
     orientations with ‘fwide’.  I.e., if the stream STREAM was already
     oriented before the call nothing is done.

     If MODE is zero the current orientation state is queried and
     nothing is changed.

     The ‘fwide’ function returns a negative value, zero, or a positive
     value if the stream is narrow, not at all, or wide oriented
     respectively.

     This function was introduced in Amendment 1 to ISO C90 and is
     declared in ‘wchar.h’.

   It is generally a good idea to orient a stream as early as possible.
This can prevent surprise especially for the standard streams ‘stdin’,
‘stdout’, and ‘stderr’.  If some library function in some situations
uses one of these streams and this use orients the stream in a different
way the rest of the application expects it one might end up with hard to
reproduce errors.  Remember that no errors are signal if the streams are
used incorrectly.  Leaving a stream unoriented after creation is
normally only necessary for library functions which create streams which
can be used in different contexts.

   When writing code which uses streams and which can be used in
different contexts it is important to query the orientation of the
stream before using it (unless the rules of the library interface demand
a specific orientation).  The following little, silly function
illustrates this.

     void
     print_f (FILE *fp)
     {
       if (fwide (fp, 0) > 0)
         /* Positive return value means wide orientation.  */
         fputwc (L'f', fp);
       else
         fputc ('f', fp);
     }

   Note that in this case the function ‘print_f’ decides about the
orientation of the stream if it was unoriented before (will not happen
if the advice above is followed).

   The encoding used for the ‘wchar_t’ values is unspecified and the
user must not make any assumptions about it.  For I/O of ‘wchar_t’
values this means that it is impossible to write these values directly
to the stream.  This is not what follows from the ISO C locale model
either.  What happens instead is that the bytes read from or written to
the underlying media are first converted into the internal encoding
chosen by the implementation for ‘wchar_t’.  The external encoding is
determined by the ‘LC_CTYPE’ category of the current locale or by the
‘ccs’ part of the mode specification given to ‘fopen’, ‘fopen64’,
‘freopen’, or ‘freopen64’.  How and when the conversion happens is
unspecified and it happens invisibly to the user.

   Since a stream is created in the unoriented state it has at that
point no conversion associated with it.  The conversion which will be
used is determined by the ‘LC_CTYPE’ category selected at the time the
stream is oriented.  If the locales are changed at the runtime this
might produce surprising results unless one pays attention.  This is
just another good reason to orient the stream explicitly as soon as
possible, perhaps with a call to ‘fwide’.


File: libc.info,  Node: Simple Output,  Next: Character Input,  Prev: Streams and I18N,  Up: I/O on Streams

12.7 Simple Output by Characters or Lines
=========================================

This section describes functions for performing character- and
line-oriented output.

   These narrow stream functions are declared in the header file
‘stdio.h’ and the wide stream functions in ‘wchar.h’.

 -- Function: int fputc (int C, FILE *STREAM)
     Preliminary: | MT-Safe | AS-Unsafe corrupt | AC-Unsafe corrupt lock
     | *Note POSIX Safety Concepts::.

     The ‘fputc’ function converts the character C to type ‘unsigned
     char’, and writes it to the stream STREAM.  ‘EOF’ is returned if a
     write error occurs; otherwise the character C is returned.

 -- Function: wint_t fputwc (wchar_t WC, FILE *STREAM)
     Preliminary: | MT-Safe | AS-Unsafe corrupt | AC-Unsafe corrupt lock
     | *Note POSIX Safety Concepts::.

     The ‘fputwc’ function writes the wide character WC to the stream
     STREAM.  ‘WEOF’ is returned if a write error occurs; otherwise the
     character WC is returned.

 -- Function: int fputc_unlocked (int C, FILE *STREAM)
     Preliminary: | MT-Safe race:stream | AS-Unsafe corrupt | AC-Unsafe
     corrupt | *Note POSIX Safety Concepts::.

     The ‘fputc_unlocked’ function is equivalent to the ‘fputc’ function
     except that it does not implicitly lock the stream.

 -- Function: wint_t fputwc_unlocked (wchar_t WC, FILE *STREAM)
     Preliminary: | MT-Safe race:stream | AS-Unsafe corrupt | AC-Unsafe
     corrupt | *Note POSIX Safety Concepts::.

     The ‘fputwc_unlocked’ function is equivalent to the ‘fputwc’
     function except that it does not implicitly lock the stream.

     This function is a GNU extension.

 -- Function: int putc (int C, FILE *STREAM)
     Preliminary: | MT-Safe | AS-Unsafe corrupt | AC-Unsafe corrupt lock
     | *Note POSIX Safety Concepts::.

     This is just like ‘fputc’, except that most systems implement it as
     a macro, making it faster.  One consequence is that it may evaluate
     the STREAM argument more than once, which is an exception to the
     general rule for macros.  ‘putc’ is usually the best function to
     use for writing a single character.

 -- Function: wint_t putwc (wchar_t WC, FILE *STREAM)
     Preliminary: | MT-Safe | AS-Unsafe corrupt | AC-Unsafe corrupt lock
     | *Note POSIX Safety Concepts::.

     This is just like ‘fputwc’, except that it can be implement as a
     macro, making it faster.  One consequence is that it may evaluate
     the STREAM argument more than once, which is an exception to the
     general rule for macros.  ‘putwc’ is usually the best function to
     use for writing a single wide character.

 -- Function: int putc_unlocked (int C, FILE *STREAM)
     Preliminary: | MT-Safe race:stream | AS-Unsafe corrupt | AC-Unsafe
     corrupt | *Note POSIX Safety Concepts::.

     The ‘putc_unlocked’ function is equivalent to the ‘putc’ function
     except that it does not implicitly lock the stream.

 -- Function: wint_t putwc_unlocked (wchar_t WC, FILE *STREAM)
     Preliminary: | MT-Safe race:stream | AS-Unsafe corrupt | AC-Unsafe
     corrupt | *Note POSIX Safety Concepts::.

     The ‘putwc_unlocked’ function is equivalent to the ‘putwc’ function
     except that it does not implicitly lock the stream.

     This function is a GNU extension.

 -- Function: int putchar (int C)
     Preliminary: | MT-Safe | AS-Unsafe corrupt | AC-Unsafe corrupt lock
     | *Note POSIX Safety Concepts::.

     The ‘putchar’ function is equivalent to ‘putc’ with ‘stdout’ as the
     value of the STREAM argument.

 -- Function: wint_t putwchar (wchar_t WC)
     Preliminary: | MT-Safe | AS-Unsafe corrupt | AC-Unsafe corrupt lock
     | *Note POSIX Safety Concepts::.

     The ‘putwchar’ function is equivalent to ‘putwc’ with ‘stdout’ as
     the value of the STREAM argument.

 -- Function: int putchar_unlocked (int C)
     Preliminary: | MT-Unsafe race:stdout | AS-Unsafe corrupt |
     AC-Unsafe corrupt | *Note POSIX Safety Concepts::.

     The ‘putchar_unlocked’ function is equivalent to the ‘putchar’
     function except that it does not implicitly lock the stream.

 -- Function: wint_t putwchar_unlocked (wchar_t WC)
     Preliminary: | MT-Unsafe race:stdout | AS-Unsafe corrupt |
     AC-Unsafe corrupt | *Note POSIX Safety Concepts::.

     The ‘putwchar_unlocked’ function is equivalent to the ‘putwchar’
     function except that it does not implicitly lock the stream.

     This function is a GNU extension.

 -- Function: int fputs (const char *S, FILE *STREAM)
     Preliminary: | MT-Safe | AS-Unsafe corrupt | AC-Unsafe corrupt lock
     | *Note POSIX Safety Concepts::.

     The function ‘fputs’ writes the string S to the stream STREAM.  The
     terminating null character is not written.  This function does
     _not_ add a newline character, either.  It outputs only the
     characters in the string.

     This function returns ‘EOF’ if a write error occurs, and otherwise
     a non-negative value.

     For example:

          fputs ("Are ", stdout);
          fputs ("you ", stdout);
          fputs ("hungry?\n", stdout);

     outputs the text ‘Are you hungry?’ followed by a newline.

 -- Function: int fputws (const wchar_t *WS, FILE *STREAM)
     Preliminary: | MT-Safe | AS-Unsafe corrupt | AC-Unsafe corrupt lock
     | *Note POSIX Safety Concepts::.

     The function ‘fputws’ writes the wide character string WS to the
     stream STREAM.  The terminating null character is not written.
     This function does _not_ add a newline character, either.  It
     outputs only the characters in the string.

     This function returns ‘WEOF’ if a write error occurs, and otherwise
     a non-negative value.

 -- Function: int fputs_unlocked (const char *S, FILE *STREAM)
     Preliminary: | MT-Safe race:stream | AS-Unsafe corrupt | AC-Unsafe
     corrupt | *Note POSIX Safety Concepts::.

     The ‘fputs_unlocked’ function is equivalent to the ‘fputs’ function
     except that it does not implicitly lock the stream.

     This function is a GNU extension.

 -- Function: int fputws_unlocked (const wchar_t *WS, FILE *STREAM)
     Preliminary: | MT-Safe race:stream | AS-Unsafe corrupt | AC-Unsafe
     corrupt | *Note POSIX Safety Concepts::.

     The ‘fputws_unlocked’ function is equivalent to the ‘fputws’
     function except that it does not implicitly lock the stream.

     This function is a GNU extension.

 -- Function: int puts (const char *S)
     Preliminary: | MT-Safe | AS-Unsafe corrupt | AC-Unsafe lock corrupt
     | *Note POSIX Safety Concepts::.

     The ‘puts’ function writes the string S to the stream ‘stdout’
     followed by a newline.  The terminating null character of the
     string is not written.  (Note that ‘fputs’ does _not_ write a
     newline as this function does.)

     ‘puts’ is the most convenient function for printing simple
     messages.  For example:

          puts ("This is a message.");

     outputs the text ‘This is a message.’ followed by a newline.

 -- Function: int putw (int W, FILE *STREAM)
     Preliminary: | MT-Safe | AS-Unsafe corrupt | AC-Unsafe lock corrupt
     | *Note POSIX Safety Concepts::.

     This function writes the word W (that is, an ‘int’) to STREAM.  It
     is provided for compatibility with SVID, but we recommend you use
     ‘fwrite’ instead (*note Block Input/Output::).


File: libc.info,  Node: Character Input,  Next: Line Input,  Prev: Simple Output,  Up: I/O on Streams

12.8 Character Input
====================

This section describes functions for performing character-oriented
input.  These narrow stream functions are declared in the header file
‘stdio.h’ and the wide character functions are declared in ‘wchar.h’.

   These functions return an ‘int’ or ‘wint_t’ value (for narrow and
wide stream functions respectively) that is either a character of input,
or the special value ‘EOF’/‘WEOF’ (usually -1).  For the narrow stream
functions it is important to store the result of these functions in a
variable of type ‘int’ instead of ‘char’, even when you plan to use it
only as a character.  Storing ‘EOF’ in a ‘char’ variable truncates its
value to the size of a character, so that it is no longer
distinguishable from the valid character ‘(char) -1’.  So always use an
‘int’ for the result of ‘getc’ and friends, and check for ‘EOF’ after
the call; once you’ve verified that the result is not ‘EOF’, you can be
sure that it will fit in a ‘char’ variable without loss of information.

 -- Function: int fgetc (FILE *STREAM)
     Preliminary: | MT-Safe | AS-Unsafe corrupt | AC-Unsafe lock corrupt
     | *Note POSIX Safety Concepts::.

     This function reads the next character as an ‘unsigned char’ from
     the stream STREAM and returns its value, converted to an ‘int’.  If
     an end-of-file condition or read error occurs, ‘EOF’ is returned
     instead.

 -- Function: wint_t fgetwc (FILE *STREAM)
     Preliminary: | MT-Safe | AS-Unsafe corrupt | AC-Unsafe lock corrupt
     | *Note POSIX Safety Concepts::.

     This function reads the next wide character from the stream STREAM
     and returns its value.  If an end-of-file condition or read error
     occurs, ‘WEOF’ is returned instead.

 -- Function: int fgetc_unlocked (FILE *STREAM)
     Preliminary: | MT-Safe race:stream | AS-Unsafe corrupt | AC-Unsafe
     corrupt | *Note POSIX Safety Concepts::.

     The ‘fgetc_unlocked’ function is equivalent to the ‘fgetc’ function
     except that it does not implicitly lock the stream.

 -- Function: wint_t fgetwc_unlocked (FILE *STREAM)
     Preliminary: | MT-Safe race:stream | AS-Unsafe corrupt | AC-Unsafe
     corrupt | *Note POSIX Safety Concepts::.

     The ‘fgetwc_unlocked’ function is equivalent to the ‘fgetwc’
     function except that it does not implicitly lock the stream.

     This function is a GNU extension.

 -- Function: int getc (FILE *STREAM)
     Preliminary: | MT-Safe | AS-Unsafe corrupt | AC-Unsafe lock corrupt
     | *Note POSIX Safety Concepts::.

     This is just like ‘fgetc’, except that it is permissible (and
     typical) for it to be implemented as a macro that evaluates the
     STREAM argument more than once.  ‘getc’ is often highly optimized,
     so it is usually the best function to use to read a single
     character.

 -- Function: wint_t getwc (FILE *STREAM)
     Preliminary: | MT-Safe | AS-Unsafe corrupt | AC-Unsafe lock corrupt
     | *Note POSIX Safety Concepts::.

     This is just like ‘fgetwc’, except that it is permissible for it to
     be implemented as a macro that evaluates the STREAM argument more
     than once.  ‘getwc’ can be highly optimized, so it is usually the
     best function to use to read a single wide character.

 -- Function: int getc_unlocked (FILE *STREAM)
     Preliminary: | MT-Safe race:stream | AS-Unsafe corrupt | AC-Unsafe
     corrupt | *Note POSIX Safety Concepts::.

     The ‘getc_unlocked’ function is equivalent to the ‘getc’ function
     except that it does not implicitly lock the stream.

 -- Function: wint_t getwc_unlocked (FILE *STREAM)
     Preliminary: | MT-Safe race:stream | AS-Unsafe corrupt | AC-Unsafe
     corrupt | *Note POSIX Safety Concepts::.

     The ‘getwc_unlocked’ function is equivalent to the ‘getwc’ function
     except that it does not implicitly lock the stream.

     This function is a GNU extension.

 -- Function: int getchar (void)
     Preliminary: | MT-Safe | AS-Unsafe corrupt | AC-Unsafe lock corrupt
     | *Note POSIX Safety Concepts::.

     The ‘getchar’ function is equivalent to ‘getc’ with ‘stdin’ as the
     value of the STREAM argument.

 -- Function: wint_t getwchar (void)
     Preliminary: | MT-Safe | AS-Unsafe corrupt | AC-Unsafe lock corrupt
     | *Note POSIX Safety Concepts::.

     The ‘getwchar’ function is equivalent to ‘getwc’ with ‘stdin’ as
     the value of the STREAM argument.

 -- Function: int getchar_unlocked (void)
     Preliminary: | MT-Unsafe race:stdin | AS-Unsafe corrupt | AC-Unsafe
     corrupt | *Note POSIX Safety Concepts::.

     The ‘getchar_unlocked’ function is equivalent to the ‘getchar’
     function except that it does not implicitly lock the stream.

 -- Function: wint_t getwchar_unlocked (void)
     Preliminary: | MT-Unsafe race:stdin | AS-Unsafe corrupt | AC-Unsafe
     corrupt | *Note POSIX Safety Concepts::.

     The ‘getwchar_unlocked’ function is equivalent to the ‘getwchar’
     function except that it does not implicitly lock the stream.

     This function is a GNU extension.

   Here is an example of a function that does input using ‘fgetc’.  It
would work just as well using ‘getc’ instead, or using ‘getchar ()’
instead of ‘fgetc (stdin)’.  The code would also work the same for the
wide character stream functions.

     int
     y_or_n_p (const char *question)
     {
       fputs (question, stdout);
       while (1)
         {
           int c, answer;
           /* Write a space to separate answer from question. */
           fputc (' ', stdout);
           /* Read the first character of the line.
	      This should be the answer character, but might not be. */
           c = tolower (fgetc (stdin));
           answer = c;
           /* Discard rest of input line. */
           while (c != '\n' && c != EOF)
     	c = fgetc (stdin);
           /* Obey the answer if it was valid. */
           if (answer == 'y')
     	return 1;
           if (answer == 'n')
     	return 0;
           /* Answer was invalid: ask for valid answer. */
           fputs ("Please answer y or n:", stdout);
         }
     }

 -- Function: int getw (FILE *STREAM)
     Preliminary: | MT-Safe | AS-Unsafe corrupt | AC-Unsafe lock corrupt
     | *Note POSIX Safety Concepts::.

     This function reads a word (that is, an ‘int’) from STREAM.  It’s
     provided for compatibility with SVID. We recommend you use ‘fread’
     instead (*note Block Input/Output::).  Unlike ‘getc’, any ‘int’
     value could be a valid result.  ‘getw’ returns ‘EOF’ when it
     encounters end-of-file or an error, but there is no way to
     distinguish this from an input word with value -1.


File: libc.info,  Node: Line Input,  Next: Unreading,  Prev: Character Input,  Up: I/O on Streams

12.9 Line-Oriented Input
========================

Since many programs interpret input on the basis of lines, it is
convenient to have functions to read a line of text from a stream.

   Standard C has functions to do this, but they aren’t very safe: null
characters and even (for ‘gets’) long lines can confuse them.  So the
GNU C Library provides the nonstandard ‘getline’ function that makes it
easy to read lines reliably.

   Another GNU extension, ‘getdelim’, generalizes ‘getline’.  It reads a
delimited record, defined as everything through the next occurrence of a
specified delimiter character.

   All these functions are declared in ‘stdio.h’.

 -- Function: ssize_t getline (char **LINEPTR, size_t *N, FILE *STREAM)
     Preliminary: | MT-Safe | AS-Unsafe corrupt heap | AC-Unsafe lock
     corrupt mem | *Note POSIX Safety Concepts::.

     This function reads an entire line from STREAM, storing the text
     (including the newline and a terminating null character) in a
     buffer and storing the buffer address in ‘*LINEPTR’.

     Before calling ‘getline’, you should place in ‘*LINEPTR’ the
     address of a buffer ‘*N’ bytes long, allocated with ‘malloc’.  If
     this buffer is long enough to hold the line, ‘getline’ stores the
     line in this buffer.  Otherwise, ‘getline’ makes the buffer bigger
     using ‘realloc’, storing the new buffer address back in ‘*LINEPTR’
     and the increased size back in ‘*N’.  *Note Unconstrained
     Allocation::.

     If you set ‘*LINEPTR’ to a null pointer, and ‘*N’ to zero, before
     the call, then ‘getline’ allocates the initial buffer for you by
     calling ‘malloc’.  This buffer remains allocated even if ‘getline’
     encounters errors and is unable to read any bytes.

     In either case, when ‘getline’ returns, ‘*LINEPTR’ is a ‘char *’
     which points to the text of the line.

     When ‘getline’ is successful, it returns the number of characters
     read (including the newline, but not including the terminating
     null).  This value enables you to distinguish null characters that
     are part of the line from the null character inserted as a
     terminator.

     This function is a GNU extension, but it is the recommended way to
     read lines from a stream.  The alternative standard functions are
     unreliable.

     If an error occurs or end of file is reached without any bytes
     read, ‘getline’ returns ‘-1’.

 -- Function: ssize_t getdelim (char **LINEPTR, size_t *N, int
          DELIMITER, FILE *STREAM)
     Preliminary: | MT-Safe | AS-Unsafe corrupt heap | AC-Unsafe lock
     corrupt mem | *Note POSIX Safety Concepts::.

     This function is like ‘getline’ except that the character which
     tells it to stop reading is not necessarily newline.  The argument
     DELIMITER specifies the delimiter character; ‘getdelim’ keeps
     reading until it sees that character (or end of file).

     The text is stored in LINEPTR, including the delimiter character
     and a terminating null.  Like ‘getline’, ‘getdelim’ makes LINEPTR
     bigger if it isn’t big enough.

     ‘getline’ is in fact implemented in terms of ‘getdelim’, just like
     this:

          ssize_t
          getline (char **lineptr, size_t *n, FILE *stream)
          {
            return getdelim (lineptr, n, '\n', stream);
          }

 -- Function: char * fgets (char *S, int COUNT, FILE *STREAM)
     Preliminary: | MT-Safe | AS-Unsafe corrupt | AC-Unsafe lock corrupt
     | *Note POSIX Safety Concepts::.

     The ‘fgets’ function reads characters from the stream STREAM up to
     and including a newline character and stores them in the string S,
     adding a null character to mark the end of the string.  You must
     supply COUNT characters worth of space in S, but the number of
     characters read is at most COUNT − 1.  The extra character space is
     used to hold the null character at the end of the string.

     If the system is already at end of file when you call ‘fgets’, then
     the contents of the array S are unchanged and a null pointer is
     returned.  A null pointer is also returned if a read error occurs.
     Otherwise, the return value is the pointer S.

     *Warning:* If the input data has a null character, you can’t tell.
     So don’t use ‘fgets’ unless you know the data cannot contain a
     null.  Don’t use it to read files edited by the user because, if
     the user inserts a null character, you should either handle it
     properly or print a clear error message.  We recommend using
     ‘getline’ instead of ‘fgets’.

 -- Function: wchar_t * fgetws (wchar_t *WS, int COUNT, FILE *STREAM)
     Preliminary: | MT-Safe | AS-Unsafe corrupt | AC-Unsafe lock corrupt
     | *Note POSIX Safety Concepts::.

     The ‘fgetws’ function reads wide characters from the stream STREAM
     up to and including a newline character and stores them in the
     string WS, adding a null wide character to mark the end of the
     string.  You must supply COUNT wide characters worth of space in
     WS, but the number of characters read is at most COUNT − 1.  The
     extra character space is used to hold the null wide character at
     the end of the string.

     If the system is already at end of file when you call ‘fgetws’,
     then the contents of the array WS are unchanged and a null pointer
     is returned.  A null pointer is also returned if a read error
     occurs.  Otherwise, the return value is the pointer WS.

     *Warning:* If the input data has a null wide character (which are
     null bytes in the input stream), you can’t tell.  So don’t use
     ‘fgetws’ unless you know the data cannot contain a null.  Don’t use
     it to read files edited by the user because, if the user inserts a
     null character, you should either handle it properly or print a
     clear error message.

 -- Function: char * fgets_unlocked (char *S, int COUNT, FILE *STREAM)
     Preliminary: | MT-Safe race:stream | AS-Unsafe corrupt | AC-Unsafe
     corrupt | *Note POSIX Safety Concepts::.

     The ‘fgets_unlocked’ function is equivalent to the ‘fgets’ function
     except that it does not implicitly lock the stream.

     This function is a GNU extension.

 -- Function: wchar_t * fgetws_unlocked (wchar_t *WS, int COUNT, FILE
          *STREAM)
     Preliminary: | MT-Safe race:stream | AS-Unsafe corrupt | AC-Unsafe
     corrupt | *Note POSIX Safety Concepts::.

     The ‘fgetws_unlocked’ function is equivalent to the ‘fgetws’
     function except that it does not implicitly lock the stream.

     This function is a GNU extension.

 -- Deprecated function: char * gets (char *S)
     Preliminary: | MT-Safe | AS-Unsafe corrupt | AC-Unsafe lock corrupt
     | *Note POSIX Safety Concepts::.

     The function ‘gets’ reads characters from the stream ‘stdin’ up to
     the next newline character, and stores them in the string S.  The
     newline character is discarded (note that this differs from the
     behavior of ‘fgets’, which copies the newline character into the
     string).  If ‘gets’ encounters a read error or end-of-file, it
     returns a null pointer; otherwise it returns S.

     *Warning:* The ‘gets’ function is *very dangerous* because it
     provides no protection against overflowing the string S.  The GNU C
     Library includes it for compatibility only.  You should *always*
     use ‘fgets’ or ‘getline’ instead.  To remind you of this, the
     linker (if using GNU ‘ld’) will issue a warning whenever you use
     ‘gets’.


File: libc.info,  Node: Unreading,  Next: Block Input/Output,  Prev: Line Input,  Up: I/O on Streams

12.10 Unreading
===============

In parser programs it is often useful to examine the next character in
the input stream without removing it from the stream.  This is called
“peeking ahead” at the input because your program gets a glimpse of the
input it will read next.

   Using stream I/O, you can peek ahead at input by first reading it and
then "unreading" it (also called "pushing it back" on the stream).
Unreading a character makes it available to be input again from the
stream, by the next call to ‘fgetc’ or other input function on that
stream.

* Menu:

* Unreading Idea::              An explanation of unreading with pictures.
* How Unread::                  How to call ‘ungetc’ to do unreading.


File: libc.info,  Node: Unreading Idea,  Next: How Unread,  Up: Unreading

12.10.1 What Unreading Means
----------------------------

Here is a pictorial explanation of unreading.  Suppose you have a stream
reading a file that contains just six characters, the letters ‘foobar’.
Suppose you have read three characters so far.  The situation looks like
this:

     f  o  o  b  a  r
     	 ^

so the next input character will be ‘b’.

   If instead of reading ‘b’ you unread the letter ‘o’, you get a
situation like this:

     f  o  o  b  a  r
     	 |
           o--
           ^

so that the next input characters will be ‘o’ and ‘b’.

   If you unread ‘9’ instead of ‘o’, you get this situation:

     f  o  o  b  a  r
     	 |
           9--
           ^

so that the next input characters will be ‘9’ and ‘b’.


File: libc.info,  Node: How Unread,  Prev: Unreading Idea,  Up: Unreading

12.10.2 Using ‘ungetc’ To Do Unreading
--------------------------------------

The function to unread a character is called ‘ungetc’, because it
reverses the action of ‘getc’.

 -- Function: int ungetc (int C, FILE *STREAM)
     Preliminary: | MT-Safe | AS-Unsafe corrupt | AC-Unsafe lock corrupt
     | *Note POSIX Safety Concepts::.

     The ‘ungetc’ function pushes back the character C onto the input
     stream STREAM.  So the next input from STREAM will read C before
     anything else.

     If C is ‘EOF’, ‘ungetc’ does nothing and just returns ‘EOF’.  This
     lets you call ‘ungetc’ with the return value of ‘getc’ without
     needing to check for an error from ‘getc’.

     The character that you push back doesn’t have to be the same as the
     last character that was actually read from the stream.  In fact, it
     isn’t necessary to actually read any characters from the stream
     before unreading them with ‘ungetc’!  But that is a strange way to
     write a program; usually ‘ungetc’ is used only to unread a
     character that was just read from the same stream.  The GNU C
     Library supports this even on files opened in binary mode, but
     other systems might not.

     The GNU C Library only supports one character of pushback—in other
     words, it does not work to call ‘ungetc’ twice without doing input
     in between.  Other systems might let you push back multiple
     characters; then reading from the stream retrieves the characters
     in the reverse order that they were pushed.

     Pushing back characters doesn’t alter the file; only the internal
     buffering for the stream is affected.  If a file positioning
     function (such as ‘fseek’, ‘fseeko’ or ‘rewind’; *note File
     Positioning::) is called, any pending pushed-back characters are
     discarded.

     Unreading a character on a stream that is at end of file clears the
     end-of-file indicator for the stream, because it makes the
     character of input available.  After you read that character,
     trying to read again will encounter end of file.

 -- Function: wint_t ungetwc (wint_t WC, FILE *STREAM)
     Preliminary: | MT-Safe | AS-Unsafe corrupt | AC-Unsafe lock corrupt
     | *Note POSIX Safety Concepts::.

     The ‘ungetwc’ function behaves just like ‘ungetc’ just that it
     pushes back a wide character.

   Here is an example showing the use of ‘getc’ and ‘ungetc’ to skip
over whitespace characters.  When this function reaches a non-whitespace
character, it unreads that character to be seen again on the next read
operation on the stream.

     #include <stdio.h>
     #include <ctype.h>

     void
     skip_whitespace (FILE *stream)
     {
       int c;
       do
         /* No need to check for ‘EOF’ because it is not
            ‘isspace’, and ‘ungetc’ ignores ‘EOF’.  */
         c = getc (stream);
       while (isspace (c));
       ungetc (c, stream);
     }


File: libc.info,  Node: Block Input/Output,  Next: Formatted Output,  Prev: Unreading,  Up: I/O on Streams

12.11 Block Input/Output
========================

This section describes how to do input and output operations on blocks
of data.  You can use these functions to read and write binary data, as
well as to read and write text in fixed-size blocks instead of by
characters or lines.

   Binary files are typically used to read and write blocks of data in
the same format as is used to represent the data in a running program.
In other words, arbitrary blocks of memory—not just character or string
objects—can be written to a binary file, and meaningfully read in again
by the same program.

   Storing data in binary form is often considerably more efficient than
using the formatted I/O functions.  Also, for floating-point numbers,
the binary form avoids possible loss of precision in the conversion
process.  On the other hand, binary files can’t be examined or modified
easily using many standard file utilities (such as text editors), and
are not portable between different implementations of the language, or
different kinds of computers.

   These functions are declared in ‘stdio.h’.

 -- Function: size_t fread (void *DATA, size_t SIZE, size_t COUNT, FILE
          *STREAM)
     Preliminary: | MT-Safe | AS-Unsafe corrupt | AC-Unsafe lock corrupt
     | *Note POSIX Safety Concepts::.

     This function reads up to COUNT objects of size SIZE into the array
     DATA, from the stream STREAM.  It returns the number of objects
     actually read, which might be less than COUNT if a read error
     occurs or the end of the file is reached.  This function returns a
     value of zero (and doesn’t read anything) if either SIZE or COUNT
     is zero.

     If ‘fread’ encounters end of file in the middle of an object, it
     returns the number of complete objects read, and discards the
     partial object.  Therefore, the stream remains at the actual end of
     the file.

 -- Function: size_t fread_unlocked (void *DATA, size_t SIZE, size_t
          COUNT, FILE *STREAM)
     Preliminary: | MT-Safe race:stream | AS-Unsafe corrupt | AC-Unsafe
     corrupt | *Note POSIX Safety Concepts::.

     The ‘fread_unlocked’ function is equivalent to the ‘fread’ function
     except that it does not implicitly lock the stream.

     This function is a GNU extension.

 -- Function: size_t fwrite (const void *DATA, size_t SIZE, size_t
          COUNT, FILE *STREAM)
     Preliminary: | MT-Safe | AS-Unsafe corrupt | AC-Unsafe lock corrupt
     | *Note POSIX Safety Concepts::.

     This function writes up to COUNT objects of size SIZE from the
     array DATA, to the stream STREAM.  The return value is normally
     COUNT, if the call succeeds.  Any other value indicates some sort
     of error, such as running out of space.

 -- Function: size_t fwrite_unlocked (const void *DATA, size_t SIZE,
          size_t COUNT, FILE *STREAM)
     Preliminary: | MT-Safe race:stream | AS-Unsafe corrupt | AC-Unsafe
     corrupt | *Note POSIX Safety Concepts::.

     The ‘fwrite_unlocked’ function is equivalent to the ‘fwrite’
     function except that it does not implicitly lock the stream.

     This function is a GNU extension.


File: libc.info,  Node: Formatted Output,  Next: Customizing Printf,  Prev: Block Input/Output,  Up: I/O on Streams

12.12 Formatted Output
======================

The functions described in this section (‘printf’ and related functions)
provide a convenient way to perform formatted output.  You call ‘printf’
with a "format string" or "template string" that specifies how to format
the values of the remaining arguments.

   Unless your program is a filter that specifically performs line- or
character-oriented processing, using ‘printf’ or one of the other
related functions described in this section is usually the easiest and
most concise way to perform output.  These functions are especially
useful for printing error messages, tables of data, and the like.

* Menu:

* Formatted Output Basics::     Some examples to get you started.
* Output Conversion Syntax::    General syntax of conversion
				 specifications.
* Table of Output Conversions:: Summary of output conversions and
				 what they do.
* Integer Conversions::         Details about formatting of integers.
* Floating-Point Conversions::  Details about formatting of
				 floating-point numbers.
* Other Output Conversions::    Details about formatting of strings,
				 characters, pointers, and the like.
* Formatted Output Functions::  Descriptions of the actual functions.
* Dynamic Output::		Functions that allocate memory for the output.
* Variable Arguments Output::   ‘vprintf’ and friends.
* Parsing a Template String::   What kinds of args does a given template
				 call for?
* Example of Parsing::          Sample program using ‘parse_printf_format’.


File: libc.info,  Node: Formatted Output Basics,  Next: Output Conversion Syntax,  Up: Formatted Output

12.12.1 Formatted Output Basics
-------------------------------

The ‘printf’ function can be used to print any number of arguments.  The
template string argument you supply in a call provides information not
only about the number of additional arguments, but also about their
types and what style should be used for printing them.

   Ordinary characters in the template string are simply written to the
output stream as-is, while "conversion specifications" introduced by a
‘%’ character in the template cause subsequent arguments to be formatted
and written to the output stream.  For example,

     int pct = 37;
     char filename[] = "foo.txt";
     printf ("Processing of `%s' is %d%% finished.\nPlease be patient.\n",
     	filename, pct);

produces output like

     Processing of `foo.txt' is 37% finished.
     Please be patient.

   This example shows the use of the ‘%d’ conversion to specify that an
‘int’ argument should be printed in decimal notation, the ‘%s’
conversion to specify printing of a string argument, and the ‘%%’
conversion to print a literal ‘%’ character.

   There are also conversions for printing an integer argument as an
unsigned value in octal, decimal, or hexadecimal radix (‘%o’, ‘%u’, or
‘%x’, respectively); or as a character value (‘%c’).

   Floating-point numbers can be printed in normal, fixed-point notation
using the ‘%f’ conversion or in exponential notation using the ‘%e’
conversion.  The ‘%g’ conversion uses either ‘%e’ or ‘%f’ format,
depending on what is more appropriate for the magnitude of the
particular number.

   You can control formatting more precisely by writing "modifiers"
between the ‘%’ and the character that indicates which conversion to
apply.  These slightly alter the ordinary behavior of the conversion.
For example, most conversion specifications permit you to specify a
minimum field width and a flag indicating whether you want the result
left- or right-justified within the field.

   The specific flags and modifiers that are permitted and their
interpretation vary depending on the particular conversion.  They’re all
described in more detail in the following sections.  Don’t worry if this
all seems excessively complicated at first; you can almost always get
reasonable free-format output without using any of the modifiers at all.
The modifiers are mostly used to make the output look “prettier” in
tables.


File: libc.info,  Node: Output Conversion Syntax,  Next: Table of Output Conversions,  Prev: Formatted Output Basics,  Up: Formatted Output

12.12.2 Output Conversion Syntax
--------------------------------

This section provides details about the precise syntax of conversion
specifications that can appear in a ‘printf’ template string.

   Characters in the template string that are not part of a conversion
specification are printed as-is to the output stream.  Multibyte
character sequences (*note Character Set Handling::) are permitted in a
template string.

   The conversion specifications in a ‘printf’ template string have the
general form:

     % [ PARAM-NO $] FLAGS WIDTH [ . PRECISION ] TYPE CONVERSION

or

     % [ PARAM-NO $] FLAGS WIDTH . * [ PARAM-NO $] TYPE CONVERSION

   For example, in the conversion specifier ‘%-10.8ld’, the ‘-’ is a
flag, ‘10’ specifies the field width, the precision is ‘8’, the letter
‘l’ is a type modifier, and ‘d’ specifies the conversion style.  (This
particular type specifier says to print a ‘long int’ argument in decimal
notation, with a minimum of 8 digits left-justified in a field at least
10 characters wide.)

   In more detail, output conversion specifications consist of an
initial ‘%’ character followed in sequence by:

   • An optional specification of the parameter used for this format.
     Normally the parameters to the ‘printf’ function are assigned to
     the formats in the order of appearance in the format string.  But
     in some situations (such as message translation) this is not
     desirable and this extension allows an explicit parameter to be
     specified.

     The PARAM-NO parts of the format must be integers in the range of 1
     to the maximum number of arguments present to the function call.
     Some implementations limit this number to a certain upper bound.
     The exact limit can be retrieved by the following constant.

      -- Macro: NL_ARGMAX
          The value of ‘NL_ARGMAX’ is the maximum value allowed for the
          specification of a positional parameter in a ‘printf’ call.
          The actual value in effect at runtime can be retrieved by
          using ‘sysconf’ using the ‘_SC_NL_ARGMAX’ parameter *note
          Sysconf Definition::.

          Some systems have a quite low limit such as 9 for System V
          systems.  The GNU C Library has no real limit.

     If any of the formats has a specification for the parameter
     position all of them in the format string shall have one.
     Otherwise the behavior is undefined.

   • Zero or more "flag characters" that modify the normal behavior of
     the conversion specification.

   • An optional decimal integer specifying the "minimum field width".
     If the normal conversion produces fewer characters than this, the
     field is padded with spaces to the specified width.  This is a
     _minimum_ value; if the normal conversion produces more characters
     than this, the field is _not_ truncated.  Normally, the output is
     right-justified within the field.

     You can also specify a field width of ‘*’.  This means that the
     next argument in the argument list (before the actual value to be
     printed) is used as the field width.  The value must be an ‘int’.
     If the value is negative, this means to set the ‘-’ flag (see
     below) and to use the absolute value as the field width.

   • An optional "precision" to specify the number of digits to be
     written for the numeric conversions.  If the precision is
     specified, it consists of a period (‘.’) followed optionally by a
     decimal integer (which defaults to zero if omitted).

     You can also specify a precision of ‘*’.  This means that the next
     argument in the argument list (before the actual value to be
     printed) is used as the precision.  The value must be an ‘int’, and
     is ignored if it is negative.  If you specify ‘*’ for both the
     field width and precision, the field width argument precedes the
     precision argument.  Other C library versions may not recognize
     this syntax.

   • An optional "type modifier character", which is used to specify the
     data type of the corresponding argument if it differs from the
     default type.  (For example, the integer conversions assume a type
     of ‘int’, but you can specify ‘h’, ‘l’, or ‘L’ for other integer
     types.)

   • A character that specifies the conversion to be applied.

   The exact options that are permitted and how they are interpreted
vary between the different conversion specifiers.  See the descriptions
of the individual conversions for information about the particular
options that they use.

   With the ‘-Wformat’ option, the GNU C compiler checks calls to
‘printf’ and related functions.  It examines the format string and
verifies that the correct number and types of arguments are supplied.
There is also a GNU C syntax to tell the compiler that a function you
write uses a ‘printf’-style format string.  *Note Declaring Attributes
of Functions: (gcc.info)Function Attributes, for more information.


File: libc.info,  Node: Table of Output Conversions,  Next: Integer Conversions,  Prev: Output Conversion Syntax,  Up: Formatted Output

12.12.3 Table of Output Conversions
-----------------------------------

Here is a table summarizing what all the different conversions do:

‘%d’, ‘%i’
     Print an integer as a signed decimal number.  *Note Integer
     Conversions::, for details.  ‘%d’ and ‘%i’ are synonymous for
     output, but are different when used with ‘scanf’ for input (*note
     Table of Input Conversions::).

‘%o’
     Print an integer as an unsigned octal number.  *Note Integer
     Conversions::, for details.

‘%u’
     Print an integer as an unsigned decimal number.  *Note Integer
     Conversions::, for details.

‘%x’, ‘%X’
     Print an integer as an unsigned hexadecimal number.  ‘%x’ uses
     lower-case letters and ‘%X’ uses upper-case.  *Note Integer
     Conversions::, for details.

‘%f’
     Print a floating-point number in normal (fixed-point) notation.
     *Note Floating-Point Conversions::, for details.

‘%e’, ‘%E’
     Print a floating-point number in exponential notation.  ‘%e’ uses
     lower-case letters and ‘%E’ uses upper-case.  *Note Floating-Point
     Conversions::, for details.

‘%g’, ‘%G’
     Print a floating-point number in either normal or exponential
     notation, whichever is more appropriate for its magnitude.  ‘%g’
     uses lower-case letters and ‘%G’ uses upper-case.  *Note
     Floating-Point Conversions::, for details.

‘%a’, ‘%A’
     Print a floating-point number in a hexadecimal fractional notation
     with the exponent to base 2 represented in decimal digits.  ‘%a’
     uses lower-case letters and ‘%A’ uses upper-case.  *Note
     Floating-Point Conversions::, for details.

‘%c’
     Print a single character.  *Note Other Output Conversions::.

‘%C’
     This is an alias for ‘%lc’ which is supported for compatibility
     with the Unix standard.

‘%s’
     Print a string.  *Note Other Output Conversions::.

‘%S’
     This is an alias for ‘%ls’ which is supported for compatibility
     with the Unix standard.

‘%p’
     Print the value of a pointer.  *Note Other Output Conversions::.

‘%n’
     Get the number of characters printed so far.  *Note Other Output
     Conversions::.  Note that this conversion specification never
     produces any output.

‘%m’
     Print the string corresponding to the value of ‘errno’.  (This is a
     GNU extension.)  *Note Other Output Conversions::.

‘%%’
     Print a literal ‘%’ character.  *Note Other Output Conversions::.

   If the syntax of a conversion specification is invalid, unpredictable
things will happen, so don’t do this.  If there aren’t enough function
arguments provided to supply values for all the conversion
specifications in the template string, or if the arguments are not of
the correct types, the results are unpredictable.  If you supply more
arguments than conversion specifications, the extra argument values are
simply ignored; this is sometimes useful.


File: libc.info,  Node: Integer Conversions,  Next: Floating-Point Conversions,  Prev: Table of Output Conversions,  Up: Formatted Output

12.12.4 Integer Conversions
---------------------------

This section describes the options for the ‘%d’, ‘%i’, ‘%o’, ‘%u’, ‘%x’,
and ‘%X’ conversion specifications.  These conversions print integers in
various formats.

   The ‘%d’ and ‘%i’ conversion specifications both print an ‘int’
argument as a signed decimal number; while ‘%o’, ‘%u’, and ‘%x’ print
the argument as an unsigned octal, decimal, or hexadecimal number
(respectively).  The ‘%X’ conversion specification is just like ‘%x’
except that it uses the characters ‘ABCDEF’ as digits instead of
‘abcdef’.

   The following flags are meaningful:

‘-’
     Left-justify the result in the field (instead of the normal
     right-justification).

‘+’
     For the signed ‘%d’ and ‘%i’ conversions, print a plus sign if the
     value is positive.

‘ ’
     For the signed ‘%d’ and ‘%i’ conversions, if the result doesn’t
     start with a plus or minus sign, prefix it with a space character
     instead.  Since the ‘+’ flag ensures that the result includes a
     sign, this flag is ignored if you supply both of them.

‘#’
     For the ‘%o’ conversion, this forces the leading digit to be ‘0’,
     as if by increasing the precision.  For ‘%x’ or ‘%X’, this prefixes
     a leading ‘0x’ or ‘0X’ (respectively) to the result.  This doesn’t
     do anything useful for the ‘%d’, ‘%i’, or ‘%u’ conversions.  Using
     this flag produces output which can be parsed by the ‘strtoul’
     function (*note Parsing of Integers::) and ‘scanf’ with the ‘%i’
     conversion (*note Numeric Input Conversions::).

‘'’
     Separate the digits into groups as specified by the locale
     specified for the ‘LC_NUMERIC’ category; *note General Numeric::.
     This flag is a GNU extension.

‘0’
     Pad the field with zeros instead of spaces.  The zeros are placed
     after any indication of sign or base.  This flag is ignored if the
     ‘-’ flag is also specified, or if a precision is specified.

   If a precision is supplied, it specifies the minimum number of digits
to appear; leading zeros are produced if necessary.  If you don’t
specify a precision, the number is printed with as many digits as it
needs.  If you convert a value of zero with an explicit precision of
zero, then no characters at all are produced.

   Without a type modifier, the corresponding argument is treated as an
‘int’ (for the signed conversions ‘%i’ and ‘%d’) or ‘unsigned int’ (for
the unsigned conversions ‘%o’, ‘%u’, ‘%x’, and ‘%X’).  Recall that since
‘printf’ and friends are variadic, any ‘char’ and ‘short’ arguments are
automatically converted to ‘int’ by the default argument promotions.
For arguments of other integer types, you can use these modifiers:

‘hh’
     Specifies that the argument is a ‘signed char’ or ‘unsigned char’,
     as appropriate.  A ‘char’ argument is converted to an ‘int’ or
     ‘unsigned int’ by the default argument promotions anyway, but the
     ‘hh’ modifier says to convert it back to a ‘char’ again.

     This modifier was introduced in ISO C99.

‘h’
     Specifies that the argument is a ‘short int’ or ‘unsigned short
     int’, as appropriate.  A ‘short’ argument is converted to an ‘int’
     or ‘unsigned int’ by the default argument promotions anyway, but
     the ‘h’ modifier says to convert it back to a ‘short’ again.

‘j’
     Specifies that the argument is a ‘intmax_t’ or ‘uintmax_t’, as
     appropriate.

     This modifier was introduced in ISO C99.

‘l’
     Specifies that the argument is a ‘long int’ or ‘unsigned long int’,
     as appropriate.  Two ‘l’ characters are like the ‘L’ modifier,
     below.

     If used with ‘%c’ or ‘%s’ the corresponding parameter is considered
     as a wide character or wide character string respectively.  This
     use of ‘l’ was introduced in Amendment 1 to ISO C90.

‘L’
‘ll’
‘q’
     Specifies that the argument is a ‘long long int’.  (This type is an
     extension supported by the GNU C compiler.  On systems that don’t
     support extra-long integers, this is the same as ‘long int’.)

     The ‘q’ modifier is another name for the same thing, which comes
     from 4.4 BSD; a ‘long long int’ is sometimes called a “quad” ‘int’.

‘t’
     Specifies that the argument is a ‘ptrdiff_t’.

     This modifier was introduced in ISO C99.

‘z’
‘Z’
     Specifies that the argument is a ‘size_t’.

     ‘z’ was introduced in ISO C99.  ‘Z’ is a GNU extension predating
     this addition and should not be used in new code.

   Here is an example.  Using the template string:

     "|%5d|%-5d|%+5d|%+-5d|% 5d|%05d|%5.0d|%5.2d|%d|\n"

to print numbers using the different options for the ‘%d’ conversion
gives results like:

     |    0|0    |   +0|+0   |    0|00000|     |   00|0|
     |    1|1    |   +1|+1   |    1|00001|    1|   01|1|
     |   -1|-1   |   -1|-1   |   -1|-0001|   -1|  -01|-1|
     |100000|100000|+100000|+100000| 100000|100000|100000|100000|100000|

   In particular, notice what happens in the last case where the number
is too large to fit in the minimum field width specified.

   Here are some more examples showing how unsigned integers print under
various format options, using the template string:

     "|%5u|%5o|%5x|%5X|%#5o|%#5x|%#5X|%#10.8x|\n"

     |    0|    0|    0|    0|    0|    0|    0|  00000000|
     |    1|    1|    1|    1|   01|  0x1|  0X1|0x00000001|
     |100000|303240|186a0|186A0|0303240|0x186a0|0X186A0|0x000186a0|


File: libc.info,  Node: Floating-Point Conversions,  Next: Other Output Conversions,  Prev: Integer Conversions,  Up: Formatted Output

12.12.5 Floating-Point Conversions
----------------------------------

This section discusses the conversion specifications for floating-point
numbers: the ‘%f’, ‘%e’, ‘%E’, ‘%g’, and ‘%G’ conversions.

   The ‘%f’ conversion prints its argument in fixed-point notation,
producing output of the form [‘-’]DDD‘.’DDD, where the number of digits
following the decimal point is controlled by the precision you specify.

   The ‘%e’ conversion prints its argument in exponential notation,
producing output of the form [‘-’]D‘.’DDD‘e’[‘+’|‘-’]DD.  Again, the
number of digits following the decimal point is controlled by the
precision.  The exponent always contains at least two digits.  The ‘%E’
conversion is similar but the exponent is marked with the letter ‘E’
instead of ‘e’.

   The ‘%g’ and ‘%G’ conversions print the argument in the style of ‘%e’
or ‘%E’ (respectively) if the exponent would be less than -4 or greater
than or equal to the precision; otherwise they use the ‘%f’ style.  A
precision of ‘0’, is taken as 1.  Trailing zeros are removed from the
fractional portion of the result and a decimal-point character appears
only if it is followed by a digit.

   The ‘%a’ and ‘%A’ conversions are meant for representing
floating-point numbers exactly in textual form so that they can be
exchanged as texts between different programs and/or machines.  The
numbers are represented in the form [‘-’]‘0x’H‘.’HHH‘p’[‘+’|‘-’]DD.  At
the left of the decimal-point character exactly one digit is print.
This character is only ‘0’ if the number is denormalized.  Otherwise the
value is unspecified; it is implementation dependent how many bits are
used.  The number of hexadecimal digits on the right side of the
decimal-point character is equal to the precision.  If the precision is
zero it is determined to be large enough to provide an exact
representation of the number (or it is large enough to distinguish two
adjacent values if the ‘FLT_RADIX’ is not a power of 2, *note Floating
Point Parameters::).  For the ‘%a’ conversion lower-case characters are
used to represent the hexadecimal number and the prefix and exponent
sign are printed as ‘0x’ and ‘p’ respectively.  Otherwise upper-case
characters are used and ‘0X’ and ‘P’ are used for the representation of
prefix and exponent string.  The exponent to the base of two is printed
as a decimal number using at least one digit but at most as many digits
as necessary to represent the value exactly.

   If the value to be printed represents infinity or a NaN, the output
is [‘-’]‘inf’ or ‘nan’ respectively if the conversion specifier is ‘%a’,
‘%e’, ‘%f’, or ‘%g’ and it is [‘-’]‘INF’ or ‘NAN’ respectively if the
conversion is ‘%A’, ‘%E’, or ‘%G’.

   The following flags can be used to modify the behavior:

‘-’
     Left-justify the result in the field.  Normally the result is
     right-justified.

‘+’
     Always include a plus or minus sign in the result.

‘ ’
     If the result doesn’t start with a plus or minus sign, prefix it
     with a space instead.  Since the ‘+’ flag ensures that the result
     includes a sign, this flag is ignored if you supply both of them.

‘#’
     Specifies that the result should always include a decimal point,
     even if no digits follow it.  For the ‘%g’ and ‘%G’ conversions,
     this also forces trailing zeros after the decimal point to be left
     in place where they would otherwise be removed.

‘'’
     Separate the digits of the integer part of the result into groups
     as specified by the locale specified for the ‘LC_NUMERIC’ category;
     *note General Numeric::.  This flag is a GNU extension.

‘0’
     Pad the field with zeros instead of spaces; the zeros are placed
     after any sign.  This flag is ignored if the ‘-’ flag is also
     specified.

   The precision specifies how many digits follow the decimal-point
character for the ‘%f’, ‘%e’, and ‘%E’ conversions.  For these
conversions, the default precision is ‘6’.  If the precision is
explicitly ‘0’, this suppresses the decimal point character entirely.
For the ‘%g’ and ‘%G’ conversions, the precision specifies how many
significant digits to print.  Significant digits are the first digit
before the decimal point, and all the digits after it.  If the precision
is ‘0’ or not specified for ‘%g’ or ‘%G’, it is treated like a value of
‘1’.  If the value being printed cannot be expressed accurately in the
specified number of digits, the value is rounded to the nearest number
that fits.

   Without a type modifier, the floating-point conversions use an
argument of type ‘double’.  (By the default argument promotions, any
‘float’ arguments are automatically converted to ‘double’.)  The
following type modifier is supported:

‘L’
     An uppercase ‘L’ specifies that the argument is a ‘long double’.

   Here are some examples showing how numbers print using the various
floating-point conversions.  All of the numbers were printed using this
template string:

     "|%13.4a|%13.4f|%13.4e|%13.4g|\n"

   Here is the output:

     |  0x0.0000p+0|       0.0000|   0.0000e+00|            0|
     |  0x1.0000p-1|       0.5000|   5.0000e-01|          0.5|
     |  0x1.0000p+0|       1.0000|   1.0000e+00|            1|
     | -0x1.0000p+0|      -1.0000|  -1.0000e+00|           -1|
     |  0x1.9000p+6|     100.0000|   1.0000e+02|          100|
     |  0x1.f400p+9|    1000.0000|   1.0000e+03|         1000|
     | 0x1.3880p+13|   10000.0000|   1.0000e+04|        1e+04|
     | 0x1.81c8p+13|   12345.0000|   1.2345e+04|    1.234e+04|
     | 0x1.86a0p+16|  100000.0000|   1.0000e+05|        1e+05|
     | 0x1.e240p+16|  123456.0000|   1.2346e+05|    1.235e+05|

   Notice how the ‘%g’ conversion drops trailing zeros.


File: libc.info,  Node: Other Output Conversions,  Next: Formatted Output Functions,  Prev: Floating-Point Conversions,  Up: Formatted Output

12.12.6 Other Output Conversions
--------------------------------

This section describes miscellaneous conversions for ‘printf’.

   The ‘%c’ conversion prints a single character.  In case there is no
‘l’ modifier the ‘int’ argument is first converted to an ‘unsigned
char’.  Then, if used in a wide stream function, the character is
converted into the corresponding wide character.  The ‘-’ flag can be
used to specify left-justification in the field, but no other flags are
defined, and no precision or type modifier can be given.  For example:

     printf ("%c%c%c%c%c", 'h', 'e', 'l', 'l', 'o');

prints ‘hello’.

   If there is an ‘l’ modifier present the argument is expected to be of
type ‘wint_t’.  If used in a multibyte function the wide character is
converted into a multibyte character before being added to the output.
In this case more than one output byte can be produced.

   The ‘%s’ conversion prints a string.  If no ‘l’ modifier is present
the corresponding argument must be of type ‘char *’ (or ‘const char *’).
If used in a wide stream function the string is first converted to a
wide character string.  A precision can be specified to indicate the
maximum number of characters to write; otherwise characters in the
string up to but not including the terminating null character are
written to the output stream.  The ‘-’ flag can be used to specify
left-justification in the field, but no other flags or type modifiers
are defined for this conversion.  For example:

     printf ("%3s%-6s", "no", "where");

prints ‘ nowhere ’.

   If there is an ‘l’ modifier present, the argument is expected to be
of type ‘wchar_t’ (or ‘const wchar_t *’).

   If you accidentally pass a null pointer as the argument for a ‘%s’
conversion, the GNU C Library prints it as ‘(null)’.  We think this is
more useful than crashing.  But it’s not good practice to pass a null
argument intentionally.

   The ‘%m’ conversion prints the string corresponding to the error code
in ‘errno’.  *Note Error Messages::.  Thus:

     fprintf (stderr, "can't open `%s': %m\n", filename);

is equivalent to:

     fprintf (stderr, "can't open `%s': %s\n", filename, strerror (errno));

The ‘%m’ conversion is a GNU C Library extension.

   The ‘%p’ conversion prints a pointer value.  The corresponding
argument must be of type ‘void *’.  In practice, you can use any type of
pointer.

   In the GNU C Library, non-null pointers are printed as unsigned
integers, as if a ‘%#x’ conversion were used.  Null pointers print as
‘(nil)’.  (Pointers might print differently in other systems.)

   For example:

     printf ("%p", "testing");

prints ‘0x’ followed by a hexadecimal number—the address of the string
constant ‘"testing"’.  It does not print the word ‘testing’.

   You can supply the ‘-’ flag with the ‘%p’ conversion to specify
left-justification, but no other flags, precision, or type modifiers are
defined.

   The ‘%n’ conversion is unlike any of the other output conversions.
It uses an argument which must be a pointer to an ‘int’, but instead of
printing anything it stores the number of characters printed so far by
this call at that location.  The ‘h’ and ‘l’ type modifiers are
permitted to specify that the argument is of type ‘short int *’ or ‘long
int *’ instead of ‘int *’, but no flags, field width, or precision are
permitted.

   For example,

     int nchar;
     printf ("%d %s%n\n", 3, "bears", &nchar);

prints:

     3 bears

and sets ‘nchar’ to ‘7’, because ‘3 bears’ is seven characters.

   The ‘%%’ conversion prints a literal ‘%’ character.  This conversion
doesn’t use an argument, and no flags, field width, precision, or type
modifiers are permitted.


File: libc.info,  Node: Formatted Output Functions,  Next: Dynamic Output,  Prev: Other Output Conversions,  Up: Formatted Output

12.12.7 Formatted Output Functions
----------------------------------

This section describes how to call ‘printf’ and related functions.
Prototypes for these functions are in the header file ‘stdio.h’.
Because these functions take a variable number of arguments, you _must_
declare prototypes for them before using them.  Of course, the easiest
way to make sure you have all the right prototypes is to just include
‘stdio.h’.

 -- Function: int printf (const char *TEMPLATE, …)
     Preliminary: | MT-Safe locale | AS-Unsafe corrupt heap | AC-Unsafe
     mem lock corrupt | *Note POSIX Safety Concepts::.

     The ‘printf’ function prints the optional arguments under the
     control of the template string TEMPLATE to the stream ‘stdout’.  It
     returns the number of characters printed, or a negative value if
     there was an output error.

 -- Function: int wprintf (const wchar_t *TEMPLATE, …)
     Preliminary: | MT-Safe locale | AS-Unsafe corrupt heap | AC-Unsafe
     mem lock corrupt | *Note POSIX Safety Concepts::.

     The ‘wprintf’ function prints the optional arguments under the
     control of the wide template string TEMPLATE to the stream
     ‘stdout’.  It returns the number of wide characters printed, or a
     negative value if there was an output error.

 -- Function: int fprintf (FILE *STREAM, const char *TEMPLATE, …)
     Preliminary: | MT-Safe locale | AS-Unsafe corrupt heap | AC-Unsafe
     mem lock corrupt | *Note POSIX Safety Concepts::.

     This function is just like ‘printf’, except that the output is
     written to the stream STREAM instead of ‘stdout’.

 -- Function: int fwprintf (FILE *STREAM, const wchar_t *TEMPLATE, …)
     Preliminary: | MT-Safe locale | AS-Unsafe corrupt heap | AC-Unsafe
     mem lock corrupt | *Note POSIX Safety Concepts::.

     This function is just like ‘wprintf’, except that the output is
     written to the stream STREAM instead of ‘stdout’.

 -- Function: int sprintf (char *S, const char *TEMPLATE, …)
     Preliminary: | MT-Safe locale | AS-Unsafe heap | AC-Unsafe mem |
     *Note POSIX Safety Concepts::.

     This is like ‘printf’, except that the output is stored in the
     character array S instead of written to a stream.  A null character
     is written to mark the end of the string.

     The ‘sprintf’ function returns the number of characters stored in
     the array S, not including the terminating null character.

     The behavior of this function is undefined if copying takes place
     between objects that overlap—for example, if S is also given as an
     argument to be printed under control of the ‘%s’ conversion.  *Note
     Copying Strings and Arrays::.

     *Warning:* The ‘sprintf’ function can be *dangerous* because it can
     potentially output more characters than can fit in the allocation
     size of the string S.  Remember that the field width given in a
     conversion specification is only a _minimum_ value.

     To avoid this problem, you can use ‘snprintf’ or ‘asprintf’,
     described below.

 -- Function: int swprintf (wchar_t *WS, size_t SIZE, const wchar_t
          *TEMPLATE, …)
     Preliminary: | MT-Safe locale | AS-Unsafe heap | AC-Unsafe mem |
     *Note POSIX Safety Concepts::.

     This is like ‘wprintf’, except that the output is stored in the
     wide character array WS instead of written to a stream.  A null
     wide character is written to mark the end of the string.  The SIZE
     argument specifies the maximum number of characters to produce.
     The trailing null character is counted towards this limit, so you
     should allocate at least SIZE wide characters for the string WS.

     The return value is the number of characters generated for the
     given input, excluding the trailing null.  If not all output fits
     into the provided buffer a negative value is returned.  You should
     try again with a bigger output string.  _Note:_ this is different
     from how ‘snprintf’ handles this situation.

     Note that the corresponding narrow stream function takes fewer
     parameters.  ‘swprintf’ in fact corresponds to the ‘snprintf’
     function.  Since the ‘sprintf’ function can be dangerous and should
     be avoided the ISO C committee refused to make the same mistake
     again and decided to not define a function exactly corresponding to
     ‘sprintf’.

 -- Function: int snprintf (char *S, size_t SIZE, const char *TEMPLATE,
          …)
     Preliminary: | MT-Safe locale | AS-Unsafe heap | AC-Unsafe mem |
     *Note POSIX Safety Concepts::.

     The ‘snprintf’ function is similar to ‘sprintf’, except that the
     SIZE argument specifies the maximum number of characters to
     produce.  The trailing null character is counted towards this
     limit, so you should allocate at least SIZE characters for the
     string S.  If SIZE is zero, nothing, not even the null byte, shall
     be written and S may be a null pointer.

     The return value is the number of characters which would be
     generated for the given input, excluding the trailing null.  If
     this value is greater than or equal to SIZE, not all characters
     from the result have been stored in S.  You should try again with a
     bigger output string.  Here is an example of doing this:

          /* Construct a message describing the value of a variable
             whose name is NAME and whose value is VALUE. */
          char *
          make_message (char *name, char *value)
          {
            /* Guess we need no more than 100 chars of space. */
            int size = 100;
            char *buffer = (char *) xmalloc (size);
            int nchars;
            if (buffer == NULL)
              return NULL;

           /* Try to print in the allocated space. */
            nchars = snprintf (buffer, size, "value of %s is %s",
          		     name, value);
            if (nchars >= size)
              {
                /* Reallocate buffer now that we know
          	 how much space is needed. */
                size = nchars + 1;
                buffer = (char *) xrealloc (buffer, size);

                if (buffer != NULL)
          	/* Try again. */
          	snprintf (buffer, size, "value of %s is %s",
          		  name, value);
              }
            /* The last call worked, return the string. */
            return buffer;
          }

     In practice, it is often easier just to use ‘asprintf’, below.

     *Attention:* In versions of the GNU C Library prior to 2.1 the
     return value is the number of characters stored, not including the
     terminating null; unless there was not enough space in S to store
     the result in which case ‘-1’ is returned.  This was changed in
     order to comply with the ISO C99 standard.


File: libc.info,  Node: Dynamic Output,  Next: Variable Arguments Output,  Prev: Formatted Output Functions,  Up: Formatted Output

12.12.8 Dynamically Allocating Formatted Output
-----------------------------------------------

The functions in this section do formatted output and place the results
in dynamically allocated memory.

 -- Function: int asprintf (char **PTR, const char *TEMPLATE, …)
     Preliminary: | MT-Safe locale | AS-Unsafe heap | AC-Unsafe mem |
     *Note POSIX Safety Concepts::.

     This function is similar to ‘sprintf’, except that it dynamically
     allocates a string (as with ‘malloc’; *note Unconstrained
     Allocation::) to hold the output, instead of putting the output in
     a buffer you allocate in advance.  The PTR argument should be the
     address of a ‘char *’ object, and a successful call to ‘asprintf’
     stores a pointer to the newly allocated string at that location.

     The return value is the number of characters allocated for the
     buffer, or less than zero if an error occurred.  Usually this means
     that the buffer could not be allocated.

     Here is how to use ‘asprintf’ to get the same result as the
     ‘snprintf’ example, but more easily:

          /* Construct a message describing the value of a variable
             whose name is NAME and whose value is VALUE. */
          char *
          make_message (char *name, char *value)
          {
            char *result;
            if (asprintf (&result, "value of %s is %s", name, value) < 0)
              return NULL;
            return result;
          }

 -- Function: int obstack_printf (struct obstack *OBSTACK, const char
          *TEMPLATE, …)
     Preliminary: | MT-Safe race:obstack locale | AS-Unsafe corrupt heap
     | AC-Unsafe corrupt mem | *Note POSIX Safety Concepts::.

     This function is similar to ‘asprintf’, except that it uses the
     obstack OBSTACK to allocate the space.  *Note Obstacks::.

     The characters are written onto the end of the current object.  To
     get at them, you must finish the object with ‘obstack_finish’
     (*note Growing Objects::).


File: libc.info,  Node: Variable Arguments Output,  Next: Parsing a Template String,  Prev: Dynamic Output,  Up: Formatted Output

12.12.9 Variable Arguments Output Functions
-------------------------------------------

The functions ‘vprintf’ and friends are provided so that you can define
your own variadic ‘printf’-like functions that make use of the same
internals as the built-in formatted output functions.

   The most natural way to define such functions would be to use a
language construct to say, “Call ‘printf’ and pass this template plus
all of my arguments after the first five.” But there is no way to do
this in C, and it would be hard to provide a way, since at the C
language level there is no way to tell how many arguments your function
received.

   Since that method is impossible, we provide alternative functions,
the ‘vprintf’ series, which lets you pass a ‘va_list’ to describe “all
of my arguments after the first five.”

   When it is sufficient to define a macro rather than a real function,
the GNU C compiler provides a way to do this much more easily with
macros.  For example:

     #define myprintf(a, b, c, d, e, rest...) \
     	    printf (mytemplate , ## rest)

*Note (cpp)Variadic Macros::, for details.  But this is limited to
macros, and does not apply to real functions at all.

   Before calling ‘vprintf’ or the other functions listed in this
section, you _must_ call ‘va_start’ (*note Variadic Functions::) to
initialize a pointer to the variable arguments.  Then you can call
‘va_arg’ to fetch the arguments that you want to handle yourself.  This
advances the pointer past those arguments.

   Once your ‘va_list’ pointer is pointing at the argument of your
choice, you are ready to call ‘vprintf’.  That argument and all
subsequent arguments that were passed to your function are used by
‘vprintf’ along with the template that you specified separately.

   *Portability Note:* The value of the ‘va_list’ pointer is
undetermined after the call to ‘vprintf’, so you must not use ‘va_arg’
after you call ‘vprintf’.  Instead, you should call ‘va_end’ to retire
the pointer from service.  You can call ‘va_start’ again and begin
fetching the arguments from the start of the variable argument list.
(Alternatively, you can use ‘va_copy’ to make a copy of the ‘va_list’
pointer before calling ‘vfprintf’.)  Calling ‘vprintf’ does not destroy
the argument list of your function, merely the particular pointer that
you passed to it.

   Prototypes for these functions are declared in ‘stdio.h’.

 -- Function: int vprintf (const char *TEMPLATE, va_list AP)
     Preliminary: | MT-Safe locale | AS-Unsafe corrupt heap | AC-Unsafe
     mem lock corrupt | *Note POSIX Safety Concepts::.

     This function is similar to ‘printf’ except that, instead of taking
     a variable number of arguments directly, it takes an argument list
     pointer AP.

 -- Function: int vwprintf (const wchar_t *TEMPLATE, va_list AP)
     Preliminary: | MT-Safe locale | AS-Unsafe corrupt heap | AC-Unsafe
     mem lock corrupt | *Note POSIX Safety Concepts::.

     This function is similar to ‘wprintf’ except that, instead of
     taking a variable number of arguments directly, it takes an
     argument list pointer AP.

 -- Function: int vfprintf (FILE *STREAM, const char *TEMPLATE, va_list
          AP)
     Preliminary: | MT-Safe locale | AS-Unsafe corrupt heap | AC-Unsafe
     mem lock corrupt | *Note POSIX Safety Concepts::.

     This is the equivalent of ‘fprintf’ with the variable argument list
     specified directly as for ‘vprintf’.

 -- Function: int vfwprintf (FILE *STREAM, const wchar_t *TEMPLATE,
          va_list AP)
     Preliminary: | MT-Safe locale | AS-Unsafe corrupt heap | AC-Unsafe
     mem lock corrupt | *Note POSIX Safety Concepts::.

     This is the equivalent of ‘fwprintf’ with the variable argument
     list specified directly as for ‘vwprintf’.

 -- Function: int vsprintf (char *S, const char *TEMPLATE, va_list AP)
     Preliminary: | MT-Safe locale | AS-Unsafe heap | AC-Unsafe mem |
     *Note POSIX Safety Concepts::.

     This is the equivalent of ‘sprintf’ with the variable argument list
     specified directly as for ‘vprintf’.

 -- Function: int vswprintf (wchar_t *WS, size_t SIZE, const wchar_t
          *TEMPLATE, va_list AP)
     Preliminary: | MT-Safe locale | AS-Unsafe heap | AC-Unsafe mem |
     *Note POSIX Safety Concepts::.

     This is the equivalent of ‘swprintf’ with the variable argument
     list specified directly as for ‘vwprintf’.

 -- Function: int vsnprintf (char *S, size_t SIZE, const char *TEMPLATE,
          va_list AP)
     Preliminary: | MT-Safe locale | AS-Unsafe heap | AC-Unsafe mem |
     *Note POSIX Safety Concepts::.

     This is the equivalent of ‘snprintf’ with the variable argument
     list specified directly as for ‘vprintf’.

 -- Function: int vasprintf (char **PTR, const char *TEMPLATE, va_list
          AP)
     Preliminary: | MT-Safe locale | AS-Unsafe heap | AC-Unsafe mem |
     *Note POSIX Safety Concepts::.

     The ‘vasprintf’ function is the equivalent of ‘asprintf’ with the
     variable argument list specified directly as for ‘vprintf’.

 -- Function: int obstack_vprintf (struct obstack *OBSTACK, const char
          *TEMPLATE, va_list AP)
     Preliminary: | MT-Safe race:obstack locale | AS-Unsafe corrupt heap
     | AC-Unsafe corrupt mem | *Note POSIX Safety Concepts::.

     The ‘obstack_vprintf’ function is the equivalent of
     ‘obstack_printf’ with the variable argument list specified directly
     as for ‘vprintf’.

   Here’s an example showing how you might use ‘vfprintf’.  This is a
function that prints error messages to the stream ‘stderr’, along with a
prefix indicating the name of the program (*note Error Messages::, for a
description of ‘program_invocation_short_name’).

     #include <stdio.h>
     #include <stdarg.h>

     void
     eprintf (const char *template, ...)
     {
       va_list ap;
       extern char *program_invocation_short_name;

       fprintf (stderr, "%s: ", program_invocation_short_name);
       va_start (ap, template);
       vfprintf (stderr, template, ap);
       va_end (ap);
     }

You could call ‘eprintf’ like this:

     eprintf ("file `%s' does not exist\n", filename);

   In GNU C, there is a special construct you can use to let the
compiler know that a function uses a ‘printf’-style format string.  Then
it can check the number and types of arguments in each call to the
function, and warn you when they do not match the format string.  For
example, take this declaration of ‘eprintf’:

     void eprintf (const char *template, ...)
     	__attribute__ ((format (printf, 1, 2)));

This tells the compiler that ‘eprintf’ uses a format string like
‘printf’ (as opposed to ‘scanf’; *note Formatted Input::); the format
string appears as the first argument; and the arguments to satisfy the
format begin with the second.  *Note Declaring Attributes of Functions:
(gcc.info)Function Attributes, for more information.


File: libc.info,  Node: Parsing a Template String,  Next: Example of Parsing,  Prev: Variable Arguments Output,  Up: Formatted Output

12.12.10 Parsing a Template String
----------------------------------

You can use the function ‘parse_printf_format’ to obtain information
about the number and types of arguments that are expected by a given
template string.  This function permits interpreters that provide
interfaces to ‘printf’ to avoid passing along invalid arguments from the
user’s program, which could cause a crash.

   All the symbols described in this section are declared in the header
file ‘printf.h’.

 -- Function: size_t parse_printf_format (const char *TEMPLATE, size_t
          N, int *ARGTYPES)
     Preliminary: | MT-Safe locale | AS-Safe | AC-Safe | *Note POSIX
     Safety Concepts::.

     This function returns information about the number and types of
     arguments expected by the ‘printf’ template string TEMPLATE.  The
     information is stored in the array ARGTYPES; each element of this
     array describes one argument.  This information is encoded using
     the various ‘PA_’ macros, listed below.

     The argument N specifies the number of elements in the array
     ARGTYPES.  This is the maximum number of elements that
     ‘parse_printf_format’ will try to write.

     ‘parse_printf_format’ returns the total number of arguments
     required by TEMPLATE.  If this number is greater than N, then the
     information returned describes only the first N arguments.  If you
     want information about additional arguments, allocate a bigger
     array and call ‘parse_printf_format’ again.

   The argument types are encoded as a combination of a basic type and
modifier flag bits.

 -- Macro: int PA_FLAG_MASK
     This macro is a bitmask for the type modifier flag bits.  You can
     write the expression ‘(argtypes[i] & PA_FLAG_MASK)’ to extract just
     the flag bits for an argument, or ‘(argtypes[i] & ~PA_FLAG_MASK)’
     to extract just the basic type code.

   Here are symbolic constants that represent the basic types; they
stand for integer values.

‘PA_INT’
     This specifies that the base type is ‘int’.

‘PA_CHAR’
     This specifies that the base type is ‘int’, cast to ‘char’.

‘PA_STRING’
     This specifies that the base type is ‘char *’, a null-terminated
     string.

‘PA_POINTER’
     This specifies that the base type is ‘void *’, an arbitrary
     pointer.

‘PA_FLOAT’
     This specifies that the base type is ‘float’.

‘PA_DOUBLE’
     This specifies that the base type is ‘double’.

‘PA_LAST’
     You can define additional base types for your own programs as
     offsets from ‘PA_LAST’.  For example, if you have data types ‘foo’
     and ‘bar’ with their own specialized ‘printf’ conversions, you
     could define encodings for these types as:

          #define PA_FOO  PA_LAST
          #define PA_BAR  (PA_LAST + 1)

   Here are the flag bits that modify a basic type.  They are combined
with the code for the basic type using inclusive-or.

‘PA_FLAG_PTR’
     If this bit is set, it indicates that the encoded type is a pointer
     to the base type, rather than an immediate value.  For example,
     ‘PA_INT|PA_FLAG_PTR’ represents the type ‘int *’.

‘PA_FLAG_SHORT’
     If this bit is set, it indicates that the base type is modified
     with ‘short’.  (This corresponds to the ‘h’ type modifier.)

‘PA_FLAG_LONG’
     If this bit is set, it indicates that the base type is modified
     with ‘long’.  (This corresponds to the ‘l’ type modifier.)

‘PA_FLAG_LONG_LONG’
     If this bit is set, it indicates that the base type is modified
     with ‘long long’.  (This corresponds to the ‘L’ type modifier.)

‘PA_FLAG_LONG_DOUBLE’
     This is a synonym for ‘PA_FLAG_LONG_LONG’, used by convention with
     a base type of ‘PA_DOUBLE’ to indicate a type of ‘long double’.

   For an example of using these facilities, see *note Example of
Parsing::.


File: libc.info,  Node: Example of Parsing,  Prev: Parsing a Template String,  Up: Formatted Output

12.12.11 Example of Parsing a Template String
---------------------------------------------

Here is an example of decoding argument types for a format string.  We
assume this is part of an interpreter which contains arguments of type
‘NUMBER’, ‘CHAR’, ‘STRING’ and ‘STRUCTURE’ (and perhaps others which are
not valid here).

     /* Test whether the NARGS specified objects
        in the vector ARGS are valid
        for the format string FORMAT:
        if so, return 1.
        If not, return 0 after printing an error message.  */

     int
     validate_args (char *format, int nargs, OBJECT *args)
     {
       int *argtypes;
       int nwanted;

       /* Get the information about the arguments.
          Each conversion specification must be at least two characters
          long, so there cannot be more specifications than half the
          length of the string.  */

       argtypes = (int *) alloca (strlen (format) / 2 * sizeof (int));
       nwanted = parse_printf_format (string, nelts, argtypes);

       /* Check the number of arguments.  */
       if (nwanted > nargs)
         {
           error ("too few arguments (at least %d required)", nwanted);
           return 0;
         }

       /* Check the C type wanted for each argument
          and see if the object given is suitable.  */
       for (i = 0; i < nwanted; i++)
         {
           int wanted;

           if (argtypes[i] & PA_FLAG_PTR)
     	wanted = STRUCTURE;
           else
     	switch (argtypes[i] & ~PA_FLAG_MASK)
	       {
     	  case PA_INT:
     	  case PA_FLOAT:
     	  case PA_DOUBLE:
     	    wanted = NUMBER;
     	    break;
     	  case PA_CHAR:
     	    wanted = CHAR;
     	    break;
     	  case PA_STRING:
     	    wanted = STRING;
     	    break;
     	  case PA_POINTER:
     	    wanted = STRUCTURE;
     	    break;
	       }
           if (TYPE (args[i]) != wanted)
	     {
     	  error ("type mismatch for arg number %d", i);
     	  return 0;
	     }
         }
       return 1;
     }


File: libc.info,  Node: Customizing Printf,  Next: Formatted Input,  Prev: Formatted Output,  Up: I/O on Streams

12.13 Customizing ‘printf’
==========================

The GNU C Library lets you define your own custom conversion specifiers
for ‘printf’ template strings, to teach ‘printf’ clever ways to print
the important data structures of your program.

   The way you do this is by registering the conversion with the
function ‘register_printf_function’; see *note Registering New
Conversions::.  One of the arguments you pass to this function is a
pointer to a handler function that produces the actual output; see *note
Defining the Output Handler::, for information on how to write this
function.

   You can also install a function that just returns information about
the number and type of arguments expected by the conversion specifier.
*Note Parsing a Template String::, for information about this.

   The facilities of this section are declared in the header file
‘printf.h’.

* Menu:

* Registering New Conversions::         Using ‘register_printf_function’
					 to register a new output conversion.
* Conversion Specifier Options::        The handler must be able to get
					 the options specified in the
					 template when it is called.
* Defining the Output Handler::         Defining the handler and arginfo
					 functions that are passed as arguments
					 to ‘register_printf_function’.
* Printf Extension Example::            How to define a ‘printf’
					 handler function.
* Predefined Printf Handlers::          Predefined ‘printf’ handlers.

   *Portability Note:* The ability to extend the syntax of ‘printf’
template strings is a GNU extension.  ISO standard C has nothing
similar.


File: libc.info,  Node: Registering New Conversions,  Next: Conversion Specifier Options,  Up: Customizing Printf

12.13.1 Registering New Conversions
-----------------------------------

The function to register a new output conversion is
‘register_printf_function’, declared in ‘printf.h’.

 -- Function: int register_printf_function (int SPEC, printf_function
          HANDLER-FUNCTION, printf_arginfo_function ARGINFO-FUNCTION)
     Preliminary: | MT-Unsafe const:printfext | AS-Unsafe heap lock |
     AC-Unsafe mem lock | *Note POSIX Safety Concepts::.

     This function defines the conversion specifier character SPEC.
     Thus, if SPEC is ‘'Y'’, it defines the conversion ‘%Y’.  You can
     redefine the built-in conversions like ‘%s’, but flag characters
     like ‘#’ and type modifiers like ‘l’ can never be used as
     conversions; calling ‘register_printf_function’ for those
     characters has no effect.  It is advisable not to use lowercase
     letters, since the ISO C standard warns that additional lowercase
     letters may be standardized in future editions of the standard.

     The HANDLER-FUNCTION is the function called by ‘printf’ and friends
     when this conversion appears in a template string.  *Note Defining
     the Output Handler::, for information about how to define a
     function to pass as this argument.  If you specify a null pointer,
     any existing handler function for SPEC is removed.

     The ARGINFO-FUNCTION is the function called by
     ‘parse_printf_format’ when this conversion appears in a template
     string.  *Note Parsing a Template String::, for information about
     this.

     *Attention:* In the GNU C Library versions before 2.0 the
     ARGINFO-FUNCTION function did not need to be installed unless the
     user used the ‘parse_printf_format’ function.  This has changed.
     Now a call to any of the ‘printf’ functions will call this function
     when this format specifier appears in the format string.

     The return value is ‘0’ on success, and ‘-1’ on failure (which
     occurs if SPEC is out of range).

     You can redefine the standard output conversions, but this is
     probably not a good idea because of the potential for confusion.
     Library routines written by other people could break if you do
     this.


File: libc.info,  Node: Conversion Specifier Options,  Next: Defining the Output Handler,  Prev: Registering New Conversions,  Up: Customizing Printf

12.13.2 Conversion Specifier Options
------------------------------------

If you define a meaning for ‘%A’, what if the template contains ‘%+23A’
or ‘%-#A’?  To implement a sensible meaning for these, the handler when
called needs to be able to get the options specified in the template.

   Both the HANDLER-FUNCTION and ARGINFO-FUNCTION accept an argument
that points to a ‘struct printf_info’, which contains information about
the options appearing in an instance of the conversion specifier.  This
data type is declared in the header file ‘printf.h’.

 -- Type: struct printf_info
     This structure is used to pass information about the options
     appearing in an instance of a conversion specifier in a ‘printf’
     template string to the handler and arginfo functions for that
     specifier.  It contains the following members:

     ‘int prec’
          This is the precision specified.  The value is ‘-1’ if no
          precision was specified.  If the precision was given as ‘*’,
          the ‘printf_info’ structure passed to the handler function
          contains the actual value retrieved from the argument list.
          But the structure passed to the arginfo function contains a
          value of ‘INT_MIN’, since the actual value is not known.

     ‘int width’
          This is the minimum field width specified.  The value is ‘0’
          if no width was specified.  If the field width was given as
          ‘*’, the ‘printf_info’ structure passed to the handler
          function contains the actual value retrieved from the argument
          list.  But the structure passed to the arginfo function
          contains a value of ‘INT_MIN’, since the actual value is not
          known.

     ‘wchar_t spec’
          This is the conversion specifier character specified.  It’s
          stored in the structure so that you can register the same
          handler function for multiple characters, but still have a way
          to tell them apart when the handler function is called.

     ‘unsigned int is_long_double’
          This is a boolean that is true if the ‘L’, ‘ll’, or ‘q’ type
          modifier was specified.  For integer conversions, this
          indicates ‘long long int’, as opposed to ‘long double’ for
          floating point conversions.

     ‘unsigned int is_char’
          This is a boolean that is true if the ‘hh’ type modifier was
          specified.

     ‘unsigned int is_short’
          This is a boolean that is true if the ‘h’ type modifier was
          specified.

     ‘unsigned int is_long’
          This is a boolean that is true if the ‘l’ type modifier was
          specified.

     ‘unsigned int alt’
          This is a boolean that is true if the ‘#’ flag was specified.

     ‘unsigned int space’
          This is a boolean that is true if the ‘ ’ flag was specified.

     ‘unsigned int left’
          This is a boolean that is true if the ‘-’ flag was specified.

     ‘unsigned int showsign’
          This is a boolean that is true if the ‘+’ flag was specified.

     ‘unsigned int group’
          This is a boolean that is true if the ‘'’ flag was specified.

     ‘unsigned int extra’
          This flag has a special meaning depending on the context.  It
          could be used freely by the user-defined handlers but when
          called from the ‘printf’ function this variable always
          contains the value ‘0’.

     ‘unsigned int wide’
          This flag is set if the stream is wide oriented.

     ‘wchar_t pad’
          This is the character to use for padding the output to the
          minimum field width.  The value is ‘'0'’ if the ‘0’ flag was
          specified, and ‘' '’ otherwise.