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Function-Attributes.html

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  24. <title>Using the GNU Compiler Collection (GCC): Function Attributes</title>
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  36. <link href="Common-Function-Attributes.html#Common-Function-Attributes" rel="next" title="Common Function Attributes">
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    71. 

  71. <a name="Function-Attributes"></a>
    72. 

  72. <div class="header">
    73. 

  73. <p>
    74. 

  74. Next: <a href="Variable-Attributes.html#Variable-Attributes" accesskey="n" rel="next">Variable Attributes</a>, Previous: <a href="Mixed-Declarations.html#Mixed-Declarations" accesskey="p" rel="prev">Mixed Declarations</a>, Up: <a href="C-Extensions.html#C-Extensions" accesskey="u" rel="up">C Extensions</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
    75. 

  75. </div>
    76. 

  76. <hr>
    77. 

  77. <a name="Declaring-Attributes-of-Functions"></a>
    78. 

  78. <h3 class="section">6.31 Declaring Attributes of Functions</h3>
    79. 

  79. <a name="index-function-attributes"></a>
    80. 

  80. <a name="index-declaring-attributes-of-functions"></a>
    81. 

  81. <a name="index-volatile-applied-to-function"></a>
    82. 

  82. <a name="index-const-applied-to-function"></a>
    83. 

  83. 

  84. <p>In GNU C, you can use function attributes to declare certain things
    85. 

  85. about functions called in your program which help the compiler
    86. 

  86. optimize calls and check your code more carefully.  For example, you
    87. 

  87. can use attributes to declare that a function never returns
    88. 

  88. (<code>noreturn</code>), returns a value depending only on its arguments
    89. 

  89. (<code>pure</code>), or has <code>printf</code>-style arguments (<code>format</code>).
    90. 

  90. </p>
    91. 

  91. <p>You can also use attributes to control memory placement, code
    92. 

  92. generation options or call/return conventions within the function
    93. 

  93. being annotated.  Many of these attributes are target-specific.  For
    94. 

  94. example, many targets support attributes for defining interrupt
    95. 

  95. handler functions, which typically must follow special register usage
    96. 

  96. and return conventions.
    97. 

  97. </p>
    98. 

  98. <p>Function attributes are introduced by the <code>__attribute__</code> keyword
    99. 

  99. on a declaration, followed by an attribute specification inside double
    100. 

  100. parentheses.  You can specify multiple attributes in a declaration by
    101. 

  101. separating them by commas within the double parentheses or by
    102. 

  102. immediately following an attribute declaration with another attribute
    103. 

  103. declaration.  See <a href="Attribute-Syntax.html#Attribute-Syntax">Attribute Syntax</a>, for the exact rules on
    104. 

  104. attribute syntax and placement.
    105. 

  105. </p>
    106. 

  106. <p>GCC also supports attributes on
    107. 

  107. variable declarations (see <a href="Variable-Attributes.html#Variable-Attributes">Variable Attributes</a>),
    108. 

  108. labels (see <a href="Label-Attributes.html#Label-Attributes">Label Attributes</a>),
    109. 

  109. enumerators (see <a href="Enumerator-Attributes.html#Enumerator-Attributes">Enumerator Attributes</a>),
    110. 

  110. statements (see <a href="Statement-Attributes.html#Statement-Attributes">Statement Attributes</a>),
    111. 

  111. and types (see <a href="Type-Attributes.html#Type-Attributes">Type Attributes</a>).
    112. 

  112. </p>
    113. 

  113. <p>There is some overlap between the purposes of attributes and pragmas
    114. 

  114. (see <a href="Pragmas.html#Pragmas">Pragmas Accepted by GCC</a>).  It has been
    115. 

  115. found convenient to use <code>__attribute__</code> to achieve a natural
    116. 

  116. attachment of attributes to their corresponding declarations, whereas
    117. 

  117. <code>#pragma</code> is of use for compatibility with other compilers
    118. 

  118. or constructs that do not naturally form part of the grammar.
    119. 

  119. </p>
    120. 

  120. <p>In addition to the attributes documented here,
    121. 

  121. GCC plugins may provide their own attributes.
    122. 

  122. </p>
    123. 

  123. <table class="menu" border="0" cellspacing="0">
    124. 

  124. <tr><td align="left" valign="top">&bull; <a href="Common-Function-Attributes.html#Common-Function-Attributes" accesskey="1">Common Function Attributes</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
    125. 

  125. </td></tr>
    126. 

  126. <tr><td align="left" valign="top">&bull; <a href="AArch64-Function-Attributes.html#AArch64-Function-Attributes" accesskey="2">AArch64 Function Attributes</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
    127. 

  127. </td></tr>
    128. 

  128. <tr><td align="left" valign="top">&bull; <a href="ARC-Function-Attributes.html#ARC-Function-Attributes" accesskey="3">ARC Function Attributes</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
    129. 

  129. </td></tr>
    130. 

  130. <tr><td align="left" valign="top">&bull; <a href="ARM-Function-Attributes.html#ARM-Function-Attributes" accesskey="4">ARM Function Attributes</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
    131. 

  131. </td></tr>
    132. 

  132. <tr><td align="left" valign="top">&bull; <a href="AVR-Function-Attributes.html#AVR-Function-Attributes" accesskey="5">AVR Function Attributes</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
    133. 

  133. </td></tr>
    134. 

  134. <tr><td align="left" valign="top">&bull; <a href="Blackfin-Function-Attributes.html#Blackfin-Function-Attributes" accesskey="6">Blackfin Function Attributes</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
    135. 

  135. </td></tr>
    136. 

  136. <tr><td align="left" valign="top">&bull; <a href="CR16-Function-Attributes.html#CR16-Function-Attributes" accesskey="7">CR16 Function Attributes</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
    137. 

  137. </td></tr>
    138. 

  138. <tr><td align="left" valign="top">&bull; <a href="Epiphany-Function-Attributes.html#Epiphany-Function-Attributes" accesskey="8">Epiphany Function Attributes</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
    139. 

  139. </td></tr>
    140. 

  140. <tr><td align="left" valign="top">&bull; <a href="H8_002f300-Function-Attributes.html#H8_002f300-Function-Attributes" accesskey="9">H8/300 Function Attributes</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
    141. 

  141. </td></tr>
    142. 

  142. <tr><td align="left" valign="top">&bull; <a href="IA_002d64-Function-Attributes.html#IA_002d64-Function-Attributes">IA-64 Function Attributes</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
    143. 

  143. </td></tr>
    144. 

  144. <tr><td align="left" valign="top">&bull; <a href="M32C-Function-Attributes.html#M32C-Function-Attributes">M32C Function Attributes</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
    145. 

  145. </td></tr>
    146. 

  146. <tr><td align="left" valign="top">&bull; <a href="M32R_002fD-Function-Attributes.html#M32R_002fD-Function-Attributes">M32R/D Function Attributes</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
    147. 

  147. </td></tr>
    148. 

  148. <tr><td align="left" valign="top">&bull; <a href="m68k-Function-Attributes.html#m68k-Function-Attributes">m68k Function Attributes</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
    149. 

  149. </td></tr>
    150. 

  150. <tr><td align="left" valign="top">&bull; <a href="MCORE-Function-Attributes.html#MCORE-Function-Attributes">MCORE Function Attributes</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
    151. 

  151. </td></tr>
    152. 

  152. <tr><td align="left" valign="top">&bull; <a href="MeP-Function-Attributes.html#MeP-Function-Attributes">MeP Function Attributes</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
    153. 

  153. </td></tr>
    154. 

  154. <tr><td align="left" valign="top">&bull; <a href="MicroBlaze-Function-Attributes.html#MicroBlaze-Function-Attributes">MicroBlaze Function Attributes</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
    155. 

  155. </td></tr>
    156. 

  156. <tr><td align="left" valign="top">&bull; <a href="Microsoft-Windows-Function-Attributes.html#Microsoft-Windows-Function-Attributes">Microsoft Windows Function Attributes</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
    157. 

  157. </td></tr>
    158. 

  158. <tr><td align="left" valign="top">&bull; <a href="MIPS-Function-Attributes.html#MIPS-Function-Attributes">MIPS Function Attributes</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
    159. 

  159. </td></tr>
    160. 

  160. <tr><td align="left" valign="top">&bull; <a href="MSP430-Function-Attributes.html#MSP430-Function-Attributes">MSP430 Function Attributes</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
    161. 

  161. </td></tr>
    162. 

  162. <tr><td align="left" valign="top">&bull; <a href="NDS32-Function-Attributes.html#NDS32-Function-Attributes">NDS32 Function Attributes</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
    163. 

  163. </td></tr>
    164. 

  164. <tr><td align="left" valign="top">&bull; <a href="Nios-II-Function-Attributes.html#Nios-II-Function-Attributes">Nios II Function Attributes</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
    165. 

  165. </td></tr>
    166. 

  166. <tr><td align="left" valign="top">&bull; <a href="Nvidia-PTX-Function-Attributes.html#Nvidia-PTX-Function-Attributes">Nvidia PTX Function Attributes</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
    167. 

  167. </td></tr>
    168. 

  168. <tr><td align="left" valign="top">&bull; <a href="PowerPC-Function-Attributes.html#PowerPC-Function-Attributes">PowerPC Function Attributes</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
    169. 

  169. </td></tr>
    170. 

  170. <tr><td align="left" valign="top">&bull; <a href="RL78-Function-Attributes.html#RL78-Function-Attributes">RL78 Function Attributes</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
    171. 

  171. </td></tr>
    172. 

  172. <tr><td align="left" valign="top">&bull; <a href="RX-Function-Attributes.html#RX-Function-Attributes">RX Function Attributes</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
    173. 

  173. </td></tr>
    174. 

  174. <tr><td align="left" valign="top">&bull; <a href="S_002f390-Function-Attributes.html#S_002f390-Function-Attributes">S/390 Function Attributes</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
    175. 

  175. </td></tr>
    176. 

  176. <tr><td align="left" valign="top">&bull; <a href="SH-Function-Attributes.html#SH-Function-Attributes">SH Function Attributes</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
    177. 

  177. </td></tr>
    178. 

  178. <tr><td align="left" valign="top">&bull; <a href="SPU-Function-Attributes.html#SPU-Function-Attributes">SPU Function Attributes</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
    179. 

  179. </td></tr>
    180. 

  180. <tr><td align="left" valign="top">&bull; <a href="Symbian-OS-Function-Attributes.html#Symbian-OS-Function-Attributes">Symbian OS Function Attributes</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
    181. 

  181. </td></tr>
    182. 

  182. <tr><td align="left" valign="top">&bull; <a href="V850-Function-Attributes.html#V850-Function-Attributes">V850 Function Attributes</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
    183. 

  183. </td></tr>
    184. 

  184. <tr><td align="left" valign="top">&bull; <a href="Visium-Function-Attributes.html#Visium-Function-Attributes">Visium Function Attributes</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
    185. 

  185. </td></tr>
    186. 

  186. <tr><td align="left" valign="top">&bull; <a href="x86-Function-Attributes.html#x86-Function-Attributes">x86 Function Attributes</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
    187. 

  187. </td></tr>
    188. 

  188. <tr><td align="left" valign="top">&bull; <a href="Xstormy16-Function-Attributes.html#Xstormy16-Function-Attributes">Xstormy16 Function Attributes</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
    189. 

  189. </td></tr>
    190. 

  190. </table>
    191. 

  191. 

  192. <hr>
    193. 

  193. <div class="header">
    194. 

  194. <p>
    195. 

  195. Next: <a href="Variable-Attributes.html#Variable-Attributes" accesskey="n" rel="next">Variable Attributes</a>, Previous: <a href="Mixed-Declarations.html#Mixed-Declarations" accesskey="p" rel="prev">Mixed Declarations</a>, Up: <a href="C-Extensions.html#C-Extensions" accesskey="u" rel="up">C Extensions</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
    196. 

  196. </div>
    197. 

  197. 

  198. 

  199. 

  200. </body>
    201. 

  201. </html>
    202.