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<title>The GNU Fortran Compiler: Interoperability with C</title>

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Next: <a href="GNU-Fortran-Compiler-Directives.html#GNU-Fortran-Compiler-Directives" accesskey="n" rel="next">GNU Fortran Compiler Directives</a>, Up: <a href="Mixed_002dLanguage-Programming.html#Mixed_002dLanguage-Programming" accesskey="u" rel="up">Mixed-Language Programming</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>
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<a name="Interoperability-with-C-1"></a>
<h3 class="section">7.1 Interoperability with C</h3>

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<tr><td align="left" valign="top">&bull; <a href="Derived-Types-and-struct.html#Derived-Types-and-struct" accesskey="2">Derived Types and struct</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Interoperable-Global-Variables.html#Interoperable-Global-Variables" accesskey="3">Interoperable Global Variables</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Interoperable-Subroutines-and-Functions.html#Interoperable-Subroutines-and-Functions" accesskey="4">Interoperable Subroutines and Functions</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
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<tr><td align="left" valign="top">&bull; <a href="Working-with-Pointers.html#Working-with-Pointers" accesskey="5">Working with Pointers</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
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<tr><td align="left" valign="top">&bull; <a href="Further-Interoperability-of-Fortran-with-C.html#Further-Interoperability-of-Fortran-with-C" accesskey="6">Further Interoperability of Fortran with C</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
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<p>Since Fortran 2003 (ISO/IEC 1539-1:2004(E)) there is a
standardized way to generate procedure and derived-type
declarations and global variables which are interoperable with C
(ISO/IEC 9899:1999).  The <code>bind(C)</code> attribute has been added
to inform the compiler that a symbol shall be interoperable with C;
also, some constraints are added.  Note, however, that not
all C features have a Fortran equivalent or vice versa.  For instance,
neither C&rsquo;s unsigned integers nor C&rsquo;s functions with variable number
of arguments have an equivalent in Fortran.
</p>
<p>Note that array dimensions are reversely ordered in C and that arrays in
C always start with index 0 while in Fortran they start by default with
1.  Thus, an array declaration <code>A(n,m)</code> in Fortran matches
<code>A[m][n]</code> in C and accessing the element <code>A(i,j)</code> matches
<code>A[j-1][i-1]</code>.  The element following <code>A(i,j)</code> (C: <code>A[j-1][i-1]</code>;
assuming <em>i &lt; n</em>) in memory is <code>A(i+1,j)</code> (C: <code>A[j-1][i]</code>).
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