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<title>The GNU Fortran Compiler: Interoperable Global Variables</title>

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<a name="Interoperable-Global-Variables"></a>
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Next: <a href="Interoperable-Subroutines-and-Functions.html#Interoperable-Subroutines-and-Functions" accesskey="n" rel="next">Interoperable Subroutines and Functions</a>, Previous: <a href="Derived-Types-and-struct.html#Derived-Types-and-struct" accesskey="p" rel="prev">Derived Types and struct</a>, Up: <a href="Interoperability-with-C.html#Interoperability-with-C" accesskey="u" rel="up">Interoperability with C</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="Interoperable-Global-Variables-1"></a>
<h4 class="subsection">7.1.3 Interoperable Global Variables</h4>

<p>Variables can be made accessible from C using the C binding attribute,
optionally together with specifying a binding name.  Those variables
have to be declared in the declaration part of a <code>MODULE</code>,
be of interoperable type, and have neither the <code>pointer</code> nor
the <code>allocatable</code> attribute.
</p>
<div class="smallexample">
<pre class="smallexample">  MODULE m
    USE myType_module
    USE ISO_C_BINDING
    integer(C_INT), bind(C, name=&quot;_MyProject_flags&quot;) :: global_flag
    type(myType), bind(C) :: tp
  END MODULE
</pre></div>

<p>Here, <code>_MyProject_flags</code> is the case-sensitive name of the variable
as seen from C programs while <code>global_flag</code> is the case-insensitive
name as seen from Fortran.  If no binding name is specified, as for
<var>tp</var>, the C binding name is the (lowercase) Fortran binding name.
If a binding name is specified, only a single variable may be after the
double colon.  Note of warning: You cannot use a global variable to
access <var>errno</var> of the C library as the C standard allows it to be
a macro.  Use the <code>IERRNO</code> intrinsic (GNU extension) instead.
</p>


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