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<h3 class="section">7.2 GNU Fortran Compiler Directives</h3>
<p>The Fortran standard standard describes how a conforming program shall
behave; however, the exact implementation is not standardized. In order
to allow the user to choose specific implementation details, compiler
directives can be used to set attributes of variables and procedures
which are not part of the standard. Whether a given attribute is
supported and its exact effects depend on both the operating system and
on the processor; see
<a href="../gcc/index.html#Top">C Extensions</a>
for details.
<p>For procedures and procedure pointers, the following attributes can
be used to change the calling convention:
<ul>
<li><code>CDECL</code> – standard C calling convention
<li><code>STDCALL</code> – convention where the called procedure pops the stack
<li><code>FASTCALL</code> – part of the arguments are passed via registers
instead using the stack
</ul>
<p>Besides changing the calling convention, the attributes also influence
the decoration of the symbol name, e.g., by a leading underscore or by
a trailing at-sign followed by the number of bytes on the stack. When
assigning a procedure to a procedure pointer, both should use the same
calling convention.
<p>On some systems, procedures and global variables (module variables and
<code>COMMON</code> blocks) need special handling to be accessible when they
are in a shared library. The following attributes are available:
<ul>
<li><code>DLLEXPORT</code> – provide a global pointer to a pointer in the DLL
<li><code>DLLIMPORT</code> – reference the function or variable using a global pointer
</ul>
<p>The attributes are specified using the syntax
<p><code>!GCC$ ATTRIBUTES</code> <var>attribute-list</var> <code>::</code> <var>variable-list</var>
<p>where in free-form source code only whitespace is allowed before <code>!GCC$</code>
and in fixed-form source code <code>!GCC$</code>, <code>cGCC$</code> or <code>*GCC$</code> shall
start in the first column.
<p>For procedures, the compiler directives shall be placed into the body
of the procedure; for variables and procedure pointers, they shall be in
the same declaration part as the variable or procedure pointer.
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