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<html>
<head>
    <title>libsm : C Language Portability Macros</title>
</head>
<body>

<a href="index.html">Back to libsm overview</a>

<center>
    <h1> libsm : C Language Portability Macros </h1>
    <br> $Id: cdefs.html,v 1.2 2000-12-07 17:33:09 dmoen Exp $
</center>

<h2> Description </h2>

The header file <tt>&lt;sm/cdefs.h&gt;</tt>
defines portable interfaces to non-portable features
of various C compilers.
It also assists you in writing C header files that are compatible
with C++.

<dl>
<dt>
<tt> __P(parameterlist) </tt>
<dd>
    This macro is used to write portable function prototypes.
    For example,

<blockquote><pre>
int foo __P((int));
</pre></blockquote>

<dt>
<tt> __CONCAT(x,y) </tt>
<dd>
    This macro concatenates two tokens x and y,
    forming a single token xy.
    Warning: make sure there is no white space around the arguments x and y.
    <p>

<dt>
<tt> __STRING(x) </tt>
<dd>
    This macro converts the token sequence x into a string literal.
    <p>

<dt>
<tt> __BEGIN_DECLS, __END_DECLS </tt>
<dd>
    These macros are used to write C header files that are compatible
    with C++ compilers.
    Put <tt>__BEGIN_DECLS</tt> before the first function or variable
    declaration in your header file,
    and put <tt>__END_DECLS</tt> after the last function or variable
    declaration.
    <p>

<dt>
<tt> const, signed, volatile </tt>
<dd>
    For pre-ANSI C compilers, <tt>const</tt>, <tt>signed</tt>
    and <tt>volatile</tt> are defined as empty macros.
    This means you can use these keywords without introducing
    portability problems.
    <p>

<dt>
<tt> SM_DEAD(function_declaration) </tt>
<dd>
    This macro modifies a prototype of a function
    that does not return to its caller.
    With some versions of gcc, this will result in slightly better code,
    and can suppress some useless warnings produced by gcc -Wall.
    For example,

<blockquote><pre>
SM_DEAD(void exit __P((int)));
</pre></blockquote>

<dt>
<tt> SM_UNUSED(variable_declaration) </tt>
<dd>
    This macro modifies a definition of an unused
    local variable, global variable or function parameter
    in order to suppress compiler warnings.
    Examples:

<blockquote><pre>
SM_UNUSED(static const char Id[]) = "@(#)$Id: cdefs.html,v 1.2 2000-12-07 17:33:09 dmoen Exp $";
void
foo(x)
	SM_UNUSED(int x);
{
	SM_UNUSED(int y) = 0;
	return 0;
}
void
bar(SM_UNUSED(int x))
{
	return 0;
}
</pre></blockquote>

</dl>

</body>
</html>