2002-02-17 21:56:45 +00:00
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<title>libsm : C Language Portability Macros</title>
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<a href="index.html">Back to libsm overview</a>
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<center>
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<h1> libsm : C Language Portability Macros </h1>
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2002-06-11 21:12:04 +00:00
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<br> $Id: cdefs.html,v 1.2 2000/12/07 17:33:09 dmoen Exp $
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2002-02-17 21:56:45 +00:00
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</center>
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<h2> Description </h2>
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The header file <tt><sm/cdefs.h></tt>
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defines portable interfaces to non-portable features
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of various C compilers.
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It also assists you in writing C header files that are compatible
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with C++.
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<dl>
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<dt>
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<tt> __P(parameterlist) </tt>
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<dd>
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This macro is used to write portable function prototypes.
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For example,
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<blockquote><pre>
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int foo __P((int));
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</pre></blockquote>
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<dt>
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<tt> __CONCAT(x,y) </tt>
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<dd>
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This macro concatenates two tokens x and y,
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forming a single token xy.
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Warning: make sure there is no white space around the arguments x and y.
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<p>
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<dt>
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<tt> __STRING(x) </tt>
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<dd>
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This macro converts the token sequence x into a string literal.
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<p>
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<dt>
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<tt> __BEGIN_DECLS, __END_DECLS </tt>
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<dd>
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These macros are used to write C header files that are compatible
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with C++ compilers.
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Put <tt>__BEGIN_DECLS</tt> before the first function or variable
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declaration in your header file,
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and put <tt>__END_DECLS</tt> after the last function or variable
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declaration.
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<p>
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<dt>
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<tt> const, signed, volatile </tt>
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<dd>
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For pre-ANSI C compilers, <tt>const</tt>, <tt>signed</tt>
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and <tt>volatile</tt> are defined as empty macros.
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This means you can use these keywords without introducing
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portability problems.
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<p>
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<dt>
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<tt> SM_DEAD(function_declaration) </tt>
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<dd>
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This macro modifies a prototype of a function
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that does not return to its caller.
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With some versions of gcc, this will result in slightly better code,
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and can suppress some useless warnings produced by gcc -Wall.
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For example,
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<blockquote><pre>
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SM_DEAD(void exit __P((int)));
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</pre></blockquote>
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<dt>
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<tt> SM_UNUSED(variable_declaration) </tt>
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<dd>
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This macro modifies a definition of an unused
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local variable, global variable or function parameter
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in order to suppress compiler warnings.
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Examples:
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<blockquote><pre>
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2002-06-11 21:12:04 +00:00
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SM_UNUSED(static const char Id[]) = "@(#)$Id: cdefs.html,v 1.2 2000/12/07 17:33:09 dmoen Exp $";
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2002-02-17 21:56:45 +00:00
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void
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foo(x)
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SM_UNUSED(int x);
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{
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SM_UNUSED(int y) = 0;
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return 0;
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}
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void
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bar(SM_UNUSED(int x))
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{
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return 0;
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}
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</pre></blockquote>
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</dl>
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</body>
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</html>
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