contrib/sendmail/libsm/cdefs.html

   1 <html>
   2 <head>
   3     <title>libsm : C Language Portability Macros</title>
   4 </head>
   5 <body>
   6
   7 <a href="index.html">Back to libsm overview</a>
   8
   9 <center>
  10     <h1> libsm : C Language Portability Macros </h1>
  11     <br> $Id: cdefs.html,v 1.2 2000/12/07 17:33:09 dmoen Exp $
  12 </center>
  13
  14 <h2> Description </h2>
  15
  16 The header file <tt>&lt;sm/cdefs.h&gt;</tt>
  17 defines portable interfaces to non-portable features
  18 of various C compilers.
  19 It also assists you in writing C header files that are compatible
  20 with C++.
  21
  22 <dl>
  23 <dt>
  24 <tt> __P(parameterlist) </tt>
  25 <dd>
  26     This macro is used to write portable function prototypes.
  27     For example,
  28
  29 <blockquote><pre>
  30 int foo __P((int));
  31 </pre></blockquote>
  32
  33 <dt>
  34 <tt> __CONCAT(x,y) </tt>
  35 <dd>
  36     This macro concatenates two tokens x and y,
  37     forming a single token xy.
  38     Warning: make sure there is no white space around the arguments x and y.
  39     <p>
  40
  41 <dt>
  42 <tt> __STRING(x) </tt>
  43 <dd>
  44     This macro converts the token sequence x into a string literal.
  45     <p>
  46
  47 <dt>
  48 <tt> __BEGIN_DECLS, __END_DECLS </tt>
  49 <dd>
  50     These macros are used to write C header files that are compatible
  51     with C++ compilers.
  52     Put <tt>__BEGIN_DECLS</tt> before the first function or variable
  53     declaration in your header file,
  54     and put <tt>__END_DECLS</tt> after the last function or variable
  55     declaration.
  56     <p>
  57
  58 <dt>
  59 <tt> const, signed, volatile </tt>
  60 <dd>
  61     For pre-ANSI C compilers, <tt>const</tt>, <tt>signed</tt>
  62     and <tt>volatile</tt> are defined as empty macros.
  63     This means you can use these keywords without introducing
  64     portability problems.
  65     <p>
  66
  67 <dt>
  68 <tt> SM_DEAD(function_declaration) </tt>
  69 <dd>
  70     This macro modifies a prototype of a function
  71     that does not return to its caller.
  72     With some versions of gcc, this will result in slightly better code,
  73     and can suppress some useless warnings produced by gcc -Wall.
  74     For example,
  75
  76 <blockquote><pre>
  77 SM_DEAD(void exit __P((int)));
  78 </pre></blockquote>
  79
  80 <dt>
  81 <tt> SM_UNUSED(variable_declaration) </tt>
  82 <dd>
  83     This macro modifies a definition of an unused
  84     local variable, global variable or function parameter
  85     in order to suppress compiler warnings.
  86     Examples:
  87
  88 <blockquote><pre>
  89 SM_UNUSED(static const char Id[]) = "@(#)$Id: cdefs.html,v 1.2 2000/12/07 17:33:09 dmoen Exp $";
  90 void
  91 foo(x)
  92         SM_UNUSED(int x);
  93 {
  94         SM_UNUSED(int y) = 0;
  95         return 0;
  96 }
  97 void
  98 bar(SM_UNUSED(int x))
  99 {
 100         return 0;
 101 }
 102 </pre></blockquote>
 103
 104 </dl>
 105
 106 </body>
 107 </html>