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 16The header file <tt><sm/cdefs.h></tt> 17defines portable interfaces to non-portable features 18of various C compilers. 19It also assists you in writing C header files that are compatible 20with 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> 30int 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> 77SM_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> 89SM_UNUSED(static const char Id[]) = "@(#)$Id: cdefs.html,v 1.2 2000-12-07 17:33:09 dmoen Exp $"; 90void 91foo(x) 92 SM_UNUSED(int x); 93{ 94 SM_UNUSED(int y) = 0; 95 return 0; 96} 97void 98bar(SM_UNUSED(int x)) 99{ 100 return 0; 101} 102</pre></blockquote> 103 104</dl> 105 106</body> 107</html> 108