1<html lang="en"> 2<head> 3<title>Traditional warnings - The C Preprocessor</title> 4<meta http-equiv="Content-Type" content="text/html"> 5<meta name="description" content="The C Preprocessor"> 6<meta name="generator" content="makeinfo 4.13"> 7<link title="Top" rel="start" href="index.html#Top"> 8<link rel="up" href="Traditional-Mode.html#Traditional-Mode" title="Traditional Mode"> 9<link rel="prev" href="Traditional-miscellany.html#Traditional-miscellany" title="Traditional miscellany"> 10<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage"> 11<!-- 12Copyright (C) 1987, 1989, 1991, 1992, 1993, 1994, 1995, 1996, 131997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 142008, 2009, 2010, 2011 15Free Software Foundation, Inc. 16 17Permission is granted to copy, distribute and/or modify this document 18under the terms of the GNU Free Documentation License, Version 1.3 or 19any later version published by the Free Software Foundation. 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Therefore 77<samp><span class="option">-Wtraditional</span></samp> warns about directives that traditional C 78understands but would ignore because the ‘<samp><span class="samp">#</span></samp>’ does not appear as the 79first character on the line. It also suggests you hide directives like 80‘<samp><span class="samp">#pragma</span></samp>’ not understood by traditional C by indenting them. Some 81traditional implementations would not recognize ‘<samp><span class="samp">#elif</span></samp>’, so it 82suggests avoiding it altogether. 83 84 <li>A function-like macro that appears without an argument list. In some 85traditional preprocessors this was an error. In ISO C it merely means 86that the macro is not expanded. 87 88 <li>The unary plus operator. This did not exist in traditional C. 89 90 <li>The ‘<samp><span class="samp">U</span></samp>’ and ‘<samp><span class="samp">LL</span></samp>’ integer constant suffixes, which were not 91available in traditional C. (Traditional C does support the ‘<samp><span class="samp">L</span></samp>’ 92suffix for simple long integer constants.) You are not warned about 93uses of these suffixes in macros defined in system headers. For 94instance, <code>UINT_MAX</code> may well be defined as <code>4294967295U</code>, but 95you will not be warned if you use <code>UINT_MAX</code>. 96 97 <p>You can usually avoid the warning, and the related warning about 98constants which are so large that they are unsigned, by writing the 99integer constant in question in hexadecimal, with no U suffix. Take 100care, though, because this gives the wrong result in exotic cases. 101</ul> 102 103 </body></html> 104 105