1<html lang="en"> 2<head> 3<title>Diagnostics - 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="prev" href="Conditionals.html#Conditionals" title="Conditionals"> 9<link rel="next" href="Line-Control.html#Line-Control" title="Line Control"> 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. A copy of 20the license is included in the 21section entitled ``GNU Free Documentation License''. 22 23This manual contains no Invariant Sections. The Front-Cover Texts are 24(a) (see below), and the Back-Cover Texts are (b) (see below). 25 26(a) The FSF's Front-Cover Text is: 27 28 A GNU Manual 29 30(b) The FSF's Back-Cover Text is: 31 32 You have freedom to copy and modify this GNU Manual, like GNU 33 software. Copies published by the Free Software Foundation raise 34 funds for GNU development. 35--> 36<meta http-equiv="Content-Style-Type" content="text/css"> 37<style type="text/css"><!-- 38 pre.display { font-family:inherit } 39 pre.format { font-family:inherit } 40 pre.smalldisplay { font-family:inherit; font-size:smaller } 41 pre.smallformat { font-family:inherit; font-size:smaller } 42 pre.smallexample { font-size:smaller } 43 pre.smalllisp { font-size:smaller } 44 span.sc { font-variant:small-caps } 45 span.roman { font-family:serif; font-weight:normal; } 46 span.sansserif { font-family:sans-serif; font-weight:normal; } 47--></style> 48<link rel="stylesheet" type="text/css" href="../cs.css"> 49</head> 50<body> 51<div class="node"> 52<a name="Diagnostics"></a> 53<p> 54Next: <a rel="next" accesskey="n" href="Line-Control.html#Line-Control">Line Control</a>, 55Previous: <a rel="previous" accesskey="p" href="Conditionals.html#Conditionals">Conditionals</a>, 56Up: <a rel="up" accesskey="u" href="index.html#Top">Top</a> 57<hr> 58</div> 59 60<h2 class="chapter">5 Diagnostics</h2> 61 62<p><a name="index-diagnostic-93"></a><a name="index-reporting-errors-94"></a><a name="index-reporting-warnings-95"></a> 63<a name="index-g_t_0023error-96"></a>The directive ‘<samp><span class="samp">#error</span></samp>’ causes the preprocessor to report a fatal 64error. The tokens forming the rest of the line following ‘<samp><span class="samp">#error</span></samp>’ 65are used as the error message. 66 67 <p>You would use ‘<samp><span class="samp">#error</span></samp>’ inside of a conditional that detects a 68combination of parameters which you know the program does not properly 69support. For example, if you know that the program will not run 70properly on a VAX, you might write 71 72<pre class="smallexample"> #ifdef __vax__ 73 #error "Won't work on VAXen. See comments at get_last_object." 74 #endif 75</pre> 76 <p>If you have several configuration parameters that must be set up by 77the installation in a consistent way, you can use conditionals to detect 78an inconsistency and report it with ‘<samp><span class="samp">#error</span></samp>’. For example, 79 80<pre class="smallexample"> #if !defined(UNALIGNED_INT_ASM_OP) && defined(DWARF2_DEBUGGING_INFO) 81 #error "DWARF2_DEBUGGING_INFO requires UNALIGNED_INT_ASM_OP." 82 #endif 83</pre> 84 <p><a name="index-g_t_0023warning-97"></a>The directive ‘<samp><span class="samp">#warning</span></samp>’ is like ‘<samp><span class="samp">#error</span></samp>’, but causes the 85preprocessor to issue a warning and continue preprocessing. The tokens 86following ‘<samp><span class="samp">#warning</span></samp>’ are used as the warning message. 87 88 <p>You might use ‘<samp><span class="samp">#warning</span></samp>’ in obsolete header files, with a message 89directing the user to the header file which should be used instead. 90 91 <p>Neither ‘<samp><span class="samp">#error</span></samp>’ nor ‘<samp><span class="samp">#warning</span></samp>’ macro-expands its argument. 92Internal whitespace sequences are each replaced with a single space. 93The line must consist of complete tokens. It is wisest to make the 94argument of these directives be a single string constant; this avoids 95problems with apostrophes and the like. 96 97 </body></html> 98 99