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95 lines
4.4 KiB
HTML
95 lines
4.4 KiB
HTML
4 years ago
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<html lang="en">
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<head>
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<title>Diagnostics - The C Preprocessor</title>
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<meta http-equiv="Content-Type" content="text/html">
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<meta name="description" content="The C Preprocessor">
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<meta name="generator" content="makeinfo 4.13">
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<link title="Top" rel="start" href="index.html#Top">
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<link rel="prev" href="Conditionals.html#Conditionals" title="Conditionals">
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<link rel="next" href="Line-Control.html#Line-Control" title="Line Control">
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<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage">
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<!--
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Copyright (C) 1987-2015 Free Software Foundation, Inc.
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.3 or
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any later version published by the Free Software Foundation. A copy of
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the license is included in the
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section entitled ``GNU Free Documentation License''.
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This manual contains no Invariant Sections. The Front-Cover Texts are
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(a) (see below), and the Back-Cover Texts are (b) (see below).
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(a) The FSF's Front-Cover Text is:
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A GNU Manual
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(b) The FSF's Back-Cover Text is:
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You have freedom to copy and modify this GNU Manual, like GNU
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software. Copies published by the Free Software Foundation raise
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funds for GNU development.
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-->
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<meta http-equiv="Content-Style-Type" content="text/css">
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<style type="text/css"><!--
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pre.display { font-family:inherit }
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pre.format { font-family:inherit }
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pre.smalldisplay { font-family:inherit; font-size:smaller }
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pre.smallformat { font-family:inherit; font-size:smaller }
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pre.smallexample { font-size:smaller }
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pre.smalllisp { font-size:smaller }
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span.sc { font-variant:small-caps }
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span.roman { font-family:serif; font-weight:normal; }
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span.sansserif { font-family:sans-serif; font-weight:normal; }
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--></style>
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</head>
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<body>
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<div class="node">
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<a name="Diagnostics"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="Line-Control.html#Line-Control">Line Control</a>,
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Previous: <a rel="previous" accesskey="p" href="Conditionals.html#Conditionals">Conditionals</a>,
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Up: <a rel="up" accesskey="u" href="index.html#Top">Top</a>
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<hr>
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</div>
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<h2 class="chapter">5 Diagnostics</h2>
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<p><a name="index-diagnostic-93"></a><a name="index-reporting-errors-94"></a><a name="index-reporting-warnings-95"></a>
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<a name="index-g_t_0023error-96"></a>The directive ‘<samp><span class="samp">#error</span></samp>’ causes the preprocessor to report a fatal
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error. The tokens forming the rest of the line following ‘<samp><span class="samp">#error</span></samp>’
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are used as the error message.
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<p>You would use ‘<samp><span class="samp">#error</span></samp>’ inside of a conditional that detects a
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combination of parameters which you know the program does not properly
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support. For example, if you know that the program will not run
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properly on a VAX, you might write
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<pre class="smallexample"> #ifdef __vax__
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#error "Won't work on VAXen. See comments at get_last_object."
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#endif
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</pre>
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<p>If you have several configuration parameters that must be set up by
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the installation in a consistent way, you can use conditionals to detect
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an inconsistency and report it with ‘<samp><span class="samp">#error</span></samp>’. For example,
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<pre class="smallexample"> #if !defined(FOO) && defined(BAR)
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#error "BAR requires FOO."
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#endif
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</pre>
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<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
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preprocessor to issue a warning and continue preprocessing. The tokens
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following ‘<samp><span class="samp">#warning</span></samp>’ are used as the warning message.
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<p>You might use ‘<samp><span class="samp">#warning</span></samp>’ in obsolete header files, with a message
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directing the user to the header file which should be used instead.
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<p>Neither ‘<samp><span class="samp">#error</span></samp>’ nor ‘<samp><span class="samp">#warning</span></samp>’ macro-expands its argument.
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Internal whitespace sequences are each replaced with a single space.
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The line must consist of complete tokens. It is wisest to make the
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argument of these directives be a single string constant; this avoids
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problems with apostrophes and the like.
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</body></html>
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