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128 lines
5.3 KiB
HTML
128 lines
5.3 KiB
HTML
4 years ago
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<html>
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<!-- Copyright (C) 1987-2018 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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<!-- Created by GNU Texinfo 6.4, http://www.gnu.org/software/texinfo/ -->
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<head>
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<title>Diagnostics (The C Preprocessor)</title>
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<meta name="description" content="Diagnostics (The C Preprocessor)">
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<meta name="keywords" content="Diagnostics (The C Preprocessor)">
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<meta name="resource-type" content="document">
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<meta name="distribution" content="global">
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<meta name="Generator" content="makeinfo">
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<link href="index.html#Top" rel="start" title="Top">
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<link href="Index-of-Directives.html#Index-of-Directives" rel="index" title="Index of Directives">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="index.html#Top" rel="up" title="Top">
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<link href="Line-Control.html#Line-Control" rel="next" title="Line Control">
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<link href="Deleted-Code.html#Deleted-Code" rel="prev" title="Deleted Code">
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<style type="text/css">
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<!--
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a.summary-letter {text-decoration: none}
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blockquote.indentedblock {margin-right: 0em}
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blockquote.smallindentedblock {margin-right: 0em; font-size: smaller}
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blockquote.smallquotation {font-size: smaller}
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div.display {margin-left: 3.2em}
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div.example {margin-left: 3.2em}
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div.lisp {margin-left: 3.2em}
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div.smalldisplay {margin-left: 3.2em}
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div.smallexample {margin-left: 3.2em}
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div.smalllisp {margin-left: 3.2em}
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kbd {font-style: oblique}
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pre.display {font-family: inherit}
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pre.format {font-family: inherit}
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pre.menu-comment {font-family: serif}
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pre.menu-preformatted {font-family: serif}
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pre.smalldisplay {font-family: inherit; font-size: smaller}
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pre.smallexample {font-size: smaller}
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pre.smallformat {font-family: inherit; font-size: smaller}
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pre.smalllisp {font-size: smaller}
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span.nolinebreak {white-space: nowrap}
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span.roman {font-family: initial; font-weight: normal}
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span.sansserif {font-family: sans-serif; font-weight: normal}
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ul.no-bullet {list-style: none}
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-->
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</style>
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</head>
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<body lang="en">
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<a name="Diagnostics"></a>
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<div class="header">
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<p>
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Next: <a href="Line-Control.html#Line-Control" accesskey="n" rel="next">Line Control</a>, Previous: <a href="Conditionals.html#Conditionals" accesskey="p" rel="prev">Conditionals</a>, Up: <a href="index.html#Top" accesskey="u" rel="up">Top</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Index-of-Directives.html#Index-of-Directives" title="Index" rel="index">Index</a>]</p>
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</div>
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<hr>
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<a name="Diagnostics-1"></a>
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<h2 class="chapter">5 Diagnostics</h2>
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<a name="index-diagnostic"></a>
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<a name="index-reporting-errors"></a>
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<a name="index-reporting-warnings"></a>
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<a name="index-_0023error"></a>
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<p>The directive ‘<samp>#error</samp>’ causes the preprocessor to report a fatal
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error. The tokens forming the rest of the line following ‘<samp>#error</samp>’
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are used as the error message.
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</p>
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<p>You would use ‘<samp>#error</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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</p>
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<div class="smallexample">
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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></div>
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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>#error</samp>’. For example,
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</p>
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<div class="smallexample">
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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></div>
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<a name="index-_0023warning"></a>
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<p>The directive ‘<samp>#warning</samp>’ is like ‘<samp>#error</samp>’, but causes the
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preprocessor to issue a warning and continue preprocessing. The tokens
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following ‘<samp>#warning</samp>’ are used as the warning message.
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</p>
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<p>You might use ‘<samp>#warning</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>
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<p>Neither ‘<samp>#error</samp>’ nor ‘<samp>#warning</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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</p>
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</body>
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</html>
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