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| <title>The C Preprocessor: Diagnostics</title> |
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| <a name="Diagnostics"></a> |
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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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| <a name="Diagnostics-1"></a> |
| <h2 class="chapter">5 Diagnostics</h2> |
| <a name="index-diagnostic"></a> |
| <a name="index-reporting-errors"></a> |
| <a name="index-reporting-warnings"></a> |
| |
| <a name="index-_0023error"></a> |
| <p>The directive ‘<samp>#error</samp>’ causes the preprocessor to report a fatal |
| error. The tokens forming the rest of the line following ‘<samp>#error</samp>’ |
| are used as the error message. |
| </p> |
| <p>You would use ‘<samp>#error</samp>’ inside of a conditional that detects a |
| combination of parameters which you know the program does not properly |
| support. For example, if you know that the program will not run |
| properly on a VAX, you might write |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">#ifdef __vax__ |
| #error "Won't work on VAXen. See comments at get_last_object." |
| #endif |
| </pre></div> |
| |
| <p>If you have several configuration parameters that must be set up by |
| the installation in a consistent way, you can use conditionals to detect |
| an inconsistency and report it with ‘<samp>#error</samp>’. For example, |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">#if !defined(FOO) && defined(BAR) |
| #error "BAR requires FOO." |
| #endif |
| </pre></div> |
| |
| <a name="index-_0023warning"></a> |
| <p>The directive ‘<samp>#warning</samp>’ is like ‘<samp>#error</samp>’, but causes the |
| preprocessor to issue a warning and continue preprocessing. The tokens |
| following ‘<samp>#warning</samp>’ are used as the warning message. |
| </p> |
| <p>You might use ‘<samp>#warning</samp>’ in obsolete header files, with a message |
| directing the user to the header file which should be used instead. |
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