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| 22 | <title>Signals (GNU C Language Manual)</title>
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| 57 | <body lang="en">
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| 58 | <span id="Signals"></span><div class="header">
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| 59 | <p>
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| 60 | Next: <a href="GNU-Free-Documentation-License.html" accesskey="n" rel="next">GNU Free Documentation License</a>, Previous: <a href="Attributes.html" accesskey="p" rel="prev">Attributes</a>, Up: <a href="index.html" accesskey="u" rel="up">Top</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Symbol-Index.html" title="Index" rel="index">Index</a>]</p>
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| 61 | </div>
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| 62 | <hr>
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| 63 | <span id="Signals-1"></span><h2 class="appendix">Appendix E Signals</h2>
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| 64 | <span id="index-signal"></span>
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| 65 | <span id="index-handler-_0028for-signal_0029"></span>
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| 66 | <span id="index-SIGSEGV"></span>
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| 67 | <span id="index-SIGFPE"></span>
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| 68 | <span id="index-SIGBUS"></span>
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| 69 |
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| 70 | <p>Some program operations bring about an error condition called a
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| 71 | <em>signal</em>. These signals terminate the program, by default.
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| 72 | </p>
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| 73 | <p>There are various different kinds of signals, each with a name. We
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| 74 | have seen several such error conditions through this manual:
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| 75 | </p>
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| 76 | <dl compact="compact">
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| 77 | <dt><code>SIGSEGV</code></dt>
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| 78 | <dd><p>This signal is generated when a program tries to read or write outside
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| 79 | the memory that is allocated for it, or to write memory that can only
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| 80 | be read. The name is an abbreviation for “segmentation violation”.
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| 81 | </p>
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| 82 | </dd>
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| 83 | <dt><code>SIGFPE</code></dt>
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| 84 | <dd><p>This signal indicates a fatal arithmetic error. The name is an
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| 85 | abbreviation for “floating-point exception”, but covers all types of
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| 86 | arithmetic errors, including division by zero and overflow.
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| 87 | </p>
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| 88 | </dd>
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| 89 | <dt><code>SIGBUS</code></dt>
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| 90 | <dd><p>This signal is generated when an invalid pointer is dereferenced,
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| 91 | typically the result of dereferencing an uninintalized pointer. It is
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| 92 | similar to <code>SIGSEGV</code>, except that <code>SIGSEGV</code> indicates
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| 93 | invalid access to valid memory, while <code>SIGBUS</code> indicates an
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| 94 | attempt to access an invalid address.
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| 95 | </p></dd>
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| 96 | </dl>
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| 97 |
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| 98 | <p>These kinds of signal allow the program to specify a function as a
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| 99 | <em>signal handler</em>. When a signal has a handler, it doesn’t
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| 100 | terminate the program; instead it calls the handler.
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| 101 | </p>
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| 102 | <p>There are many other kinds of signal; here we list only those that
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| 103 | come from run-time errors in C operations. The rest have to do with
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| 104 | the functioning of the operating system. The GNU C Library Reference
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| 105 | Manual gives more explanation about signals (see <a href="https://www.gnu.org/software/libc/manual/html_node/Program-Signal-Handling.html#Program-Signal-Handling">The GNU C Library</a> in <cite>The GNU C Library Reference
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| 106 | Manual</cite>).
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| 107 | </p>
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