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<a name="Signals"></a>
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<div class="header">
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<p>
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Next: <a href="Timefns.html#Timefns" accesskey="n" rel="next">Timefns</a>, Previous: <a href="Wchar-strings.html#Wchar-strings" accesskey="p" rel="prev">Wchar strings</a>, Up: <a href="index.html#Top" accesskey="u" rel="up">Top</a> [<a href="Document-Index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Document-Index.html#Document-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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<hr>
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<a name="Signal-Handling-_0028signal_002eh_0029"></a>
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<h2 class="chapter">7 Signal Handling (<samp>signal.h</samp>)</h2>
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<p>A <em>signal</em> is an event that interrupts the normal flow of control
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in your program. Your operating environment normally defines the full
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set of signals available (see <samp>sys/signal.h</samp>), as well as the
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default means of dealing with them—typically, either printing an
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error message and aborting your program, or ignoring the signal.
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</p>
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<p>All systems support at least the following signals:
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</p><dl compact="compact">
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<dt><code>SIGABRT</code></dt>
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<dd><p>Abnormal termination of a program; raised by the <code>abort</code> function.
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</p>
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</dd>
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<dt><code>SIGFPE</code></dt>
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<dd><p>A domain error in arithmetic, such as overflow, or division by zero.
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</p>
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</dd>
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<dt><code>SIGILL</code></dt>
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<dd><p>Attempt to execute as a function data that is not executable.
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</p>
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</dd>
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<dt><code>SIGINT</code></dt>
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<dd><p>Interrupt; an interactive attention signal.
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</p>
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</dd>
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<dt><code>SIGSEGV</code></dt>
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<dd><p>An attempt to access a memory location that is not available.
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</p>
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</dd>
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<dt><code>SIGTERM</code></dt>
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<dd><p>A request that your program end execution.
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</p></dd>
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</dl>
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<p>Two functions are available for dealing with asynchronous
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signals—one to allow your program to send signals to itself (this is
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called <em>raising</em> a signal), and one to specify subroutines (called
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<em>handlers</em> to handle particular signals that you anticipate may
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occur—whether raised by your own program or the operating environment.
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</p>
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<p>To support these functions, <samp>signal.h</samp> defines three macros:
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</p>
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<dl compact="compact">
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<dt><code>SIG_DFL</code></dt>
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<dd><p>Used with the <code>signal</code> function in place of a pointer to a
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handler subroutine, to select the operating environment’s default
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handling of a signal.
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</p>
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</dd>
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<dt><code>SIG_IGN</code></dt>
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<dd><p>Used with the <code>signal</code> function in place of a pointer to a
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handler, to ignore a particular signal.
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</p>
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</dd>
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<dt><code>SIG_ERR</code></dt>
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<dd><p>Returned by the <code>signal</code> function in place of a pointer to a
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handler, to indicate that your request to set up a handler could not
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be honored for some reason.
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</p></dd>
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</dl>
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<p><samp>signal.h</samp> also defines an integral type, <code>sig_atomic_t</code>.
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This type is not used in any function declarations; it exists only to
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allow your signal handlers to declare a static storage location where
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they may store a signal value. (Static storage is not otherwise
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reliable from signal handlers.)
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</p>
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<table class="menu" border="0" cellspacing="0">
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<tr><td align="left" valign="top">• <a href="psignal.html#psignal" accesskey="1">psignal</a>:</td><td> </td><td align="left" valign="top">Print a signal message to standard error
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</td></tr>
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<tr><td align="left" valign="top">• <a href="raise.html#raise" accesskey="2">raise</a>:</td><td> </td><td align="left" valign="top">Send a signal
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</td></tr>
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<tr><td align="left" valign="top">• <a href="signal.html#signal" accesskey="3">signal</a>:</td><td> </td><td align="left" valign="top">Specify handler subroutine for a signal
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</td></tr>
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</table>
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<hr>
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<div class="header">
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<p>
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Next: <a href="Timefns.html#Timefns" accesskey="n" rel="next">Timefns</a>, Previous: <a href="Wchar-strings.html#Wchar-strings" accesskey="p" rel="prev">Wchar strings</a>, Up: <a href="index.html#Top" accesskey="u" rel="up">Top</a> [<a href="Document-Index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Document-Index.html#Document-Index" title="Index" rel="index">Index</a>]</p>
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