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<a name="signal_002d_002d_002dspecify-handler-subroutine-for-a-signal"></a>
<h3 class="section">7.3 <code>signal</code>&mdash;specify handler subroutine for a signal</h3>
<a name="index-signal"></a>
<a name="index-_005fsignal_005fr"></a>
<p><strong>Synopsis</strong>
</p><div class="example">
<pre class="example">#include &lt;signal.h&gt;
void (*signal(int <var>sig</var>, void(*<var>func</var>)(int))) (int);

void (*_signal_r(void *<var>reent</var>, int <var>sig</var>, void(*<var>func</var>)(int))) (int);

</pre></div>
<p><strong>Description</strong><br>
<code>signal</code> provides a simple signal-handling implementation for embedded
targets.
</p>
<p><code>signal</code> allows you to request changed treatment for a particular
signal <var>sig</var>.  You can use one of the predefined macros <code>SIG_DFL</code>
(select system default handling) or <code>SIG_IGN</code> (ignore this signal)
as the value of <var>func</var>; otherwise, <var>func</var> is a function pointer
that identifies a subroutine in your program as the handler for this signal.
</p>
<p>Some of the execution environment for signal handlers is
unpredictable; notably, the only library function required to work
correctly from within a signal handler is <code>signal</code> itself, and
only when used to redefine the handler for the current signal value.
</p>
<p>Static storage is likewise unreliable for signal handlers, with one
exception: if you declare a static storage location as &lsquo;<code>volatile
sig_atomic_t</code>&rsquo;, then you may use that location in a signal handler to
store signal values.
</p>
<p>If your signal handler terminates using <code>return</code> (or implicit
return), your program&rsquo;s execution continues at the point
where it was when the signal was raised (whether by your program
itself, or by an external event).  Signal handlers can also
use functions such as <code>exit</code> and <code>abort</code> to avoid returning.
</p>
<p>The alternate function <code>_signal_r</code> is the reentrant version.
The extra argument <var>reent</var> is a pointer to a reentrancy structure.
</p>

<br>
<p><strong>Returns</strong><br>
If your request for a signal handler cannot be honored, the result is
<code>SIG_ERR</code>; a specific error number is also recorded in <code>errno</code>.
</p>
<p>Otherwise, the result is the previous handler (a function pointer or
one of the predefined macros).
</p>
<br>
<p><strong>Portability</strong><br>
ANSI C requires <code>signal</code>.
</p>
<p>No supporting OS subroutines are required to link with <code>signal</code>, but
it will not have any useful effects, except for software generated signals,
without an operating system that can actually raise exceptions.
</p>
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