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<h4 class="subsection">24.3.4 <code>sigaction</code> Function Example</h4>

<p>In <a href="Basic-Signal-Handling.html#Basic-Signal-Handling">Basic Signal Handling</a>, we gave an example of establishing a
simple handler for termination signals using <code>signal</code>.  Here is an
equivalent example using <code>sigaction</code>:

<pre class="smallexample">     #include &lt;signal.h&gt;
     
     void
     termination_handler (int signum)
     {
       struct temp_file *p;
     
       for (p = temp_file_list; p; p = p-&gt;next)
         unlink (p-&gt;name);
     }
     
     int
     main (void)
     {
       ...
       struct sigaction new_action, old_action;
     
       /* <span class="roman">Set up the structure to specify the new action.</span> */
       new_action.sa_handler = termination_handler;
       sigemptyset (&amp;new_action.sa_mask);
       new_action.sa_flags = 0;
     
       sigaction (SIGINT, NULL, &amp;old_action);
       if (old_action.sa_handler != SIG_IGN)
         sigaction (SIGINT, &amp;new_action, NULL);
       sigaction (SIGHUP, NULL, &amp;old_action);
       if (old_action.sa_handler != SIG_IGN)
         sigaction (SIGHUP, &amp;new_action, NULL);
       sigaction (SIGTERM, NULL, &amp;old_action);
       if (old_action.sa_handler != SIG_IGN)
         sigaction (SIGTERM, &amp;new_action, NULL);
       ...
     }
</pre>
   <p>The program just loads the <code>new_action</code> structure with the desired
parameters and passes it in the <code>sigaction</code> call.  The usage of
<code>sigemptyset</code> is described later; see <a href="Blocking-Signals.html#Blocking-Signals">Blocking Signals</a>.

   <p>As in the example using <code>signal</code>, we avoid handling signals
previously set to be ignored.  Here we can avoid altering the signal
handler even momentarily, by using the feature of <code>sigaction</code> that
lets us examine the current action without specifying a new one.

   <p>Here is another example.  It retrieves information about the current
action for <code>SIGINT</code> without changing that action.

<pre class="smallexample">     struct sigaction query_action;
     
     if (sigaction (SIGINT, NULL, &amp;query_action) &lt; 0)
       /* <code>sigaction</code><span class="roman"> returns -1 in case of error.</span> */
     else if (query_action.sa_handler == SIG_DFL)
       /* <code>SIGINT</code><span class="roman"> is handled in the default, fatal manner.</span> */
     else if (query_action.sa_handler == SIG_IGN)
       /* <code>SIGINT</code><span class="roman"> is ignored.</span> */
     else
       /* <span class="roman">A programmer-defined signal handler is in effect.</span> */
</pre>
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