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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 <signal.h> |
| |
| void |
| termination_handler (int signum) |
| { |
| struct temp_file *p; |
| |
| for (p = temp_file_list; p; p = p->next) |
| unlink (p->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 (&new_action.sa_mask); |
| new_action.sa_flags = 0; |
| |
| sigaction (SIGINT, NULL, &old_action); |
| if (old_action.sa_handler != SIG_IGN) |
| sigaction (SIGINT, &new_action, NULL); |
| sigaction (SIGHUP, NULL, &old_action); |
| if (old_action.sa_handler != SIG_IGN) |
| sigaction (SIGHUP, &new_action, NULL); |
| sigaction (SIGTERM, NULL, &old_action); |
| if (old_action.sa_handler != SIG_IGN) |
| sigaction (SIGTERM, &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, &query_action) < 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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