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| <h4 class="subsection">24.3.3 Interaction of <code>signal</code> and <code>sigaction</code></h4> |
| |
| <p>It's possible to use both the <code>signal</code> and <code>sigaction</code> |
| functions within a single program, but you have to be careful because |
| they can interact in slightly strange ways. |
| |
| <p>The <code>sigaction</code> function specifies more information than the |
| <code>signal</code> function, so the return value from <code>signal</code> cannot |
| express the full range of <code>sigaction</code> possibilities. Therefore, if |
| you use <code>signal</code> to save and later reestablish an action, it may |
| not be able to reestablish properly a handler that was established with |
| <code>sigaction</code>. |
| |
| <p>To avoid having problems as a result, always use <code>sigaction</code> to |
| save and restore a handler if your program uses <code>sigaction</code> at all. |
| Since <code>sigaction</code> is more general, it can properly save and |
| reestablish any action, regardless of whether it was established |
| originally with <code>signal</code> or <code>sigaction</code>. |
| |
| <p>On some systems if you establish an action with <code>signal</code> and then |
| examine it with <code>sigaction</code>, the handler address that you get may |
| not be the same as what you specified with <code>signal</code>. It may not |
| even be suitable for use as an action argument with <code>signal</code>. But |
| you can rely on using it as an argument to <code>sigaction</code>. This |
| problem never happens on the GNU system. |
| |
| <p>So, you're better off using one or the other of the mechanisms |
| consistently within a single program. |
| |
| <p><strong>Portability Note:</strong> The basic <code>signal</code> function is a feature |
| of ISO C<!-- /@w -->, while <code>sigaction</code> is part of the POSIX.1 standard. If |
| you are concerned about portability to non-POSIX systems, then you |
| should use the <code>signal</code> function instead. |
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