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| <h4 class="subsection">24.7.2 Signal Sets</h4> |
| |
| <p>All of the signal blocking functions use a data structure called a |
| <dfn>signal set</dfn> to specify what signals are affected. Thus, every |
| activity involves two stages: creating the signal set, and then passing |
| it as an argument to a library function. |
| <a name="index-signal-set-2957"></a> |
| These facilities are declared in the header file <samp><span class="file">signal.h</span></samp>. |
| <a name="index-signal_002eh-2958"></a> |
| <!-- signal.h --> |
| <!-- POSIX.1 --> |
| |
| <div class="defun"> |
| — Data Type: <b>sigset_t</b><var><a name="index-sigset_005ft-2959"></a></var><br> |
| <blockquote><p>The <code>sigset_t</code> data type is used to represent a signal set. |
| Internally, it may be implemented as either an integer or structure |
| type. |
| |
| <p>For portability, use only the functions described in this section to |
| initialize, change, and retrieve information from <code>sigset_t</code> |
| objects—don't try to manipulate them directly. |
| </p></blockquote></div> |
| |
| <p>There are two ways to initialize a signal set. You can initially |
| specify it to be empty with <code>sigemptyset</code> and then add specified |
| signals individually. Or you can specify it to be full with |
| <code>sigfillset</code> and then delete specified signals individually. |
| |
| <p>You must always initialize the signal set with one of these two |
| functions before using it in any other way. Don't try to set all the |
| signals explicitly because the <code>sigset_t</code> object might include some |
| other information (like a version field) that needs to be initialized as |
| well. (In addition, it's not wise to put into your program an |
| assumption that the system has no signals aside from the ones you know |
| about.) |
| |
| <!-- signal.h --> |
| <!-- POSIX.1 --> |
| <div class="defun"> |
| — Function: int <b>sigemptyset</b> (<var>sigset_t *set</var>)<var><a name="index-sigemptyset-2960"></a></var><br> |
| <blockquote><p>This function initializes the signal set <var>set</var> to exclude all of the |
| defined signals. It always returns <code>0</code>. |
| </p></blockquote></div> |
| |
| <!-- signal.h --> |
| <!-- POSIX.1 --> |
| <div class="defun"> |
| — Function: int <b>sigfillset</b> (<var>sigset_t *set</var>)<var><a name="index-sigfillset-2961"></a></var><br> |
| <blockquote><p>This function initializes the signal set <var>set</var> to include |
| all of the defined signals. Again, the return value is <code>0</code>. |
| </p></blockquote></div> |
| |
| <!-- signal.h --> |
| <!-- POSIX.1 --> |
| <div class="defun"> |
| — Function: int <b>sigaddset</b> (<var>sigset_t *set, int signum</var>)<var><a name="index-sigaddset-2962"></a></var><br> |
| <blockquote><p>This function adds the signal <var>signum</var> to the signal set <var>set</var>. |
| All <code>sigaddset</code> does is modify <var>set</var>; it does not block or |
| unblock any signals. |
| |
| <p>The return value is <code>0</code> on success and <code>-1</code> on failure. |
| The following <code>errno</code> error condition is defined for this function: |
| |
| <dl> |
| <dt><code>EINVAL</code><dd>The <var>signum</var> argument doesn't specify a valid signal. |
| </dl> |
| </p></blockquote></div> |
| |
| <!-- signal.h --> |
| <!-- POSIX.1 --> |
| <div class="defun"> |
| — Function: int <b>sigdelset</b> (<var>sigset_t *set, int signum</var>)<var><a name="index-sigdelset-2963"></a></var><br> |
| <blockquote><p>This function removes the signal <var>signum</var> from the signal set |
| <var>set</var>. All <code>sigdelset</code> does is modify <var>set</var>; it does not |
| block or unblock any signals. The return value and error conditions are |
| the same as for <code>sigaddset</code>. |
| </p></blockquote></div> |
| |
| <p>Finally, there is a function to test what signals are in a signal set: |
| |
| <!-- signal.h --> |
| <!-- POSIX.1 --> |
| <div class="defun"> |
| — Function: int <b>sigismember</b> (<var>const sigset_t *set, int signum</var>)<var><a name="index-sigismember-2964"></a></var><br> |
| <blockquote><p>The <code>sigismember</code> function tests whether the signal <var>signum</var> is |
| a member of the signal set <var>set</var>. It returns <code>1</code> if the signal |
| is in the set, <code>0</code> if not, and <code>-1</code> if there is an error. |
| |
| <p>The following <code>errno</code> error condition is defined for this function: |
| |
| <dl> |
| <dt><code>EINVAL</code><dd>The <var>signum</var> argument doesn't specify a valid signal. |
| </dl> |
| </p></blockquote></div> |
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