144 lines
6.3 KiB
HTML
144 lines
6.3 KiB
HTML
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<title>sigemptyset</title>
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<basefont size="3"> <a name="sigemptyset"></a> <a name="tag_03_684"></a><!-- sigemptyset -->
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<!--header start-->
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<center><font size="2">The Open Group Base Specifications Issue 6<br>
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IEEE Std 1003.1-2001<br>
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Copyright © 2001 The IEEE and The Open Group, All Rights reserved.</font></center>
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<!--header end-->
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<hr size="2" noshade>
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<h4><a name="tag_03_684_01"></a>NAME</h4>
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<blockquote>sigemptyset - initialize and empty a signal set</blockquote>
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<h4><a name="tag_03_684_02"></a>SYNOPSIS</h4>
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<blockquote class="synopsis">
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<div class="box"><code><tt><sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif" alt=
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"[Option Start]" border="0"> #include <<a href="../basedefs/signal.h.html">signal.h</a>><br>
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<br>
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int sigemptyset(sigset_t *</tt><i>set</i><tt>); <img src="../images/opt-end.gif" alt="[Option End]" border="0"></tt></code></div>
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<tt><br>
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</tt></blockquote>
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<h4><a name="tag_03_684_03"></a>DESCRIPTION</h4>
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<blockquote>
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<p>The <i>sigemptyset</i>() function initializes the signal set pointed to by <i>set</i>, such that all signals defined in
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IEEE Std 1003.1-2001 are excluded.</p>
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</blockquote>
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<h4><a name="tag_03_684_04"></a>RETURN VALUE</h4>
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<blockquote>
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<p>Upon successful completion, <i>sigemptyset</i>() shall return 0; otherwise, it shall return -1 and set <i>errno</i> to indicate
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the error.</p>
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</blockquote>
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<h4><a name="tag_03_684_05"></a>ERRORS</h4>
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<blockquote>
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<p>No errors are defined.</p>
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</blockquote>
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<hr>
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<div class="box"><em>The following sections are informative.</em></div>
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<h4><a name="tag_03_684_06"></a>EXAMPLES</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_03_684_07"></a>APPLICATION USAGE</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_03_684_08"></a>RATIONALE</h4>
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<blockquote>
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<p>The implementation of the <i>sigemptyset</i>() (or <a href="../functions/sigfillset.html"><i>sigfillset</i>()</a>) function
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could quite trivially clear (or set) all the bits in the signal set. Alternatively, it would be reasonable to initialize part of
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the structure, such as a version field, to permit binary-compatibility between releases where the size of the set varies. For such
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reasons, either <i>sigemptyset</i>() or <a href="../functions/sigfillset.html"><i>sigfillset</i>()</a> must be called prior to any
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other use of the signal set, even if such use is read-only (for example, as an argument to <a href=
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"../functions/sigpending.html"><i>sigpending</i>()</a>). This function is not intended for dynamic allocation.</p>
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<p>The <a href="../functions/sigfillset.html"><i>sigfillset</i>()</a> and <i>sigemptyset</i>() functions require that the resulting
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signal set include (or exclude) all the signals defined in this volume of IEEE Std 1003.1-2001. Although it is outside
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the scope of this volume of IEEE Std 1003.1-2001 to place this requirement on signals that are implemented as extensions,
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it is recommended that implementation-defined signals also be affected by these functions. However, there may be a good reason for
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a particular signal not to be affected. For example, blocking or ignoring an implementation-defined signal may have undesirable
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side effects, whereas the default action for that signal is harmless. In such a case, it would be preferable for such a signal to
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be excluded from the signal set returned by <a href="../functions/sigfillset.html"><i>sigfillset</i>()</a>.</p>
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<p>In early proposals there was no distinction between invalid and unsupported signals (the names of optional signals that were not
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supported by an implementation were not defined by that implementation). The [EINVAL] error was thus specified as a required error
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for invalid signals. With that distinction, it is not necessary to require implementations of these functions to determine whether
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an optional signal is actually supported, as that could have a significant performance impact for little value. The error could
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have been required for invalid signals and optional for unsupported signals, but this seemed unnecessarily complex. Thus, the error
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is optional in both cases.</p>
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</blockquote>
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<h4><a name="tag_03_684_09"></a>FUTURE DIRECTIONS</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_03_684_10"></a>SEE ALSO</h4>
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<blockquote>
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<p><a href="xsh_chap02_04.html#tag_02_04"><i>Signal Concepts</i></a> , <a href="sigaction.html"><i>sigaction</i>()</a> , <a href=
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"sigaddset.html"><i>sigaddset</i>()</a> , <a href="sigdelset.html"><i>sigdelset</i>()</a> , <a href=
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"sigfillset.html"><i>sigfillset</i>()</a> , <a href="sigismember.html"><i>sigismember</i>()</a> , <a href=
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"sigpending.html"><i>sigpending</i>()</a> , <a href="sigprocmask.html"><i>sigprocmask</i>()</a> , <a href=
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"sigsuspend.html"><i>sigsuspend</i>()</a> , the Base Definitions volume of IEEE Std 1003.1-2001, <a href=
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"../basedefs/signal.h.html"><i><signal.h></i></a></p>
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</blockquote>
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<h4><a name="tag_03_684_11"></a>CHANGE HISTORY</h4>
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<blockquote>
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<p>First released in Issue 3. Included for alignment with the POSIX.1-1988 standard.</p>
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</blockquote>
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<h4><a name="tag_03_684_12"></a>Issue 6</h4>
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<blockquote>
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<p>The SYNOPSIS is marked CX since the presence of this function in the <a href=
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"../basedefs/signal.h.html"><i><signal.h></i></a> header is an extension over the ISO C standard.</p>
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</blockquote>
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<div class="box"><em>End of informative text.</em></div>
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