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<title>posix_trace_getnext_event</title>
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<basefont size="3"> <a name="posix_trace_getnext_event"></a> <a name="tag_03_472"></a><!-- posix_trace_getnext_event -->
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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_472_01"></a>NAME</h4>
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<blockquote>posix_trace_getnext_event, posix_trace_timedgetnext_event, posix_trace_trygetnext_event - retrieve a trace event
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(<b>TRACING</b>)</blockquote>
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<h4><a name="tag_03_472_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('TRC')">TRC</a>]</sup> <img src="../images/opt-start.gif" alt=
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"[Option Start]" border="0"> #include <<a href="../basedefs/sys/types.h.html">sys/types.h</a>><br>
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#include <<a href="../basedefs/trace.h.html">trace.h</a>><br>
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<br>
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int posix_trace_getnext_event(trace_id_t</tt> <i>trid</i><tt>,<br>
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struct posix_trace_event_info *restrict</tt> <i>event</i><tt>,<br>
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void *restrict</tt> <i>data</i><tt>, size_t</tt> <i>num_bytes</i><tt>,<br>
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size_t *restrict</tt> <i>data_len</i><tt>, int *restrict</tt> <i>unavailable</i><tt>);<br>
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<img src="../images/opt-end.gif" alt="[Option End]" border="0"></tt></code></div>
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<div class="box"><code><tt><sup>[<a href="javascript:open_code('TRC TMO')">TRC TMO</a>]</sup> <img src="../images/opt-start.gif" alt=
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"[Option Start]" border="0"> int posix_trace_timedgetnext_event(trace_id_t</tt> <i>trid</i><tt>,<br>
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struct posix_trace_event_info *restrict</tt> <i>event</i><tt>,<br>
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void *restrict</tt> <i>data</i><tt>, size_t</tt> <i>num_bytes</i><tt>,<br>
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size_t *restrict</tt> <i>data_len</i><tt>, int *restrict</tt> <i>unavailable</i><tt>,<br>
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const struct timespec *restrict</tt> <i>abs_timeout</i><tt>);<br>
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<img src="../images/opt-end.gif" alt="[Option End]" border="0"></tt></code></div>
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<div class="box"><code><tt><sup>[<a href="javascript:open_code('TRC')">TRC</a>]</sup> <img src="../images/opt-start.gif" alt=
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"[Option Start]" border="0"> int posix_trace_trygetnext_event(trace_id_t</tt> <i>trid</i><tt>,<br>
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struct posix_trace_event_info *restrict</tt> <i>event</i><tt>,<br>
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void *restrict</tt> <i>data</i><tt>, size_t</tt> <i>num_bytes</i><tt>,<br>
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size_t *restrict</tt> <i>data_len</i><tt>, int *restrict</tt> <i>unavailable</i><tt>); <img
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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_472_03"></a>DESCRIPTION</h4>
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<blockquote>
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<p>The <i>posix_trace_getnext_event</i>() function shall report a recorded trace event either from an active trace stream without
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log <sup>[<a href="javascript:open_code('TRL')">TRL</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">
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or a pre-recorded trace stream identified by the <i>trid</i> argument. <img src="../images/opt-end.gif" alt="[Option End]"
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border="0"> The <i>posix_trace_trygetnext_event</i>() function shall report a recorded trace event from an active trace stream
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without log identified by the <i>trid</i> argument.</p>
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<p>The trace event information associated with the recorded trace event shall be copied by the function into the structure pointed
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to by the argument <i>event</i> and the data associated with the trace event shall be copied into the buffer pointed to by the
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<i>data</i> argument.</p>
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<p>The <i>posix_trace_getnext_event</i>() function shall block if the <i>trid</i> argument identifies an active trace stream and
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there is currently no trace event ready to be retrieved. When returning, if a recorded trace event was reported, the variable
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pointed to by the <i>unavailable</i> argument shall be set to zero. Otherwise, the variable pointed to by the <i>unavailable</i>
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argument shall be set to a value different from zero.</p>
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<p><sup>[<a href="javascript:open_code('TMO')">TMO</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">
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The <i>posix_trace_timedgetnext_event</i>() function shall attempt to get another trace event from an active trace stream
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without log, as in the <i>posix_trace_getnext_event</i>() function. However, if no trace event is available from the trace stream,
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the implied wait shall be terminated when the timeout specified by the argument <i>abs_timeout</i> expires, and the function shall
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return the error [ETIMEDOUT].</p>
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<p>The timeout shall expire when the absolute time specified by <i>abs_timeout</i> passes, as measured by the clock upon which
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timeouts are based (that is, when the value of that clock equals or exceeds <i>abs_timeout</i>), or if the absolute time specified
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by <i>abs_timeout</i> has already passed at the time of the call. <img src="../images/opt-end.gif" alt="[Option End]" border=
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"0"></p>
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<p><sup>[<a href="javascript:open_code('TMO TMR')">TMO TMR</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]"
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border="0"> If the Timers option is supported, the timeout shall be based on the CLOCK_REALTIME clock; if the Timers option
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is not supported, the timeout shall be based on the system clock as returned by the <a href=
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"../functions/time.html"><i>time</i>()</a> function. The resolution of the timeout shall be the resolution of the clock on which it
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is based. The <b>timespec</b> data type is defined in the <a href="../basedefs/time.h.html"><i><time.h></i></a> header. <img
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src="../images/opt-end.gif" alt="[Option End]" border="0"></p>
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<p><sup>[<a href="javascript:open_code('TMO')">TMO</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">
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Under no circumstance shall the function fail with a timeout if a trace event is immediately available from the trace stream. The
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validity of the <i>abs_timeout</i> argument need not be checked if a trace event is immediately available from the trace
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stream.</p>
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<p>The behavior of this function for a pre-recorded trace stream is unspecified. <img src="../images/opt-end.gif" alt=
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"[Option End]" border="0"></p>
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<p>The <i>posix_trace_trygetnext_event</i>() function shall not block. <sup>[<a href="javascript:open_code('TRL')">TRL</a>]</sup>
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<img src="../images/opt-start.gif" alt="[Option Start]" border="0"> This function shall return an error if the <i>trid</i>
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argument identifies a pre-recorded trace stream. <img src="../images/opt-end.gif" alt="[Option End]" border="0"> If a recorded
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trace event was reported, the variable pointed to by the <i>unavailable</i> argument shall be set to zero. Otherwise, if no trace
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event was reported, the variable pointed to by the <i>unavailable</i> argument shall be set to a value different from zero.</p>
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<p>The argument <i>num_bytes</i> shall be the size of the buffer pointed to by the <i>data</i> argument. The argument
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<i>data_len</i> reports to the application the length in bytes of the data record just transferred. If <i>num_bytes</i> is greater
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than or equal to the size of the data associated with the trace event pointed to by the <i>event</i> argument, all the recorded
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data shall be transferred. In this case, the <i>truncation-status</i> member of the trace event structure shall be either
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POSIX_TRACE_NOT_TRUNCATED, if the trace event data was recorded without truncation while tracing, or POSIX_TRACE_TRUNCATED_RECORD,
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if the trace event data was truncated when it was recorded. If the <i>num_bytes</i> argument is less than the length of recorded
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trace event data, the data transferred shall be truncated to a length of <i>num_bytes</i>, the value stored in the variable pointed
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to by <i>data_len</i> shall be equal to <i>num_bytes</i>, and the <i>truncation-status</i> member of the <i>event</i> structure
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argument shall be set to POSIX_TRACE_TRUNCATED_READ (see the <b>posix_trace_event_info</b> structure defined in <a href=
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"../basedefs/trace.h.html"><i><trace.h></i></a>).</p>
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<p>The report of a trace event shall be sequential starting from the oldest recorded trace event. Trace events shall be reported in
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the order in which they were generated, up to an implementation-defined time resolution that causes the ordering of trace events
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occurring very close to each other to be unknown. Once reported, a trace event cannot be reported again from an active trace
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stream. Once a trace event is reported from an active trace stream without log, the trace stream shall make the resources
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associated with that trace event available to record future generated trace events.</p>
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</blockquote>
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<h4><a name="tag_03_472_04"></a>RETURN VALUE</h4>
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<blockquote>
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<p>Upon successful completion, these functions shall return a value of zero. Otherwise, they shall return the corresponding error
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number.</p>
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<p>If successful, these functions store:</p>
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<ul>
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<li>
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<p>The recorded trace event in the object pointed to by <i>event</i></p>
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</li>
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<li>
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<p>The trace event information associated with the recorded trace event in the object pointed to by <i>data</i></p>
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</li>
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<li>
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<p>The length of this trace event information in the object pointed to by <i>data_len</i></p>
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</li>
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<li>
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<p>The value of zero in the object pointed to by <i>unavailable</i></p>
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</li>
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</ul>
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</blockquote>
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<h4><a name="tag_03_472_05"></a>ERRORS</h4>
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<blockquote>
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<p>These functions shall fail if:</p>
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<dl compact>
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<dt>[EINVAL]</dt>
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<dd>The trace stream identifier argument <i>trid</i> is invalid.</dd>
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</dl>
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<p>The <i>posix_trace_getnext_event</i>() and <i>posix_trace_timedgetnext_event</i>() functions shall fail if:</p>
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<dl compact>
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<dt>[EINTR]</dt>
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<dd>The operation was interrupted by a signal, and so the call had no effect.</dd>
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</dl>
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<p>The <i>posix_trace_trygetnext_event</i>() function shall fail if:</p>
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<dl compact>
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<dt>[EINVAL]</dt>
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<dd>The trace stream identifier argument <i>trid</i> does not correspond to an active trace stream.</dd>
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</dl>
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<p><sup>[<a href="javascript:open_code('TMO')">TMO</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">
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The <i>posix_trace_timedgetnext_event</i>() function shall fail if:</p>
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<dl compact>
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<dt>[EINVAL]</dt>
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<dd>There is no trace event immediately available from the trace stream, and the <i>timeout</i> argument is invalid.</dd>
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<dt>[ETIMEDOUT]</dt>
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<dd>No trace event was available from the trace stream before the specified timeout <i>timeout</i> expired.</dd>
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</dl>
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<img src="../images/opt-end.gif" alt="[Option End]" border="0"></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_472_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_472_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_472_08"></a>RATIONALE</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_472_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_472_10"></a>SEE ALSO</h4>
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<blockquote>
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<p><a href="posix_trace_create.html"><i>posix_trace_create</i>()</a> , <a href=
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"posix_trace_open.html"><i>posix_trace_open</i>()</a> , the Base Definitions volume of IEEE Std 1003.1-2001, <a href=
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"../basedefs/sys/types.h.html"><i><sys/types.h></i></a>, <a href="../basedefs/trace.h.html"><i><trace.h></i></a></p>
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</blockquote>
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<h4><a name="tag_03_472_11"></a>CHANGE HISTORY</h4>
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<blockquote>
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<p>First released in Issue 6. Derived from IEEE Std 1003.1q-2000.</p>
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<p>IEEE PASC Interpretation 1003.1 #123 is applied.</p>
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</blockquote>
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<div class="box"><em>End of informative text.</em></div>
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