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<title>Issue 957: Various threading bugs #7</title>
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<p><em>This page is a snapshot from the LWG issues list, see the <a href="lwg-active.html">Library Active Issues List</a> for more information and the meaning of <a href="lwg-active.html#C++11">C++11</a> status.</em></p>
<h3 id="957"><a href="lwg-defects.html#957">957</a>. Various threading bugs #7</h3>
<p><b>Section:</b> 30.7.2 <a href="https://wg21.link/time.clock.system">[time.clock.system]</a> <b>Status:</b> <a href="lwg-active.html#C++11">C++11</a>
 <b>Submitter:</b> Pete Becker <b>Opened:</b> 2009-01-07 <b>Last modified:</b> 2016-01-28</p>
<p><b>Priority: </b>Not Prioritized
</p>
<p><b>View all other</b> <a href="lwg-index.html#time.clock.system">issues</a> in [time.clock.system].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#C++11">C++11</a> status.</p>
<p><b>Discussion:</b></p>
<p>
30.7.2 <a href="https://wg21.link/time.clock.system">[time.clock.system]</a>: <code>to_time_t</code> is overspecified. It
requires truncation, but should allow rounding. For example, suppose a
system has a clock that gives times in milliseconds, but <code>time()</code> rounds
those times to the nearest second. Then <code>system_clock</code> can't use any
resolution finer than one second, because if it did, truncating times
between half a second and a full second would produce the wrong <code>time_t</code>
value.
</p>

<p><i>[
Post Summit Anthony Williams provided proposed wording.
]</i></p>


<p><i>[
Batavia (2009-05):
]</i></p>

<blockquote><p>
Move to Review pending input from Howard. and other stakeholders.
</p></blockquote>

<p><i>[
2009-05-23 Howard adds:
]</i></p>


<blockquote><p>
I am in favor of the wording provided by Anthony.
</p></blockquote>

<p><i>[
2009-10 Santa Cruz:
]</i></p>


<blockquote><p>
Move to Ready.
</p></blockquote>



<p id="res-957"><b>Proposed resolution:</b></p>
<p>
In 30.7.2 <a href="https://wg21.link/time.clock.system">[time.clock.system]</a> replace paragraphs 3 and 4 with:
</p>

<blockquote>
<pre>
time_t to_time_t(const time_point&amp; t);
</pre>
<blockquote><p>
-3- <i>Returns:</i> A <code>time_t</code> object that represents the same
point in time as <code>t</code> when both values are <del>truncated</del>
<ins>restricted</ins> to the coarser of the precisions of
<code>time_t</code> and <code>time_point</code>. <ins> It is implementation
defined whether values are rounded or truncated to the required
precision.</ins>
</p></blockquote>

<pre>
time_point from_time_t(time_t t);
</pre>
<blockquote><p>
-4- <i>Returns:</i> A <code>time_point</code> object that represents the
same point in time as <code>t</code> when both values are <del>truncated</del>
<ins>restricted</ins> to the
coarser of the precisions of <code>time_t</code> and <code>time_point</code>.
<ins>It is implementation defined whether values are
rounded or truncated to the required precision.</ins>
</p></blockquote>
</blockquote>





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