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<title>Issue 3218: Modifier for %d parse flag does not match POSIX and format specification</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++20">C++20</a> status.</em></p>
<h3 id="3218"><a href="lwg-defects.html#3218">3218</a>. Modifier for <code>%d</code> parse flag does not match POSIX and <code>format</code> specification</h3>
<p><b>Section:</b> 30.13 <a href="https://wg21.link/time.parse">[time.parse]</a> <b>Status:</b> <a href="lwg-active.html#C++20">C++20</a>
 <b>Submitter:</b> Tomasz Kami&nacute;ski <b>Opened:</b> 2019-06-13 <b>Last modified:</b> 2021-02-25</p>
<p><b>Priority: </b>0
</p>
<p><b>View other</b> <a href="lwg-index-open.html#time.parse">active issues</a> in [time.parse].</p>
<p><b>View all other</b> <a href="lwg-index.html#time.parse">issues</a> in [time.parse].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#C++20">C++20</a> status.</p>
<p><b>Discussion:</b></p>
<p>
Currently, the '<code>%d</code>' parse flags accepts the '<code>E</code>' modifier to parse the
locale's alternative representation, see Table 88 &mdash;
<a href="http://eel.is/c++draft/time.parse#11.sentence-26">
"Meaning of <code>parse</code> flags"</a>:
</p>
<blockquote><p>
The modified command <code>%Ed</code> interprets the locale's
alternative representation of the day of the month.
</p></blockquote>
<p>
This is inconsistent with the
<a href="http://pubs.opengroup.org/onlinepubs/9699919799/functions/strftime.html">POSIX
<code>strftime</code> specification</a> and the <code>format</code> functions, that uses '<code>O</code>'
to output alternate locale representation. Per Table 87 &mdash;
<a href="http://eel.is/c++draft/time.format#17.sentence-28">"Meaning of <code>format</code>
conversion specifiers"</a>:
</p>
<blockquote><p>
The modified command <code>%Od</code> produces the locale's alternative representation.
</p></blockquote>

<p><i>[2019-06-24; Howard comments]</i></p>

<p>
This was simply a type-o in my documentation that infected the proposal and subsequently the C++ working draft.
<p/>
None of <code>std::time_put</code>, C's <code>strftime</code>, or POSIX's <code>strftime</code> support
<code>%Ed</code> but all support <code>%Od</code>. Furthermore the existing example implementation
supports <code>%Od</code> but not <code>%Ed</code>. And all the existing example implementation
does is forward to <code>std::time_put</code>.
</p>

<p><i>[2019-07 Issue Prioritization]</i></p>

<p>Status to Tentatively Ready after five positive votes on the reflector.</p>


<p id="res-3218"><b>Proposed resolution:</b></p>
<p>This wording is relative to <a href="https://wg21.link/n4810">N4810</a>.</p>

<ol>
<li><p>Modify 30.13 <a href="https://wg21.link/time.parse">[time.parse]</a>, Table 88 &mdash; "Meaning of <code>parse</code> flags",
as indicated:</p>

<blockquote>

<table border="1">
<caption>Table 88 &mdash; Meaning of <code>parse</code> flags</caption>
<tr style="text-align:center">
<th>Flag</th>
<th>Parsed value</th>
</tr>
<tr>
<td colspan="3" align="center">
<code>[&hellip;]</code>
</td>
</tr>
<tr>
<td><code>%d</code></td>
<td>The day of the month as a decimal number. The modified command <code>%<i>N</i>d</code>
specifies the maximum number of characters to read. If <code><i>N</i></code> is not specified,
the default is 2. Leading zeroes are permitted but not required. The modified command
<code>%<del>E</del><ins>O</ins>d</code> interprets the locale's alternative representation
of the day of the month.</td>
</tr>
<tr>
<td colspan="3" align="center">
<code>[&hellip;]</code>
</td>
</tr>
</table>

</blockquote>
</li>
</ol>




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