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<title>Issue 3962: What is the "decimal precision of the input"?</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#New">New</a> status.</em></p>
<h3 id="3962"><a href="lwg-active.html#3962">3962</a>. What is the "decimal precision of the input"?</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#New">New</a>
 <b>Submitter:</b> Jonathan Wakely <b>Opened:</b> 2023-07-28 <b>Last modified:</b> 2024-01-29</p>
<p><b>Priority: </b>3
</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#New">New</a> status.</p>
<p><b>Discussion:</b></p>
<p>
The <code>%j</code> flag talks about "the type being parsed" and <code>%S</code> talks about
"the input time" and "the input", but doesn't really define which types
those are.
</p>

<p><i>[2023-11-02; Reflector poll]</i></p>

<p>
Set priority to 3 after reflector poll.
</p>



<p id="res-3962"><b>Proposed resolution:</b></p>
<p>
This wording is relative to <a href="https://wg21.link/N4950" title=" Working Draft, Standard for Programming Language C++">N4950</a>.
</p>

<ol>

<li><p>Modify 30.13 <a href="https://wg21.link/time.parse">[time.parse]</a> as indicated:</p>

<blockquote>
<p>
<ins>
-?-
In Table 102 the type <code>Parsable</code> denotes the type of the second
argument to <code>from_stream</code>.
</ins>
</p>

<table>
<tr><td><code style="padding:3em; text-align: center">%j</code></td>
<td>
If <del>the type being parsed</del> <ins><code>Parsable</code></ins>
is a specialization of <code>duration</code>, a decimal number of days.
</td></tr>
<tr><td>&nbsp;</td><td></td></tr>
<tr><td><code style="padding:3em; text-align: center">%S</code></td>
<td>
The seconds as a decimal number.
The modified command <code>%<i>N</i>S</code> specifies the maximum number of
characters to read.
If <code><i>N</i></code> is not specified, the default is 2
<ins>if <code>Parsable</code> is a calendrical type (30.8 <a href="https://wg21.link/time.cal">[time.cal]</a>)</ins>
<del>if the input time has a precision convertible to seconds</del>.
Otherwise the default width is determined by the decimal precision of
<del>the input</del> <ins><code>Parsable</code>,
determined in the same manner as <code>hh_mm_ss::fractional_width</code>
(30.9 <a href="https://wg21.link/time.hms">[time.hms]</a>). If the number of fractional decimal digits for
the type is zero, then the default for <code><i>N</i></code> is 2. Otherwise, it is
3 + W, where W is the number of fractional decimal digits.
If <code><i>N</i></code> is less than 3, the field is interpreted as a decimal integer, 
otherwise </ins><del>and</del>
the field is interpreted as a <code>long double</code> in a fixed format.
If encountered, the locale determines the decimal point character.
Leading zeroes are permitted but not required.
The modified command <code>%OS</code> interprets the locale's alternative
representation.
</td></tr>
</table>

</blockquote>
</li>
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