Skip to content

Commit e8c65b8

Browse files
author
github-actions
committed
Automatic update from GitHub Actions workflow
1 parent 49043f3 commit e8c65b8

22 files changed

+316
-41
lines changed

‎issue4285.html‎

Lines changed: 105 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,105 @@
1+
<!DOCTYPE html>
2+
<html lang="en">
3+
<head>
4+
<meta charset="utf-8">
5+
<title>Issue 4285: time_get::do_get_date is problematic even after LWG 461</title>
6+
<meta property="og:title" content="Issue 4285: time_get::do_get_date is problematic even after LWG 461">
7+
<meta property="og:description" content="C++ library issue. Status: New">
8+
<meta property="og:url" content="https://cplusplus.github.io/LWG/issue4285.html">
9+
<meta property="og:type" content="website">
10+
<meta property="og:image" content="http://cplusplus.github.io/LWG/images/cpp_logo.png">
11+
<meta property="og:image:alt" content="C++ logo">
12+
<style>
13+
p {text-align:justify}
14+
li {text-align:justify}
15+
pre code.backtick::before { content: "`" }
16+
pre code.backtick::after { content: "`" }
17+
blockquote.note
18+
{
19+
background-color:#E0E0E0;
20+
padding-left: 15px;
21+
padding-right: 15px;
22+
padding-top: 1px;
23+
padding-bottom: 1px;
24+
}
25+
ins {background-color:#A0FFA0}
26+
del {background-color:#FFA0A0}
27+
table.issues-index { border: 1px solid; border-collapse: collapse; }
28+
table.issues-index th { text-align: center; padding: 4px; border: 1px solid; }
29+
table.issues-index td { padding: 4px; border: 1px solid; }
30+
table.issues-index td:nth-child(1) { text-align: right; }
31+
table.issues-index td:nth-child(2) { text-align: left; }
32+
table.issues-index td:nth-child(3) { text-align: left; }
33+
table.issues-index td:nth-child(4) { text-align: left; }
34+
table.issues-index td:nth-child(5) { text-align: center; }
35+
table.issues-index td:nth-child(6) { text-align: center; }
36+
table.issues-index td:nth-child(7) { text-align: left; }
37+
table.issues-index td:nth-child(5) span.no-pr { color: red; }
38+
@media (prefers-color-scheme: dark) {
39+
html {
40+
color: #ddd;
41+
background-color: black;
42+
}
43+
ins {
44+
background-color: #225522
45+
}
46+
del {
47+
background-color: #662222
48+
}
49+
a {
50+
color: #6af
51+
}
52+
a:visited {
53+
color: #6af
54+
}
55+
blockquote.note
56+
{
57+
background-color: rgba(255, 255, 255, .10)
58+
}
59+
}
60+
</style>
61+
</head>
62+
<body>
63+
<hr>
64+
<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>
65+
<h3 id="4285"><a href="lwg-active.html#4285">4285</a>. <code class='backtick'>time_get::do_get_date</code> is problematic even after LWG 461</h3>
66+
<p><b>Section:</b> 28.3.4.6.2.2 <a href="https://wg21.link/locale.time.get.members">[locale.time.get.members]</a> <b>Status:</b> <a href="lwg-active.html#New">New</a>
67+
<b>Submitter:</b> S. B. Tam <b>Opened:</b> 2025-06-27 <b>Last modified:</b> 2025-06-28</p>
68+
<p><b>Priority: </b>Not Prioritized
69+
</p>
70+
<p><b>View all issues with</b> <a href="lwg-status.html#New">New</a> status.</p>
71+
<p><b>Discussion:</b></p>
72+
<p>
73+
Background: <a href="https://github.com/cplusplus/draft/pull/8009">https://github.com/cplusplus/draft/pull/8009</a>
74+
<p/>
75+
LWG <a href="lwg-defects.html#461" title="time_get hard or impossible to implement (Status: CD1)">461</a><sup><a href="https://cplusplus.github.io/LWG/issue461" title="Latest snapshot">(i)</a></sup> changed <code class='backtick'>time_get::do_get_date</code> to parse a set of fixed formats. For example, if
76+
<code class='backtick'>time_get::date_order()</code> is <code class='backtick'>no_order</code> or <code class='backtick'>mdy</code>, the format parsed by <code class='backtick'>do_get_date</code> is <code class='backtick'>%m/%d/%y</code>.
77+
<p/>
78+
This has several problems:
79+
</p>
80+
<ol>
81+
<li><p>When the resolution of LWG <a href="lwg-defects.html#461" title="time_get hard or impossible to implement (Status: CD1)">461</a><sup><a href="https://cplusplus.github.io/LWG/issue461" title="Latest snapshot">(i)</a></sup> was applied to the draft standard, the slashes were lost.
82+
This could mislead people into implementing <code class='backtick'>do_get_date</code> using the incorrect formats. Fortunately, none
83+
of the standard library implementations are affected by this mistake.</p></li>
84+
<li><p>Only 2-digit years are accepted due to the use of <code class='backtick'>%y</code>. This could lead to incorrect parse if
85+
<code class='backtick'>strftime</code> uses <code class='backtick'>%Y</code> for the locale's date format.</p></li>
86+
<li><p><code class='backtick'>date_order()</code> might need additional locale facets to find out the date order, but it doesn't have an
87+
<code>ios_base&amp;</code> argument from which to get the locale.</p></li>
88+
<li><p>Many locales do not use any of the specified formats. For example, <code class='backtick'>de_DE</code> uses <code class='backtick'>%d.%m.%Y</code>, <code class='backtick'>zh_CN</code>
89+
uses <code class='backtick'>%Y?%m?%d?</code>. Although 28.3.4.6.2.3 <a href="https://wg21.link/locale.time.get.virtuals">[locale.time.get.virtuals]</a>/5 gives an implementation the latitude
90+
to accept additional formats, ambiguity could arise if the locale's format disagrees with <code class='backtick'>date_order()</code>.</p></li>
91+
</ol>
92+
<p>
93+
On POSIX systems, it is possible to query the locale's date format using <code class='backtick'>nl_langinfo(D_FMT)</code>.
94+
Maybe an implementation should be allowed to use that format <b>instead</b> of the one indicated by <code class='backtick'>date_order()</code>.
95+
</p>
96+
97+
98+
<p id="res-4285"><b>Proposed resolution:</b></p>
99+
100+
101+
102+
103+
104+
</body>
105+
</html>

0 commit comments

Comments
 (0)