<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>Issue 2637: [filesys.ts] [PDTS] All functions with error_code arguments should be noexcept</title>
<meta property="og:title" content="Issue 2637: [filesys.ts] [PDTS] All functions with error_code arguments should be noexcept">
<meta property="og:description" content="C++ library issue. Status: TS">
<meta property="og:url" content="https://cplusplus.github.io/LWG/issue2637.html">
<meta property="og:type" content="website">
<meta property="og:image" content="http://cplusplus.github.io/LWG/images/cpp_logo.png">
<meta property="og:image:alt" content="C++ logo">
<style>
  p {text-align:justify}
  li {text-align:justify}
  pre code.backtick::before { content: "`" }
  pre code.backtick::after { content: "`" }
  blockquote.note
  {
    background-color:#E0E0E0;
    padding-left: 15px;
    padding-right: 15px;
    padding-top: 1px;
    padding-bottom: 1px;
  }
  ins {background-color:#A0FFA0}
  del {background-color:#FFA0A0}
  table.issues-index { border: 1px solid; border-collapse: collapse; }
  table.issues-index th { text-align: center; padding: 4px; border: 1px solid; }
  table.issues-index td { padding: 4px; border: 1px solid; }
  table.issues-index td:nth-child(1) { text-align: right; }
  table.issues-index td:nth-child(2) { text-align: left; }
  table.issues-index td:nth-child(3) { text-align: left; }
  table.issues-index td:nth-child(4) { text-align: left; }
  table.issues-index td:nth-child(5) { text-align: center; }
  table.issues-index td:nth-child(6) { text-align: center; }
  table.issues-index td:nth-child(7) { text-align: left; }
  table.issues-index td:nth-child(5) span.no-pr { color: red; }
  @media (prefers-color-scheme: dark) {
     html {
        color: #ddd;
        background-color: black;
     }
     ins {
        background-color: #225522
     }
     del {
        background-color: #662222
     }
     a {
        color: #6af
     }
     a:visited {
        color: #6af
     }
     blockquote.note
     {
        background-color: rgba(255, 255, 255, .10)
     }
  }
</style>
</head>
<body>
<hr>
<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#TS">TS</a> status.</em></p>
<h3 id="2637"><a href="lwg-defects.html#2637">2637</a>. [filesys.ts] [PDTS] All functions with <code>error_code</code> arguments should be <code>noexcept</code></h3>
<p><b>Section:</b> 15.2 [filesys.ts::fs.op.canonical], 15.11 [filesys.ts::fs.op.current_path], 15.27 [filesys.ts::fs.op.read_symlink], 15.36 [filesys.ts::fs.op.system_complete], 15.37 [filesys.ts::fs.op.temp_dir_path], 99 [filesys.ts::fs.op.unique_path], 8.4 [filesys.ts::path.member] <b>Status:</b> <a href="lwg-active.html#TS">TS</a>
 <b>Submitter:</b> P.J. Plauger <b>Opened:</b> 2014-01-30 <b>Last modified:</b> 2017-07-30</p>
<p><b>Priority: </b>Not Prioritized
</p>
<p><b>View all issues with</b> <a href="lwg-status.html#TS">TS</a> status.</p>
<p><b>Discussion:</b></p>
<p><b>Addresses: filesys.ts</b></p>
<p>
all functions with <code>error_code</code> arguments should be <code>noexcept</code>
(see <code>canonical</code>, <code>current_path</code>, <code>read_symlink</code>, <code>system_complete</code>,
<code>temp_directory_path</code>, <code>unique_path</code>, plus member functions).
</p>
<p><i>[2014-02-03: Stephan T. Lavavej comments:]</i></p>
<p>The declaration and definition of
"<code>recursive_directory_iterator&amp; increment(error_code&amp; ec);</code>" should almost certainly
be marked noexcept.</p>

<p><i>[2014-02-08: Daniel comments]</i></p>

<p>
All functions that return a <code>path</code> value such as <code>canonical</code>, <code>current_path</code>,
<code>read_symlink</code>, <code>system_complete</code>, <code>temp_directory_path</code>, <code>unique_path</code>,
or any member function returning a <code>path</code> value or <code>basic_string</code> value might legally 
throw an exception, if the allocator of the underlying string complains about insufficient 
memory. This is an anti-pattern for <code>noexcept</code>, because the exception-specification includes 
the return statement of a function and given the fact that the language currently does declare RVO
as an optional action, we cannot rely on it.
<p/>
The Standard is currently very careful <em>not</em> to specify functions as <code>noexcept</code>,
if this case can happen, see e.g. <code>std::locale::name()</code>. To the contrary, enforcing them to be
<code>noexcept</code>, would cause a similar problem as the unconditional <code>noexcept</code> specifier of
the value-returning <code>kill_dependency</code> as denoted by LWG <a href="lwg-active.html#2236" title="kill_dependency unconditionally noexcept (Status: SG1)">2236</a><sup><a href="https://cplusplus.github.io/LWG/issue2236" title="Latest snapshot">(i)</a></sup>.
<p/>
Basically this requirement conflicts with the section "Adopted Guidelines", second bullet of
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2011/n3279.pdf">N3279</a>.
</p>

<p><i>[Beman Dawes 2014-02-27]</i></p>


<p/>Issues <a href="lwg-defects.html#2637" title="[filesys.ts] [PDTS] All functions with error_code arguments should be noexcept (Status: TS)">2637</a><sup><a href="https://cplusplus.github.io/LWG/issue2637" title="Latest snapshot">(i)</a></sup>,
<a href="lwg-closed.html#2638" title="[filesys.ts] [PDTS] Make certain functions noexcept and drop error_code version (Status: NAD)">2638</a><sup><a href="https://cplusplus.github.io/LWG/issue2638" title="Latest snapshot">(i)</a></sup>,
<a href="lwg-defects.html#2641" title="[filesys.ts] [PDTS] directory_iterator, recursive_directory_iterator, move construct/assign should be noexcept (Status: TS)">2641</a><sup><a href="https://cplusplus.github.io/LWG/issue2641" title="Latest snapshot">(i)</a></sup>,
and <a href="lwg-defects.html#2649" title="[filesys.ts] [PDTS] path and directory_entry move ctors should not be noexcept (Status: TS)">2649</a><sup><a href="https://cplusplus.github.io/LWG/issue2649" title="Latest snapshot">(i)</a></sup> are concerned with signatures which should or should not
be <code>noexcept</code>. I will provide unified proposed wording for these issues, possibly in a separate paper.

<p><i>[21 May 2014 Beman Dawes reviewed all functions with <code>error_code&amp;</code> arguments,
  and provided proposed wording for the one case found where the above guidelines were not met.
  This was the case previously identified by Stephan T. Lavavej.
]</i></p>




<p id="res-2637"><b>Proposed resolution:</b></p>
  <p>
    <i>Change 14 Class recursive_directory_iterator [class.rec.dir.itr]:</i>
  </p>
  <blockquote>
    <pre>recursive_directory_iterator&amp; increment(error_code&amp; ec) <ins>noexcept</ins>;</pre>
  </blockquote>
  <p>
    <i>Change 14.1 recursive_directory_iterator members [rec.dir.itr.members]:</i>
  </p>
  <blockquote>
    <pre>recursive_directory_iterator&amp; increment(error_code&amp; ec) <ins>noexcept</ins>;</pre>
  </blockquote>





</body>
</html>
