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<title>Issue 3056: copy_file() copies which attributes?</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="3056"><a href="lwg-active.html#3056">3056</a>. <code>copy_file()</code> copies which attributes?</h3>
<p><b>Section:</b> 31.12.13.5 <a href="https://wg21.link/fs.op.copy.file">[fs.op.copy.file]</a> <b>Status:</b> <a href="lwg-active.html#New">New</a>
 <b>Submitter:</b> Davis Herring <b>Opened:</b> 2018-01-26 <b>Last modified:</b> 2020-09-06</p>
<p><b>Priority: </b>3
</p>
<p><b>View all other</b> <a href="lwg-index.html#fs.op.copy.file">issues</a> in [fs.op.copy.file].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#New">New</a> status.</p>
<p><b>Discussion:</b></p>
<p>
(To resolve <a href="https://wg21.link/p0489r0#page=5">C++17 CD comment Late 25</a>.) 
It is not stated which attributes are copied by <code>copy_file()</code>.
</p>

<p><i>[2018-1-26 issues processing telecon]</i></p>

<p>Priority 3</p>


<p id="res-3056"><b>Proposed resolution:</b></p>
<p>This wording is relative to <a href="https://wg21.link/n4713">N4713</a>.</p>
<ol>
<li><p>Modify 31.12.13.5 <a href="https://wg21.link/fs.op.copy.file">[fs.op.copy.file]</a> as indicated:</p>

<blockquote class="note">
<p>
<b>Rationale:</b>
<p/>
The attributes specified are the useful subset of the attributes that can be queried in C++17.  
Existing practice is complicated: POSIX "cp -p" attempts to preserve user/group IDs, for instance, 
but cannot in general do so, and <code>setuid/setgid</code> permissions may be stripped.
</p>
</blockquote>

<blockquote>
<pre>
bool copy_file(const path&amp; from, const path&amp; to, copy_options options);
bool copy_file(const path&amp; from, const path&amp; to, copy_options options,
               error_code&amp; ec) noexcept;
</pre>
<blockquote>
<p>
[&hellip;]
<ol style="list-style-type: none">
<li><p>[&hellip;]</p></li>
<li><p>(4.2) &mdash; Otherwise, copy the contents<ins>, permissions, and data modification time</ins> 
<del>and attributes</del> of the file <code>from</code> resolves to, to the file <code>to</code> resolves to, if:</p></li>
<li><p>[&hellip;]</p></li>
<li>
<ol style="list-style-type: none">
<li><p>(4.2.3) &mdash; <code>(options &amp; copy_options::update_existing) != copy_options::none</code> 
and <code>from</code> is more recent than <code>to</code>, determined as if by use of the <code>last_write_time</code> 
function (31.12.13.26 <a href="https://wg21.link/fs.op.last.write.time">[fs.op.last.write.time]</a>).</p></li>
</ol>
<p>
<ins>Other implementation-defined attributes may be copied. Failure (or partial failure) to copy attributes 
is not an error.</ins>
</p>
</li>
<li><p>[&hellip;]</p></li>
</ol>
[&hellip;]
</p>
</blockquote>
</blockquote>
</li>
</ol>





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