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<title>Issue 2725: filesystem::exists(const path&amp;, error_code&amp;) error reporting</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++17">C++17</a> status.</em></p>
<h3 id="2725"><a href="lwg-defects.html#2725">2725</a>. <code>filesystem::exists(const path&amp;, error_code&amp;)</code> error reporting</h3>
<p><b>Section:</b> 31.12.13.14 <a href="https://wg21.link/fs.op.exists">[fs.op.exists]</a> <b>Status:</b> <a href="lwg-active.html#C++17">C++17</a>
 <b>Submitter:</b> Jonathan Wakely <b>Opened:</b> 2016-06-06 <b>Last modified:</b> 2017-07-30</p>
<p><b>Priority: </b>1
</p>
<p><b>View all issues with</b> <a href="lwg-status.html#C++17">C++17</a> status.</p>
<p><b>Discussion:</b></p>
<p>
The <code>filesystem::exists(const path&amp;)</code> function does not throw an
exception if the file doesn't exist, but the corresponding function
taking an <code>error_code&amp;</code> argument does set it to indicate an error.
<p/>
It seems sensible for <code>filesystem::exists(const path&amp;, error_code&amp;)</code> to
call <code>ec.clear()</code> if <code>status(p, ec).type() == file_type::not_found</code>.
</p>

<p><i>[2016-06, Oulu &mdash; Jonathan comments and provides wording]</i></p>

<p>
The sentence "The signature with argument <code>ec</code> returns <code>false</code> if an error
occurs." means that given a file such that <code>status(p).type() == file_type::unknown</code>, 
<code>exists(p)</code> is <code>true</code> but <code>exists(p, ec)</code> is <code>false</code>.
<p/>
I believe we should make the behaviour of <code>exists(p)</code> and <code>exists(p, ec)</code>
consistent, so that the latter clears <code>ec</code> except when the former would
throw an exception, which is only for the <code>file_type::none</code> case.
</p>
<p><i>[2016-06, Oulu]</i></p>

<p>Prioritized as P1</p>
<p>Voted to Ready 7-0 Tuesday evening in Oulu</p>


<p id="res-2725"><b>Proposed resolution:</b></p>
<p>This wording is relative to N4594.</p>
<ol>
<li><p>Insert a new paragraph before 31.12.13.14 <a href="https://wg21.link/fs.op.exists">[fs.op.exists]</a> p2 and edit it as shown:</p>

<blockquote>
<pre>
bool exists(const path&amp; p);
bool exists(const path&amp; p, error_code&amp; ec) noexcept;
</pre>
<blockquote>
<p>
<ins>-?- Let <code>s</code> be a <code>file_status</code>, determined as if by <code>status(p)</code> or <code>status(p, ec)</code>, 
respectively.</ins>
<p/>
<ins>-?- <i>Effects:</i> The signature with argument <code>ec</code> calls <code>ec.clear()</code> if <code>status_known(s)</code>.</ins>
<p/>
-2- <i>Returns:</i> <del><code>exists(status(p))</code> or <code>exists(status(p, ec))</code>, respectively</del><ins><code>exists(s)</code></ins>. 
<del>The signature with argument <code>ec</code> returns <code>false</code> if an error occurs</del>.
</p>
</blockquote>
</blockquote>
</li>
</ol>





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