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<title>Issue 2672: Should is_empty use error_code in its specification?</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="2672"><a href="lwg-defects.html#2672">2672</a>. Should is_empty use error_code in its specification?</h3>
<p><b>Section:</b> 31.12.13.20 <a href="https://wg21.link/fs.op.is.empty">[fs.op.is.empty]</a> <b>Status:</b> <a href="lwg-active.html#C++17">C++17</a>
 <b>Submitter:</b> Jonathan Wakely <b>Opened:</b> 2014-08-01 <b>Last modified:</b> 2021-06-06</p>
<p><b>Priority: </b>3
</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 descriptions of most functions are explicit about the use of the <code>ec</code> argument,
  either saying something like "<code>foo(p)</code> or <code>foo(p, ec)</code>, respectively" or using the
  <code>ec</code> argument like <code>foo(p[, ec])</code>, but <code>is_empty</code> does not.
</p>
<p>
 [fs.op.is_empty]/2 refers to <code>ec</code> unconditionally, but more importantly
   [fs.op.is_empty]/3 doesn't pass <code>ec</code> to the <code>directory_iterator</code>
  constructor or the <code>file_size</code> function.
</p>

  <p><i>[
    9 Oct 2014 Beman supplies proposed wording.
  ]</i></p>


<p><i>[<b>Apr 2016 Issue updated to address the C++ Working Paper. Previously addressed File System TS</b>]</i></p>


<p><strong>Previous resolution [SUPERSEDED]:</strong></p>
<blockquote class="note">
<ol>
<li>
  <blockquote>
  <pre>
    bool is_empty(const path&amp; p);
    bool is_empty(const path&amp; p, error_code&amp; ec) noexcept;
  </pre>
  <blockquote>
    <p>
      <i>Effects:</i>
    </p>
    <ul>
      <li>
        Determine <code>file_status s</code>, as if by
        <ins>
          <code>status(p)</code> or
        </ins> <code>status(p, ec)</code><ins>, respectively</ins>.
      </li>
      <li>
        <ins>
          For the signature with argument <code>ec</code>, return <code>false</code> if
          an error occurred.
        </ins>
      </li>
      <li>
        <ins>
          Otherwise, if <code>is_directory(s)</code>:
        </ins>
        <ul>
          <li>
            <ins>
              Create <code>directory_iterator itr</code>, as if by
              <code>directory_iterator(p)</code>
              or <code>directory_iterator(p, ec)</code>, respectively.
            </ins>
          </li>
          <li>
            <ins>
              For the signature with argument <code>ec</code>, return <code>false</code> if
              an error occurred.
            </ins>
          </li>
          <li>
            <ins>
              Otherwise, return <code>itr == directory_iterator()</code>.
            </ins>
          </li>
        </ul>
      </li>
      <li>
        <ins>Otherwise:</ins>
        <ul>
          <li>
            <ins>
              Determine <code>uintmax_t sz</code>, as if by <code>
                file_size(p)
              </code> or<code> file_size(p, ec)</code>, respectively
            </ins>.
          </li>
          <li>
            <ins>
              For the signature with argument <code>ec</code>, return <code>false</code> if
              an error occurred.
            </ins>
          </li>
          <li>
            <ins>
              Otherwise, return <code>sz == 0</code>.
            </ins>
          </li>
        </ul>
      </li>
    </ul>
    <p>
      <ins>
        <i>Remarks:</i> The temporary objects described in <i>Effects</i>
        are for exposition only. Implementations are not required to create them.
      </ins>
    </p>
    <p>
      <i>Returns:</i>
      <del>
        <code>
          is_directory(s) ? directory_iterator(p) == directory_iterator()
          : file_size(p) == 0;
        </code>
      </del>
      <ins>
        See <i>Effects</i>.
      </ins>
    </p>
    <blockquote>
      <p>
        <del>
          The signature with argument <code>ec</code> returns <code>false</code> if
          an error occurs.
        </del>
      </p>
    </blockquote>
    <p>
      <i>Throws:</i> As specified in Error reporting (7).
    </p>
  </blockquote>
  </blockquote>
</li>
</ol>
</blockquote>

<p><i>[2016-08 Chicago]</i></p>

<p>Wed PM: Move to Tentatively Ready</p>


<p id="res-2672"><b>Proposed resolution:</b></p>
<ol>
<li>
  <blockquote>
  <pre>
    bool is_empty(const path&amp; p);
    bool is_empty(const path&amp; p, error_code&amp; ec) noexcept;
  </pre>
  <blockquote>
    <p>
      <i>Effects:</i>
    </p>
    <ul>
      <li>
        Determine <code>file_status s</code>, as if by
        <ins>
          <code>status(p)</code> or
        </ins> <code>status(p, ec)</code><ins>, respectively</ins>.
      </li>
      <li>
        <ins>
          For the signature with argument <code>ec</code>, return <code>false</code> if
          an error occurred.
        </ins>
      </li>
      <li>
        <ins>
          Otherwise, if <code>is_directory(s)</code>:
        </ins>
        <ul>
          <li>
            <ins>
              Create <code>directory_iterator itr</code>, as if by
              <code>directory_iterator(p)</code>
              or <code>directory_iterator(p, ec)</code>, respectively.
            </ins>
          </li>
          <li>
            <ins>
              For the signature with argument <code>ec</code>, return <code>false</code> if
              an error occurred.
            </ins>
          </li>
          <li>
            <ins>
              Otherwise, return <code>itr == directory_iterator()</code>.
            </ins>
          </li>
        </ul>
      </li>
      <li>
        <ins>Otherwise:</ins>
        <ul>
          <li>
            <ins>
              Determine <code>uintmax_t sz</code>, as if by <code>
                file_size(p)
              </code> or<code> file_size(p, ec)</code>, respectively
            </ins>.
          </li>
          <li>
            <ins>
              For the signature with argument <code>ec</code>, return <code>false</code> if
              an error occurred.
            </ins>
          </li>
          <li>
            <ins>
              Otherwise, return <code>sz == 0</code>.
            </ins>
          </li>
        </ul>
      </li>
    </ul>
    <p>
      <del>
      <i>Returns:</i>
        <code>
          is_directory(s) ? directory_iterator(p) == directory_iterator()
          : file_size(p) == 0;
        </code>
      </del>
    </p>
    <blockquote>
      <p>
        <del>
          The signature with argument <code>ec</code> returns <code>false</code> if
          an error occurs.
        </del>
      </p>
    </blockquote>
    <p>
      <i>Throws:</i> As specified in Error reporting (7).
    </p>
  </blockquote>
  </blockquote>
</li>
</ol>





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