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<title>Issue 2497: Use of uncaught_exception()</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="2497"><a href="lwg-active.html#2497">2497</a>. Use of <code>uncaught_exception()</code></h3>
<p><b>Section:</b> 31.7.6.2.4 <a href="https://wg21.link/ostream.sentry">[ostream.sentry]</a> <b>Status:</b> <a href="lwg-active.html#New">New</a>
 <b>Submitter:</b> Roger Orr <b>Opened:</b> 2015-05-08 <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#ostream.sentry">issues</a> in [ostream.sentry].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#New">New</a> status.</p>
<p><b>Discussion:</b></p>
<p>
In the current 31.7.6.2.4 <a href="https://wg21.link/ostream.sentry">[ostream.sentry]</a>, p4 refers to the now deprecated <code>std::uncaught_exception()</code>: 
D.9 [depr.uncaught].
</p>
<blockquote>
<p>
If <code>((os.flags() &amp; ios_base::unitbuf) &amp;&amp; !uncaught_exception() &amp;&amp; os.good())</code> is true, calls
<code>os.rdbuf()->pubsync()</code>.
</p>
</blockquote>
<p>
This needs to be changed, for example to use <code>std::uncaught_exceptions()</code> and to capture the value on entry and 
compare with the saved value on exit.
</p>

<p><i>[2015-06, Telecon]</i></p>

<p>
JW: I already added an 's' here to make it use the new function, but that doesn't resolve Roger's suggestion to capture the value on entry and check it.
</p>

<p><i>[2019-03-21; Daniel comments and provides wording]</i></p>

<p>
The wording below implements Roger's suggestion.
</p>


<p id="res-2497"><b>Proposed resolution:</b></p>
<p>This wording is relative to <a href="https://wg21.link/n4810">N4810</a>.</p>

<ol>
<li><p>Modify 31.7.6.2.4 <a href="https://wg21.link/ostream.sentry">[ostream.sentry]</a>, class <code>basic_ostream::sentry</code> synopsis, as indicated:</p>

<blockquote>
<pre>
namespace std {
  template&lt;class charT, class traits = char_traits&lt;charT&gt;&gt;
  class basic_ostream&lt;charT, traits&gt;::sentry {
    bool ok_; <i>// exposition only</i>
    <ins>int uncaught_ = uncaught_exceptions(); <i>// exposition only</i></ins>
  public:
    explicit sentry(basic_ostream&lt;charT, traits&gt;&amp; os);
    ~sentry();
    explicit operator bool() const { return ok_; }
    sentry(const sentry&amp;) = delete;
    sentry&amp; operator=(const sentry&amp;) = delete;
  };
}
</pre>
<p>
[&hellip;]
</p>
<pre>
~sentry();
</pre>
<blockquote>
<p>
-4- If <code>(os.flags() &amp; ios_base::unitbuf) &amp;&amp; <del>!</del>uncaught_exceptions() <ins>&lt;= uncaught_</ins> 
&amp;&amp; os.good()</code> is <code>true</code>, calls <code>os.rdbuf()-&gt;pubsync()</code>. If that function returns <code>-1</code>, 
sets <code>badbit</code> in <code>os.rdstate()</code> without propagating an exception.
</p>
</blockquote>
</blockquote>
</li>
</ol>





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