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<title>Issue 2233: bad_function_call::what() unhelpful</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="2233"><a href="lwg-defects.html#2233">2233</a>. <code>bad_function_call::what()</code> unhelpful</h3>
<p><b>Section:</b> 22.10.17.2 <a href="https://wg21.link/func.wrap.badcall">[func.wrap.badcall]</a> <b>Status:</b> <a href="lwg-active.html#C++17">C++17</a>
 <b>Submitter:</b> Jonathan Wakely <b>Opened:</b> 2013-01-05 <b>Last modified:</b> 2017-09-07</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>
A strict reading of the standard implies <code>std::bad_function_call{}.what()</code> returns the same string as
<code>std::exception{}.what()</code> which doesn't help to know what happened if you catch an exception by reference 
to <code>std::exception</code>.
</p>

<p>
For consistency with <code>bad_weak_ptr::what()</code> it should return <code>"bad_function_call"</code>.
</p>

<p>
See <a href="http://listarchives.isocpp.org/cgi-bin/wg21/message?wg=lib&amp;msg=33515">c++std-lib-33515</a> for other details.
</p>

<p>
There was a considerable support on the reflector to instead change the specification of both <code>bad_weak_ptr::what()</code> 
and <code>bad_function_call::what()</code> to return an implementation-defined string instead.
</p>

<p><i>[2013-03-15 Issues Teleconference]</i></p>

<p>
Moved to Open.
</p>
<p>
Consensus that we want consistency in how this is treated.  Less consensus on what the common
direction should be.
</p>
<p>
Alisdair to provide wording proposing that all string literals held by standard exception objects are
either unspecified, or implmentation defined.
</p>

<p><i>[2014-02-15 Issauqah]</i></p>

<p>
STL: I think it should be an implementation-defined NTBS, same on <code>bad_weak_ptr</code>. I will write a PR.
</p>

<p><i>[2014-03-27, STL provides improved wording]</i></p>


<p>
The new wording reflects better the general agreement of the committee, see also issue <a href="lwg-defects.html#2376" title="bad_weak_ptr::what() overspecified (Status: C++17)">2376</a><sup><a href="https://cplusplus.github.io/LWG/issue2376" title="Latest snapshot">(i)</a></sup> for similar wording.
</p>

<p><i>[2014-03-28 Library reflector vote]</i></p>

<p>
The issue has been identified as Tentatively Ready based on five votes in favour.
</p>



<p id="res-2233"><b>Proposed resolution:</b></p>
<p>This wording is relative to N3936.</p>

<ol>
<li><p>Edit  [func.wrap.badcall.const]:</p>
<blockquote><pre>
bad_function_call() noexcept;
</pre><blockquote>
<p>
-1- <i>Effects</i>: constructs a <code>bad_function_call object</code>.
<p/>
<ins>-?- <i>Postconditions</i>: <code>what()</code> returns an implementation-defined NTBS.</ins>
</p>
</blockquote></blockquote>
</li>
</ol>






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