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<title>Issue 3667: std::cout &lt;&lt; &amp;X::f prints 1</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#NAD">NAD</a> status.</em></p>
<h3 id="3667"><a href="lwg-closed.html#3667">3667</a>. <code>std::cout &lt;&lt; &amp;X::f</code> prints <code>1</code></h3>
<p><b>Section:</b> 31.7.6.3 <a href="https://wg21.link/ostream.formatted">[ostream.formatted]</a> <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a>
 <b>Submitter:</b> Peter Dimov <b>Opened:</b> 2022-01-31 <b>Last modified:</b> 2022-08-23</p>
<p><b>Priority: </b>Not Prioritized
</p>
<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p>
<p><b>Discussion:</b></p>
<p>
At present, the program
</p>
<blockquote><pre>
#include &lt;iostream&gt;

struct X
{
  void f() {}
};

int main()
{
  std::cout &lt;&lt; &amp;X::f;
}
</pre></blockquote>
<p>
prints <code>1</code>. That's because member pointers implicitly convert
to <code>bool</code>, and there's <code>operator&lt;&lt;</code> overload for <code>bool</code> in
31.7.6.3.2 <a href="https://wg21.link/ostream.inserters.arithmetic">[ostream.inserters.arithmetic]</a>.
<p/>
This behavior is rarely useful. In C++20, we added deleted
overloads to prevent a similar counter-intuitive output for
the case in which e.g. <code>L"str"</code> is output to <code>std::cout</code>,
which used to print the pointer value using the <code>operator&lt;&lt;</code>
overload for <code>const void*</code>.
<p/>
We should similarly consider adding a deleted overload for member pointers.
</p>

<p><i>[2022-03-04; Reflector poll; Status changed: New &rarr; Tentatively NAD]</i></p>

<p>
 Needs a paper to LEWG if anything should change here.
</p>
<p><i>[2022-08-23 Status changed: Tentatively NAD &rarr; NAD.]</i></p>



<p id="res-3667"><b>Proposed resolution:</b></p>
<p>
This wording is relative to <a href="https://wg21.link/N4901" title=" Working Draft, Standard for Programming Language C++">N4901</a>.
</p>

<ol>
<li><p>Modify 31.7.6.2.1 <a href="https://wg21.link/ostream.general">[ostream.general]</a>, class template <code>basic_ostream</code> synopsis, as indicated:</p>

<blockquote>
<pre>
namespace std {
  [&hellip;]
  
  template&lt;class traits&gt;
    basic_ostream&lt;wchar_t, traits&gt;&amp;
      operator&lt;&lt;(basic_ostream&lt;wchar_t, traits&gt;&amp;, const char16_t*) = delete;
  template&lt;class traits&gt;
    basic_ostream&lt;wchar_t, traits&gt;&amp;
      operator&lt;&lt;(basic_ostream&lt;wchar_t, traits&gt;&amp;, const char32_t*) = delete;
      
  <ins>template&lt;class charT, class traits, class T, class C&gt;
    basic_ostream&lt;charT, traits&gt;&amp; 
      operator&lt;&lt;(basic_ostream&lt;charT, traits&gt;&amp;, T C::*) = delete;</ins>
}
</pre>
</blockquote>
</li>
</ol>





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