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<title>Issue 117: basic_ostream uses nonexistent num_put member functions</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#CD1">CD1</a> status.</em></p>
<h3 id="117"><a href="lwg-defects.html#117">117</a>. <code>basic_ostream</code> uses nonexistent <code>num_put</code> member functions</h3>
<p><b>Section:</b> 31.7.6.3.2 <a href="https://wg21.link/ostream.inserters.arithmetic">[ostream.inserters.arithmetic]</a> <b>Status:</b> <a href="lwg-active.html#CD1">CD1</a>
 <b>Submitter:</b> Matt Austern <b>Opened:</b> 1998-11-20 <b>Last modified:</b> 2016-01-28</p>
<p><b>Priority: </b>Not Prioritized
</p>
<p><b>View all other</b> <a href="lwg-index.html#ostream.inserters.arithmetic">issues</a> in [ostream.inserters.arithmetic].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#CD1">CD1</a> status.</p>
<p><b>Discussion:</b></p>
<p>The <b>effects</b> clause for numeric inserters says that
insertion of a value <code>x</code>, whose type is either <code>bool</code>,
<code>short</code>, <code>unsigned short</code>, <code>int</code>, <code>unsigned
int</code>, <code>long</code>, <code>unsigned long</code>, <code>float</code>,
<code>double</code>, <code>long double</code>, or <code>const void*</code>, is
delegated to <code>num_put</code>, and that insertion is performed as if
through the following code fragment: </p>

<pre>bool failed = use_facet&lt;
   num_put&lt;charT,ostreambuf_iterator&lt;charT,traits&gt; &gt; 
   &gt;(getloc()).put(*this, *this, fill(), val). failed();</pre>

<p>This doesn't work, because <code>num_put&lt;&gt;</code>::put is only
overloaded for the types <code>bool</code>, <code>long</code>, <code>unsigned
long</code>, <code>double</code>, <code>long double</code>, and <code>const
void*</code>. That is, the code fragment in the standard is incorrect
(it is diagnosed as ambiguous at compile time) for the types
<code>short</code>, <code>unsigned short</code>, <code>int</code>, <code>unsigned
int</code>, and <code>float</code>. </p>

<p>We must either add new member functions to <code>num_put</code>, or
else change the description in <code>ostream</code> so that it only calls
functions that are actually there. I prefer the latter. </p>


<p id="res-117"><b>Proposed resolution:</b></p>
<p>Replace 27.6.2.5.2, paragraph 1 with the following: </p>

<blockquote>
<p>
The classes num_get&lt;&gt; and num_put&lt;&gt; handle locale-dependent numeric
formatting and parsing.  These inserter functions use the imbued
locale value to perform numeric formatting.  When val is of type bool,
long, unsigned long, double, long double, or const void*, the
formatting conversion occurs as if it performed the following code
fragment:
</p>

<pre>
bool failed = use_facet&lt;
   num_put&lt;charT,ostreambuf_iterator&lt;charT,traits&gt; &gt;
   &gt;(getloc()).put(*this, *this, fill(), val). failed();
</pre>

<p>
When val is of type short the formatting conversion occurs as if it
performed the following code fragment:
</p>

<pre>
ios_base::fmtflags baseflags = ios_base::flags() &amp; ios_base::basefield;
bool failed = use_facet&lt;
   num_put&lt;charT,ostreambuf_iterator&lt;charT,traits&gt; &gt;
   &gt;(getloc()).put(*this, *this, fill(),
      baseflags == ios_base::oct || baseflags == ios_base::hex
         ? static_cast&lt;long&gt;(static_cast&lt;unsigned short&gt;(val))
         : static_cast&lt;long&gt;(val)). failed();
</pre>

<p>
When val is of type int the formatting conversion occurs as if it performed
the following code fragment:
</p>

<pre>
ios_base::fmtflags baseflags = ios_base::flags() &amp; ios_base::basefield;
bool failed = use_facet&lt;
   num_put&lt;charT,ostreambuf_iterator&lt;charT,traits&gt; &gt;
   &gt;(getloc()).put(*this, *this, fill(),
      baseflags == ios_base::oct || baseflags == ios_base::hex
         ? static_cast&lt;long&gt;(static_cast&lt;unsigned int&gt;(val))
         : static_cast&lt;long&gt;(val)). failed();
</pre>

<p>
When val is of type unsigned short or unsigned int the formatting conversion
occurs as if it performed the following code fragment:
</p>

<pre>
bool failed = use_facet&lt;
   num_put&lt;charT,ostreambuf_iterator&lt;charT,traits&gt; &gt;
   &gt;(getloc()).put(*this, *this, fill(), static_cast&lt;unsigned long&gt;(val)).
failed();
</pre>

<p>
When val is of type float the formatting conversion occurs as if it
performed the following code fragment:
</p>

<pre>
bool failed = use_facet&lt;
   num_put&lt;charT,ostreambuf_iterator&lt;charT,traits&gt; &gt;
   &gt;(getloc()).put(*this, *this, fill(), static_cast&lt;double&gt;(val)).
failed();
</pre>

</blockquote>

<p><i>[post-Toronto: This differs from the previous proposed
resolution; PJP provided the new wording.  The differences are in
signed short and int output.]</i></p>



<p><b>Rationale:</b></p>
<p>The original proposed resolution was to cast int and short to long,
unsigned int and unsigned short to unsigned long, and float to double,
thus ensuring that we don't try to use nonexistent num_put&lt;&gt;
member functions.  The current proposed resolution is more
complicated, but gives more expected results for hex and octal output
of signed short and signed int.  (On a system with 16-bit short, for
example, printing short(-1) in hex format should yield 0xffff.)</p>





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