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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++11">C++11</a> status.</em></p>
<h3 id="1325"><a href="lwg-defects.html#1325">1325</a>. <code>bitset</code></h3>
<p><b>Section:</b> 22.9.2.2 <a href="https://wg21.link/bitset.cons">[bitset.cons]</a> <b>Status:</b> <a href="lwg-active.html#C++11">C++11</a>
 <b>Submitter:</b> Christopher Jefferson <b>Opened:</b> 2010-03-07 <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#bitset.cons">issues</a> in [bitset.cons].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#C++11">C++11</a> status.</p>
<p><b>Discussion:</b></p>
<p>
As mentioned on the boost mailing list:
</p>

<p>
The following code, valid in C++03, is broken in C++0x due to ambiguity
between the "<code>unsigned long long</code>" and "<code>char*</code>"
constructors.
</p>

<blockquote><pre>
#include &lt;bitset&gt;
std::bitset&lt;10&gt; b(0);
</pre></blockquote>

<p><i>[
The proposed resolution has been reviewed by Stephan T. Lavavej.
]</i></p>


<p><i>[
Post-Rapperswil
]</i></p>


<p>
The proposed resolution has two problems:
</p>
<ul>
<li>
<p>it fails to provide support for non-terminated strings, which
could be easily added and constitutes an important use-case. For
example, the following code would invoke UB with the current
P/R:</p>
<blockquote>
<pre>
char s[4] = { '0', '1', '0', '1' }; // notice: not null-terminated!
bitset&lt;4&gt; b(s, 0, 4);
</pre></blockquote>
because it requires the evaluation (under the as-if rule, to be fair,
but it doesn't matter) of <code>basic_string&lt;char&gt;(s)</code>
</li>
<li>
<p>it promotes a consistency between the two <code>bitset</code>
constructors that take a <code>const std::string&amp;</code> and a
<code>const char*</code>, respectively, while practice established by
<code>std::basic_string</code> would recommend a different set of
parameters. In particular, the constructor of
<code>std::basic_string</code> that takes a <code>const char*</code> does
not have a <code>pos</code> parameter</p>
</li>
</ul>

<blockquote><p>
Moved to Tentatively Ready with revised wording provided by Alberto 
Ganesh Babati after 5 positive votes on c++std-lib.
</p></blockquote>

<p><i>[
Adopted at 2010-11 Batavia
]</i></p>




<p id="res-1325"><b>Proposed resolution:</b></p>


<ol>
<li>In the synopsis of header <code>&lt;bitset&gt;</code> in
22.9.2 <a href="https://wg21.link/template.bitset">[template.bitset]</a>/1, replace the fourth bitset constructor:
<blockquote>
<pre>
<del>explicit bitset(const char *str);</del>
<ins>template &lt;class charT&gt;
  explicit bitset(
    const charT *str,
    typename basic_string&lt;charT&gt;::size_type n = basic_string&lt;charT&gt;::npos,
    charT zero = charT('0'), charT one = charT('1'));</ins>
</pre></blockquote>
</li>
<li>In 22.9.2.2 <a href="https://wg21.link/bitset.cons">[bitset.cons]</a>/8:
<blockquote>
<pre>
<del>explicit bitset(const char *str);</del>
<ins>template &lt;class charT&gt;
explicit
bitset(const charT *str,
       typename basic_string&lt;charT&gt;::size_type n = basic_string&lt;charT&gt;::npos,
       charT zero = charT('0'), charT one = charT('1'));</ins>
</pre></blockquote>
<p>
Effects: Constructs an object of class
<code>bitset&lt;N&gt;</code> as if by
<del>bitset(string(str)).</del>
</p>
<blockquote><pre><ins>
bitset(
  n == basic_string&lt;charT&gt;::npos
    ? basic_string&lt;charT&gt;(str)
    : basic_string&lt;charT&gt;(str, n),
  0, n, zero, one)
</ins></pre></blockquote>
</li>
</ol>






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