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<title>Issue 116: bitset cannot be constructed with a const char*</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#Dup">Dup</a> status.</em></p>
<h3 id="116"><a href="lwg-closed.html#116">116</a>. bitset cannot be constructed with a const char*</h3>
<p><b>Section:</b> 22.9.2 <a href="https://wg21.link/template.bitset">[template.bitset]</a> <b>Status:</b> <a href="lwg-active.html#Dup">Dup</a>
 <b>Submitter:</b> Judy Ward <b>Opened:</b> 1998-11-06 <b>Last modified:</b> 2016-01-28</p>
<p><b>Priority: </b>Not Prioritized
</p>
<p><b>View other</b> <a href="lwg-index-open.html#template.bitset">active issues</a> in [template.bitset].</p>
<p><b>View all other</b> <a href="lwg-index.html#template.bitset">issues</a> in [template.bitset].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#Dup">Dup</a> status.</p>
<p><b>Duplicate of:</b> <a href="lwg-defects.html#778" title="std::bitset does not have any constructor taking a string literal (Status: CD1)">778</a></p>
<p><b>Discussion:</b></p>



<p>The following code does not compile with the EDG compiler:</p>

<blockquote>
  <pre>#include &lt;bitset&gt;
using namespace std;
bitset&lt;32&gt; b(&quot;111111111&quot;);</pre>
</blockquote>

<p>If you cast the ctor argument to a string, i.e.:</p>

<blockquote>
  <pre>bitset&lt;32&gt; b(string(&quot;111111111&quot;));</pre>
</blockquote>

<p>then it will compile. The reason is that bitset has the following templatized
constructor:</p>

<blockquote>
  <pre>template &lt;class charT, class traits, class Allocator&gt;
explicit bitset (const basic_string&lt;charT, traits, Allocator&gt;&amp; str, ...);</pre>
</blockquote>

<p>According to the compiler vendor, Steve Adamcyk at EDG, the user
cannot pass this template constructor a <code>const char*</code> and
expect a conversion to <code>basic_string</code>.  The reason is
&quot;When you have a template constructor, it can get used in
contexts where type deduction can be done. Type deduction basically
comes up with exact matches, not ones involving conversions.&quot;
</p>

<p>I don't think the intention when this constructor became
templatized was for construction from a <code>const char*</code> to no
longer work.</p>


<p id="res-116"><b>Proposed resolution:</b></p>
<p>Add to 22.9.2 <a href="https://wg21.link/template.bitset">[template.bitset]</a> a bitset constructor declaration</p>

<blockquote>
  <pre>explicit bitset(const char*);</pre>
</blockquote>

<p>and in Section 22.9.2.2 <a href="https://wg21.link/bitset.cons">[bitset.cons]</a> add:</p>

<blockquote>
  <pre>explicit bitset(const char* str);</pre>
  <p>Effects: <br/>
  &nbsp;&nbsp;&nbsp; Calls <code>bitset((string) str, 0, string::npos);</code></p>
</blockquote>


<p><b>Rationale:</b></p>
<p>Although the problem is real, the standard is designed that way so
it is not a defect.  Education is the immediate workaround. A future
standard may wish to consider the Proposed Resolution as an
extension.</p>





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