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POComparing STL strings that use different allocators
 

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    <p>I'd like to compare STL strings that are allocated with <strong>different allocators</strong>, e.g. an ordinary <code>std::string</code> with a string using a <em>custom STL allocator</em>. Unfortunately, it seems that usual <code>operator==()</code> doesn't work in this case:</p> <pre><code>// Custom STL allocator to allocate char's for string class typedef MyAllocator&lt;char&gt; MyCharAllocator; // Define an instance of this allocator MyCharAllocator myAlloc; // An STL string with custom allocator typedef std::basic_string &lt; char, std::char_traits&lt;char&gt;, MyCharAllocator &gt; CustomAllocString; std::string s1("Hello"); CustomAllocString s2("Hello", myAlloc); if (s1 == s2) // &lt;--- ERROR: doesn't compile ... </code></pre> <p>In particular, MSVC10 (VS2010 SP1) emits the following error message:</p> <blockquote> <p>error C2678: binary '==' : no operator found which takes a left-hand operand of type 'std::string' (or there is no acceptable conversion)</p> </blockquote> <p>So, a <em>lower-level</em> (less readable) code like this:</p> <pre><code>if (strcmp(s1.c_str(), s2.c_str()) == 0) ... </code></pre> <p>should be used.</p> <p>(This is also particularly annoying in cases where e.g. there are <code>std::vector</code>'s of differently-allocated strings, where the usual simple <code>v[i] == w[j]</code> syntax can't be used.)</p> <p>This doesn't seem very good to me, since a custom allocator changes the way string memory is requested, but the <em>interface</em> of a string class (including comparison with <code>operator==()</code>) is independent from the particular way a string allocates its memory.</p> <p>Is there something I am missing here? Is it possible to keep the C++ high-level interface and operator overloads in this case?</p>
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    1. COHey, look. A good question.
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      1. USJohn Dibling
    2. CO@JohnDibling: Thanks.
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