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POHow to get rid of C4800 warning produced by boost::flyweight in VS2008
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  1. POHow to get rid of C4800 warning produced by boost::flyweight in VS2008
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    copied!<p>I get a warning when compiling below code in VS2008 with MFC turned on. Boost version 1.39</p> <pre><code> include "boost/flyweight.hpp" include "boost/flyweight/key_value.hpp" class Foo { public: Foo(const CString& item) : mfoo(item) {} const CString& getkeyvalue() const {return mfoo;} private: const CString mfoo; }; struct Conversion { const CString& operator() (const Foo& item) const {return item.getkeyvalue();} }; using namespace boost::flyweights; flyweight&lt;key_value&lt;CString, Foo, Conversion&gt;, tag&lt;Foo&gt; &gt; flyweight_test; </code></pre> <p>The last line in the above code produces a warning</p> <p>d:\work\sourcecode\boost1390\boost\functional\hash\extensions.hpp(72) : warning C4800: <code>'const wchar_t *'</code> : forcing value to bool 'true' or 'false' (performance warning)<br> d:\work\sourcecode\boost1390\boost\functional\hash\extensions.hpp(71) : while compiling class template member function <code>size_t boost::hash&lt;T&gt;::operator ()(const T &amp;) const</code> with<br> [<br> <code>T=ATL::CStringT&lt;wchar_t,StrTraitMFC_DLL&lt;wchar_t&gt;&gt;</code><br> ]<br> d:\work\sourcecode\boost1390\boost\multi_index\hashedindex.hpp(1159) : see reference to class template instantiation 'boost::hash&lt;T&gt;' being compiled with<br> [<br> <code>T=ATL::CStringT&lt;wchar_t,StrTraitMFC_DLL&lt;wchar_t&gt;&gt;</code><br> ] </p> <p>This warning goes on and on, through hashed factory, MPL, etc.</p> <p>Why is the warning there and how do I correct the code so no warning is produced? </p> <p>Edit:<br> To fix, add below implementation of hash_value </p> <pre><code> template&lt;typename CharType, typename TraitsType&gt; std::size_t hash_value(const ATL::CStringT&lt;CharType, TraitsType&gt;& s) { return CStringElementTraits&lt;typename TraitsType&gt;::Hash(s); } </code></pre>
 

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