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POhow to use "hash_map" on windows
 

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  1. POhow to use "hash_map" on windows
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    <p>I am trying to use the <strong>hash_map</strong> for my self-defined data structure <strong>Locations</strong>, which is in fact an array. When I tried to insert some value pairs, I got errors. But I don't know why.</p> <p>I am programming on Windows7 and I use VS 2010. Below is the minimum working set.</p> <pre><code> #include &lt;hash_map&gt; #include &lt;iostream&gt; using namespace std; #define HASH_NUM 8 struct Locations{ unsigned int loc[HASH_NUM]; }; //1. define the hash function struct hash_Locations{ size_t operator()(const Locations &amp; Loc) const { unsigned int seed = 131; // 31 131 1313 13131 131313 etc.. unsigned int hash = 0; char* str = (char*)Loc.loc; for (int i = 0; i &lt; HASH_NUM * 4; i ++) { hash = hash * seed + (*str++); } return (hash &amp; 0x7FFFFFFF); } }; //2. define less than function struct less_than{ bool operator()(const Locations &amp; x, const Locations &amp; y) const { for(int i = 0; i &lt; HASH_NUM; i ++){ if(x.loc[i] &lt; y.loc[i]) return true; } return false; } }; int main(){ hash_map&lt;Locations, unsigned int, hash_compare&lt;hash_Locations, less_than&gt; &gt; location_map; Locations x, y; for(int i = 0; i &lt; HASH_NUM; i ++){ x.loc[i] = i * 3; y.loc[i] = i * 2; } //error location_map.insert(pair&lt;Locations, unsigned int&gt;(x, 1)); location_map.insert(pair&lt;Locations, unsigned int&gt;(y, 2)); return 0; } </code></pre> <p>Edit: Here is the error report.</p> <pre><code> 1&gt;------ Build started: Project: hash_map, Configuration: Debug Win32 ------ 1&gt; hash_map.cpp 1&gt;d:\program files (x86)\microsoft visual studio 10.0\vc\include\xhash(854): error C2664: 'bool stdext::hash_compare&lt;_Kty,_Pr&gt;::operator ()(const _Kty &amp;,const _Kty &amp;) const' : cannot convert parameter 1 from 'const Locations' to 'const hash_Locations &amp;' 1&gt; with 1&gt; [ 1&gt; _Kty=hash_Locations, 1&gt; _Pr=less_than 1&gt; ] 1&gt; Reason: cannot convert from 'const Locations' to 'const hash_Locations' 1&gt; No user-defined-conversion operator available that can perform this conversion, or the operator cannot be called 1&gt; d:\program files (x86)\microsoft visual studio 10.0\vc\include\xhash(849) : while compiling class template member function 'std::pair&lt;_Ty1,_Ty2&gt; std::_Hash&lt;_Traits&gt;::_Insert(const std::pair&lt;const _Kty,_Ty&gt; &amp;,std::_List_iterator&lt;_Mylist&gt;)' 1&gt; with 1&gt; [ 1&gt; _Ty1=std::_List_iterator&lt;std::_List_val&lt;std::pair&lt;const Locations,unsigned int&gt;,std::allocator&lt;std::pair&lt;const Locations,unsigned int&gt;&gt;&gt;&gt;, 1&gt; _Ty2=bool, 1&gt; _Traits=std::_Hmap_traits&lt;Locations,unsigned int,stdext::hash_compare&lt;hash_Locations,less_than&gt;,std::allocator&lt;std::pair&lt;const Locations,unsigned int&gt;&gt;,false&gt;, 1&gt; _Kty=Locations, 1&gt; _Ty=unsigned int, 1&gt; _Mylist=std::_List_val&lt;std::pair&lt;const Locations,unsigned int&gt;,std::allocator&lt;std::pair&lt;const Locations,unsigned int&gt;&gt;&gt; 1&gt; ] 1&gt; d:\program files (x86)\microsoft visual studio 10.0\vc\include\hash_map(91) : see reference to class template instantiation 'std::_Hash&lt;_Traits&gt;' being compiled 1&gt; with 1&gt; [ 1&gt; _Traits=std::_Hmap_traits&lt;Locations,unsigned int,stdext::hash_compare&lt;hash_Locations,less_than&gt;,std::allocator&lt;std::pair&lt;const Locations,unsigned int&gt;&gt;,false&gt; 1&gt; ] 1&gt; c:\documents and settings\daihuichen\桌面\hash_map\hash_map.cpp(42) : see reference to class template instantiation 'stdext::hash_map&lt;_Kty,_Ty,_Tr&gt;' being compiled 1&gt; with 1&gt; [ 1&gt; _Kty=Locations, 1&gt; _Ty=unsigned int, 1&gt; _Tr=stdext::hash_compare&lt;hash_Locations,less_than&gt; 1&gt; ] 1&gt;d:\program files (x86)\microsoft visual studio 10.0\vc\include\xhash(857): error C2664: 'bool stdext::hash_compare&lt;_Kty,_Pr&gt;::operator ()(const _Kty &amp;,const _Kty &amp;) const' : cannot convert parameter 1 from 'const Locations' to 'const hash_Locations &amp;' 1&gt; with 1&gt; [ 1&gt; _Kty=hash_Locations, 1&gt; _Pr=less_than 1&gt; ] 1&gt; Reason: cannot convert from 'const Locations' to 'const hash_Locations' 1&gt; No user-defined-conversion operator available that can perform this conversion, or the operator cannot be called ========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ========== </code></pre>
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