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POC++ boost shared_ptr as a hash_map key
 

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  1. POC++ boost shared_ptr as a hash_map key
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    <p>I'm making a neural network and wanted to use a hash_map to keep weight references for output neurons for each neuron:</p> <pre><code>class Neuron; //forward declaration was there (sorry I forgot to show it earlier) typedef double WEIGHT; typedef stdext::hash_map&lt;boost::shared_ptr&lt;Neuron&gt;,WEIGHT&gt; NeuronWeightMap; class Neuron { private: NeuronWeightMap m_outputs; //... public: Neuron(); ~Neuron(); //... WEIGHT GetWeight(const boost::shared_ptr&lt;Neuron&gt;&amp; neuron) const { NeuronWeightMap::const_iterator itr = m_outputs.find(neuron); if( itr != m_outputs.end() ) { return itr-&gt;second; } return 0.0f; } }; </code></pre> <p>I realize that I can't use the boost::shared_ptr as the key of a stdext::hash_map, so what would be another suggestion? Are there any work-arounds or is the only option to use a different key or maybe switch to an std::map? Thanks!</p> <p>Here is the errors:</p> <pre><code>1&gt;c:\program files (x86)\microsoft visual studio 8\vc\include\xhash(61) : error C2440: 'type cast' : cannot convert from 'const boost::shared_ptr&lt;T&gt;' to 'size_t' 1&gt; with 1&gt; [ 1&gt; T=Neuron 1&gt; ] 1&gt; No user-defined-conversion operator available that can perform this conversion, or the operator cannot be called 1&gt; c:\program files (x86)\microsoft visual studio 8\vc\include\xhash(99) : see reference to function template instantiation 'size_t stdext::hash_value&lt;_Kty&gt;(const _Kty &amp;)' being compiled 1&gt; with 1&gt; [ 1&gt; _Kty=boost::shared_ptr&lt;Neuron&gt; 1&gt; ] 1&gt; c:\program files (x86)\microsoft visual studio 8\vc\include\xhash(98) : while compiling class template member function 'size_t stdext::hash_compare&lt;_Kty,_Pr&gt;::operator ()(const _Kty &amp;) const' 1&gt; with 1&gt; [ 1&gt; _Kty=boost::shared_ptr&lt;Neuron&gt;, 1&gt; _Pr=std::less&lt;boost::shared_ptr&lt;Neuron&gt;&gt; 1&gt; ] 1&gt; c:\program files (x86)\microsoft visual studio 8\vc\include\hash_map(80) : see reference to class template instantiation 'stdext::hash_compare&lt;_Kty,_Pr&gt;' being compiled 1&gt; with 1&gt; [ 1&gt; _Kty=boost::shared_ptr&lt;Neuron&gt;, 1&gt; _Pr=std::less&lt;boost::shared_ptr&lt;Neuron&gt;&gt; 1&gt; ] 1&gt; c:\program files (x86)\microsoft visual studio 8\vc\include\xhash(119) : see reference to class template instantiation 'stdext::_Hmap_traits&lt;_Kty,_Ty,_Tr,_Alloc,_Mfl&gt;' being compiled 1&gt; with 1&gt; [ 1&gt; _Kty=boost::shared_ptr&lt;Neuron&gt;, 1&gt; _Ty=common_ns::WEIGHT, 1&gt; _Tr=stdext::hash_compare&lt;boost::shared_ptr&lt;Neuron&gt;,std::less&lt;boost::shared_ptr&lt;Neuron&gt;&gt;&gt;, 1&gt; _Alloc=std::allocator&lt;std::pair&lt;const boost::shared_ptr&lt;Neuron&gt;,common_ns::WEIGHT&gt;&gt;, 1&gt; _Mfl=false 1&gt; ] 1&gt; c:\program files (x86)\microsoft visual studio 8\vc\include\hash_map(90) : see reference to class template instantiation 'stdext::_Hash&lt;_Traits&gt;' being compiled 1&gt; with 1&gt; [ 1&gt; _Traits=stdext::_Hmap_traits&lt;boost::shared_ptr&lt;Neuron&gt;,common_ns::WEIGHT,stdext::hash_compare&lt;boost::shared_ptr&lt;Neuron&gt;,std::less&lt;boost::shared_ptr&lt;Neuron&gt;&gt;&gt;,std::allocator&lt;std::pair&lt;const boost::shared_ptr&lt;Neuron&gt;,common_ns::WEIGHT&gt;&gt;,false&gt; 1&gt; ] 1&gt; FILE_PATH_REMOVED\neuralnet.h(21) : see reference to class template instantiation 'stdext::hash_map&lt;_Kty,_Ty&gt;' being compiled 1&gt; with 1&gt; [ 1&gt; _Kty=boost::shared_ptr&lt;Neuron&gt;, 1&gt; _Ty=common_ns::WEIGHT 1&gt; ] 1&gt;NeuralNet.cpp 1&gt;c:\program files (x86)\microsoft visual studio 8\vc\include\xhash(61) : error C2440: 'type cast' : cannot convert from 'const boost::shared_ptr&lt;T&gt;' to 'size_t' 1&gt; with 1&gt; [ 1&gt; T=Neuron 1&gt; ] 1&gt; No user-defined-conversion operator available that can perform this conversion, or the operator cannot be called 1&gt; c:\program files (x86)\microsoft visual studio 8\vc\include\xhash(99) : see reference to function template instantiation 'size_t stdext::hash_value&lt;_Kty&gt;(const _Kty &amp;)' being compiled 1&gt; with 1&gt; [ 1&gt; _Kty=boost::shared_ptr&lt;Neuron&gt; 1&gt; ] 1&gt; c:\program files (x86)\microsoft visual studio 8\vc\include\xhash(98) : while compiling class template member function 'size_t stdext::hash_compare&lt;_Kty,_Pr&gt;::operator ()(const _Kty &amp;) const' 1&gt; with 1&gt; [ 1&gt; _Kty=boost::shared_ptr&lt;Neuron&gt;, 1&gt; _Pr=std::less&lt;boost::shared_ptr&lt;Neuron&gt;&gt; 1&gt; ] 1&gt; c:\program files (x86)\microsoft visual studio 8\vc\include\hash_map(80) : see reference to class template instantiation 'stdext::hash_compare&lt;_Kty,_Pr&gt;' being compiled 1&gt; with 1&gt; [ 1&gt; _Kty=boost::shared_ptr&lt;Neuron&gt;, 1&gt; _Pr=std::less&lt;boost::shared_ptr&lt;Neuron&gt;&gt; 1&gt; ] 1&gt; c:\program files (x86)\microsoft visual studio 8\vc\include\xhash(119) : see reference to class template instantiation 'stdext::_Hmap_traits&lt;_Kty,_Ty,_Tr,_Alloc,_Mfl&gt;' being compiled 1&gt; with 1&gt; [ 1&gt; _Kty=boost::shared_ptr&lt;Neuron&gt;, 1&gt; _Ty=common_ns::WEIGHT, 1&gt; _Tr=stdext::hash_compare&lt;boost::shared_ptr&lt;Neuron&gt;,std::less&lt;boost::shared_ptr&lt;Neuron&gt;&gt;&gt;, 1&gt; _Alloc=std::allocator&lt;std::pair&lt;const boost::shared_ptr&lt;Neuron&gt;,common_ns::WEIGHT&gt;&gt;, 1&gt; _Mfl=false 1&gt; ] 1&gt; c:\program files (x86)\microsoft visual studio 8\vc\include\hash_map(90) : see reference to class template instantiation 'stdext::_Hash&lt;_Traits&gt;' being compiled 1&gt; with 1&gt; [ 1&gt; _Traits=stdext::_Hmap_traits&lt;boost::shared_ptr&lt;Neuron&gt;,common_ns::WEIGHT,stdext::hash_compare&lt;boost::shared_ptr&lt;Neuron&gt;,std::less&lt;boost::shared_ptr&lt;Neuron&gt;&gt;&gt;,std::allocator&lt;std::pair&lt;const boost::shared_ptr&lt;Neuron&gt;,common_ns::WEIGHT&gt;&gt;,false&gt; 1&gt; ] 1&gt; FILE_PATH_REMOVED\neuralnet.h(21) : see reference to class template instantiation 'stdext::hash_map&lt;_Kty,_Ty&gt;' being compiled 1&gt; with 1&gt; [ 1&gt; _Kty=boost::shared_ptr&lt;Neuron&gt;, 1&gt; _Ty=common_ns::WEIGHT 1&gt; ] 1&gt;Generating Code... </code></pre>
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