How to store structor as key in the stdext::hash_map

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C++

#include "hash_map"

struct MyStruct
{
    MyStruct( const void* pInfo, UINT uNumber ) : m_pInfo( pInfo ),
                                                  m_uNumber( uNumber )
    {
    }
    friend bool operator< ( const MyStruct& stKey1_i, const MyStruct& stKey2_i )
    {
        if( stKey1_i.m_pInfo == stKey2_i.m_pInfo )
        {
            return stKey1_i.m_uNumber < stKey2_i.m_uNumber;
        }
        else
        {
            return stKey1_i.m_pInfo < stKey2_i.m_pInfo;
        }
    }
    const void* m_pInfo;
    UINT m_uNumber;
};

int _tmain(int argc, _TCHAR* argv[])
{
    typedef stdext::hash_map< const MyStruct, int > MyMap;
    MyMap map;
    MyStruct mystructObj1 = MyStruct( new char[20], 10 );
    map[ mystructObj1 ] = 500;
    return 0;
}

After compiling the above code i got following error message
error C2440: 'type cast' : cannot convert from 'const MyStruct' to 'size_t'

How to solve this?