Question

How can I write my own hash and equity operator for an unordered map so that I can use a char * instead of a std::string as a key?

Answer 1

class PtrStr
{
    protected:
        const char *m_pcStr;
        const int m_nSize;

    public:
        PtrStr(const char *pcStr, int nSize) : m_pcStr(pcStr), m_nSize(nSize) {}
        ~PtrStr() {};

        const char *GetStr() const { return m_pcStr; }
        const int GetSize() const { return m_nSize; }
};

namespace std
{ 
    namespace tr1
    { 
        template<> struct hash<PtrStr>
        {
            std::size_t operator()(PtrStr const &key) const
            {
                return MyHashMethod(key);
            }
        };
    }

    template<> struct equal_to<PtrStr>
    {
        bool operator()(const PtrStr &keyA, const PtrStr &keyB) const
        {
            return (strcmp(const_cast<PtrStr &>(keyA).GetStr(), const_cast<PtrStr &>(keyB).GetStr()) == 0);
            return (strcmp(keyA.GetStr(), keyB.GetStr()) == 0);
        }
    };
}

typedef std::tr1::unordered_map<PtrStr, int> unorderedCharMap;
typedef std::tr1::unordered_map<PtrStr, int>::iterator unorderedCharMapItr;