存储指向对象成员变量的指针

#include <iostream>

using namespace std;

template <typename Object, typename dataType>
class Collection
{
     public:

         Collection( dataType Object::*nMemberVariable )
         {
             memberVariable = nMemberVariable;
         }

         bool store( Object* o )
         {
              // check that o is not a NULL pointer & not already present in maps
              if ( o==NULL  ||  instanceVarMap.find(o->*memberVariable) != instanceVarMap.end() ) 
              { 
                   return false; 
              }

              instanceVarMap.insert( o->*memberVariable, o ); 
              return true;
         }

     private:  
         dataType Object::* memberVariable;
         std::map <dataType, Object*>     instanceVarMap;
};


struct FoodItem
{
    unsigned int ID;
    string name;
    double price;
};


int main()
{

    // I am attempting to store a pointer to an objects member variable
    // this is so I can create a custom container class(like a map or vector) that 
    // sorts its contents (which are FoodItem objects) according to their member variable values
    // so a container could sort all its elements according to a FoodItems ID value or name value

    Collection <FoodItem*> foodCol( &FoodItem::name );  

    string nNames[]           = {\"a\", \"b\", \"c\", \"d\"};
    double nPrices[]          = {1.1, 2.2, 3.3, 4.4};

    for (int i=0; i<4; i++)
    {
        FoodItem *f = new FoodItem() { i, nNames[i], nPrices[i] };
        foodCol.store( f );
    }

    // Note storing an ACTUAL object is possible with this class
    Collection <FoodItem*> foodCol( &FoodItem::name );  
    FoodItem f( 1, \"a\", 4 );
    foodCol.store( f ); 

    system(\"PAUSE\");
    return 0;   
}