Sample C++ class implementation of functor/comparer object

comparer.cpp

#include <string>

template <class T>
struct Comparer
{
	Comparer(void){}
	~Comparer(){}

	// const & - not modifying compared items and not copying them
	int operator () (const T & a, const T & b) const
	{
		return ( (a < b) ? -1 : ( (a > b) ? 1 : 0) );
	}

	int operator () (const T * a, const T * b) const
	{
		return ( (*a < *b) ? -1 : ( (*a > *b) ? 1 : 0) );
	}
};

template <>
struct Comparer <std::string>
{
	Comparer(void){}
	~Comparer(){}

	// const & - we do not want to make a copy or modify of the compared strings
	int operator () (const std::string & a, const std::string & b) const
	{
		return a.compare(b);
	}
};