Sorting for equal_range()

[Paul McKenzie]

and is it possible to write more than one comparison method with different comparison criteria?

A struct can basically do anything you want it to do. All you would need is to pass which criteria you want to use when you construct it.

struct MyPred
{
    std::string x;
    std::string y;
    int sorting_criteria;

    MyPred(const std::string& x, const std::string& y,
                             int crit = 0): x(x), y(y), sorting_criteria(crit) {}

    bool operator()(const MyPred& p1, MyPred& p2) const
    {
           switch( sorting_criteria ) 
           { 
                   case 0:
                           return SortThisWay(p1, p2);
                   case1:
                           return SortThatWay( p1, p2);
                   case 2:
                           return SortAThirdWay( p1, p2);
            }
            return false;
        }
//...
};

That is just a rough outline.

Regards,

Paul McKenzie