How to specifiy comparison for pair?

Question

There is a pair

pair <string, int> myPair;

I have a vector of myPair objects. I need to convert it to a min-heap using make_heap on the second value of pair i.e. the integer. How can I do that? I am not sure on how to define the comparison operations.

I know I need something like this for heap to operate. But not sure where to put it:

bool operator< (const Pair& p1, const Pair& p2) const 
{ 
    return p1.second < p2.second;
}

Solution

Well, make_heap has an overload that takes an extra comparision operator, soo...

// somewhere in global namespace
typedef std::pair<std::string, int> myPair_type;

struct mypair_comp{
  bool operator()(myPair_type const& lhs, myPair_type const& rhs){
    return lhs.second < rhs.second;
  }
};

// somewhere at your callside
make_heap(first,last,mypair_comp());

Comments

[John Zwinck]

Pretty much this, though the lhs & rhs arguments need to be of some type, so either myPair should be a typedef (rather than a variable), or some typedef should be created.

[Xeo]

@John Zwinck: Woops, totally saw that as a typedef, lol.. Edited. :)