sort method of a multimap

[Rodolfo Lima]

Is there a way to guarantee that the values inside a multimap are sorted in a certain way? I don't mean just sorting the keys, but values mapped to the same key also sorted by a functor (function object) or anything else? Even though I can retrieve the value_comp functor, I cannot set it because it's defined within the multimap class. This default value_comp just sorts the keys. What I really want is that equal_range returns iterators to sorted values according to my compare functor, but I couldn't find a way to accomplish this. The the values returned by the iterators aren't sorted in any special way that I can contro. Thanks for any help, rod

[Joaquin M Lopez Munoz]

Well, you can have sort of what you're after by using multiset instead of multimap like the following: Suppose your multimap is originally defined as:

std::multimap<type_a,type_b>

So, define a struct holding the two parts of the multimap:

struct pair_ab
{
type_a first; // names of members à la std::pair
type_b second;

bool operator<(const pair_ab& x)const
{
if(first<x.first)return true;
if(x.first<first)return false;
return second<x.second;
}
};

and replace your multimap with

std::multiset<pair_ab>

Now, this multiset really behaves as a multimap on type_a with the added feature that elements with equivalent first members are further sorted by second. Please report back if this works. Good luck. Joaquín M López Muñoz Telefónica, Investigación y Desarrollo