map如何按value来排序------用带pair的vector吧

#include <iostream>
#include <string>
#include <utility> // pair
#include <vector>
#include <algorithm>
using namespace std;

bool comp(const pair<int, string> &a, const pair<int, string> &b)
{
return a.second < b.second;
}

int main()
{
using namespace std;

vector<pair<int, string> > vec;

vec.push_back(make_pair<int, string>(15, "def"));
vec.push_back(make_pair<int, string>(14, "abcd"));
vec.push_back(make_pair<int, string>(16, "abc"));

sort(vec.begin(), vec.end(), comp);

vector<pair<int, string> >::iterator it;

for(it = vec.begin(); it != vec.end(); ++it)
{
cout << it->second << endl;
}

return 0;
}