compare two multimaps c++

Question

I have two multimaps.i would like to create a new multimap which has the common key-value pairs in the given those two multimaps:

for eg:

#include <iostream>
#include <string>
#include <map>
using namespace std;

int main ()
{


multimap<std::string, std::string> m;
multimap<std::string, std::string> n;


m.insert(multimap<string,string>::value_type("1-2","1-1"));
m.insert(multimap<string,string>::value_type("1-2","1-2"));
m.insert(multimap<string,string>::value_type("1-2","1-3"));
m.insert(multimap<string,string>::value_type("1-2","1-4"));
m.insert(multimap<string,string>::value_type("1-3","2-1"));
m.insert(multimap<string,string>::value_type("1-3","21-1"));
m.insert(multimap<string,string>::value_type("1-3","21-2"));

n.insert(multimap<string,string>::value_type("1-2","1-1"));
n.insert(multimap<string,string>::value_type("1-2","1-2"));
n.insert(multimap<string,string>::value_type("1-2","1-5"));
n.insert(multimap<string,string>::value_type("1-2","1-7"));
n.insert(multimap<string,string>::value_type("1-3","2-1"));
n.insert(multimap<string,string>::value_type("1-3","21-4"));
n.insert(multimap<string,string>::value_type("1-3","21-2"));

cout<<"multimap of m"<<endl;
cout<<"--------------"<<endl;
for(multimap<string,string>::iterator i=m.begin();i!=m.end();i++)
cout <<i->first<<" "<<i->second<<endl;
cout<<"multimap of n"<<endl;
cout<<"--------------"<<endl;
for(multimap<string,string>::iterator i=n.begin();i!=n.end();i++)
cout <<i->first<<" "<<i->second<<endl;

}

this results in :

multimap of m
--------------
1-2 1-1
1-2 1-2
1-2 1-3
1-2 1-4
1-3 2-1
1-3 21-1
1-3 21-2
multimap of n
--------------
1-2 1-1
1-2 1-2
1-2 1-5
1-2 1-7
1-3 2-1
1-3 21-4
1-3 21-2

i want to create a new multimap: which has the below elements:

1-2 1-1
1-2 1-2
1-3 2-1
1-3 21-2

EDIT:

also is there a way where i can delete the common elements( pair) from both the maps.

Answer 1

Use the std::set_intersection function template from <algorithm>

std::multimap<T1, T2> newMap;
std::set_intersection(map1.begin(), map1.end(), 
                      map2.begin(), map2.end(), 
                      std::inserter(newMap, newMap.begin());

Edit Yeah, apparently this doesn't work for a multimap as it would for a map. I suggest the following:

std::multimap<T1, T2> newMap;
std::vector<std::multimap<T1, T2>::value_type> v1(map1.begin(), map1.end());
std::sort(v1.begin(), v1.end());
std::vector<std::multimap<T1, T2>::value_type> v2(map2.begin(), map2.end());
std::sort(v2.begin(), v2.end());
std::set_intersection(v1.begin(), v1.end(), 
                      v2.begin(), v2.end(), 
                      std::inserter(newMap, newMap.begin());