具有共同值的两个多图的交点

Question

#include <cstring>
#include <iostream>
#include <map>
#include <iterator>
#include <stdio.h>
#include <algorithm>
#include <stdlib.h>

//using namespace std;

template <class InputIterator1, class InputIterator2, class OutputIterator>

/* templet function to return common elements od two map  */

OutputIterator map_intersection ( InputIterator1 first1, InputIterator1 last1,
                                  InputIterator2 first2, InputIterator2 last2,
                                  OutputIterator result )
{
    while (first1!=last1 && first2!=last2)
    { 
        if (*first1<*first2) ++first1;
        else if (*first2<*first1) ++first2;
        else {  
            const char*abc= new char[15];
            const char*def= new char[15];
            /* Below code inserts the common element in result map */ 
            if(strcmp((first1->second.c_str()),(first2->second.c_str()))==0)
            {                                                                   
                result.insert(std::pair<std::string,std::string>(first1->first,first1->second));
                ++first1;
                ++first2;
            }
            else
            {
                ++first1;
                ++first2;  
            } 
        } 
    }
    return result;
}

using namespace std;

int main()
{
    std::multimap<string, string> m;
    std::multimap<string, string>::iterator it2;
    std::multimap<string, string> intersection;
    std::multimap<string, string> common;
    std::multimap<string, string> it3;

    cout <<"Making Map m "<<endl;
    m.insert(pair< string, string>("1 2"," 22 3" ));
    m.insert(pair< string, string>("1 2"," 21 4" ));
    m.insert(pair< string, string>("2 1"," 31 3" ));

    cout <<"Making Map c "<<endl;
    std::multimap<string, string> c;
    c.insert(pair< string, string>("1 2"," 22 3" ));
    c.insert(pair< string, string>("1 2"," 22 4" ));
    c.insert(pair< string, string>("2 1"," 31 3" ));

    cout << "Elements in common map are: " << endl;
    it3=map_intersection (m.begin(), m.end(), c.begin(), c.end(),common);

    cout << " am i out of the map_intersection loop " << endl;
    cout << " size of common map is : " << it3.size()<< endl;
    for(it2 =it3.begin(); it2!=it3.end();it2++)
    {   
        cout << "first common element is : " << endl;
        cout<< it2->first << " " << it2->second <<"  " << endl;
    }
    getchar();
}

我遇到了一个代码，它找到两个多重映射的交集，其值分配给不同的多重映射。我想有一个函数，它只检查两个multimaps的公共值，并将第一个multimap的键分配给交集。例如，

multimap 1:- 
1 2   22 3 
2 1   31 3   

multimap 2:- 
1 3   22 3 
2 1   31 3   

output:- 
2 1   31 3