stuff about set multiset map multimap

　　A lot of interviewers like to ask the candidates the difference between set and multiset(map and multimap).What does multi actually mean?Multi-container could have duplicate element.Check the code below.

 /*********************************************
 Author:Zhou You
 Time:2014.09.06
 Feature:comparison of containers such as set,multiset,map and multimap.
 *********************************************/

 #include <iostream>
 #include <string>
 #include <map>
 #include <set>

 using namespace std;

 class setdata
 {
 public:
     setdata():
         data_(){
     }
     setdata(int data):
         data_(data){
     }
     ~setdata(){}

     bool operator<(const setdata &data) const{
         return data_<data.GetData();
     }

     int GetData() const{
         return data_;
     }

 private:
     int data_;
 };

 struct mapcmp
 {
     bool operator()(const int &data1,const int &data2){
         return data1<data2;
     }
 };

 set<setdata> set_int;
 multiset<setdata> multiset_int;
 map<int,string,mapcmp> map_intstr;
 multimap<int,string,mapcmp> multimap_intstr;

 int main()
 {
     //for set
     set_int.insert(setdata());
     set_int.insert(setdata());
     set_int.insert(setdata());
     set_int.insert(setdata());

     cout<<"output set container data"<<endl;
     for(set<setdata>::iterator iter = set_int.begin();iter!=set_int.end();++iter){
         cout<<iter->GetData()<<" ";
     }
     cout<<endl<<endl;

     //for multiset
     multiset_int.insert(setdata());
     multiset_int.insert(setdata());
     multiset_int.insert(setdata());//insert 20 again.
     multiset_int.insert(setdata());
     multiset_int.insert(setdata());

     cout<<"output multiset container data"<<endl;
     for(set<setdata>::iterator iter = multiset_int.begin();iter!=multiset_int.end();++iter){
         cout<<iter->GetData()<<" ";
     }
     cout<<endl<<endl;

     //for map
     map_intstr.insert(pair<int,string>(,"chen"));
     map_intstr.insert(pair<int,string>(,"wang"));
     map_intstr.insert(pair<int,string>(,"wu"));
     map_intstr.insert(pair<int,string>(,"tang"));

     for(map<int,string>::iterator iter = map_intstr.begin();iter!=map_intstr.end();++iter){
         cout<<iter->second<<" ";
     }
     cout<<endl<<endl;

     //for multimap
     multimap_intstr.insert(pair<int,string>(,"chen"));
     multimap_intstr.insert(pair<int,string>(,"wang"));
     multimap_intstr.insert(pair<int,string>(,"wu"));
     multimap_intstr.insert(pair<int,string>(,"wu"));//insert wu again.
     multimap_intstr.insert(pair<int,string>(,"tang"));

     for(map<int,string>::iterator iter = multimap_intstr.begin();iter!=multimap_intstr.end();++iter){
         cout<<iter->second<<" ";
     }
     cout<<endl;

     return ;
 }

　　In both map and set,I define compare function myself.