打印出键为结构变量的映射键值C ++

Question

struct cno{
    int sub;
};

A struct is taken as a key variable in map.

map<cno,int> s;
struct cno k;

I am trying to print the key value like this.

for(map<cno,int>::iterator it = s.begin();it!=s.end();it++){
    cout<<it->first<<endl;
}//Error

I have already overloaded < operator to compare the key values.

Answer 1

All you need to do is ( it->first.sub )

for(map<cno,int>::iterator it = s.begin();it!=s.end();it++){
    cout<<it->first.sub<<endl;
}

Why? first is of type cno , and you need to access desired element.

If you have implemented overload operator << for this, please give the code here.

Answer 2

This is how you overload an operator:

ostream& operator<<(ostream& out,cno &c){
    out<<c.sub<<endl;
    return out;
}

You need to overload operators in order to print,compare or process an element of an user defined object.Here we have to overload ostream object in order to print your user defined object.