c++ - how to compare two std::set?

Question

I do such comparison of two std::set

#include <cstdlib>
#include <cstdio>
using namespace std;

#include <vector>
#include <set>


int main(int argc, char** argv)
{
    int myints1[]= {10,20,30,40,50};
    int myints2[]= {50,40,30,20,10};
    std::set<int> s1 (myints1,myints1+5);
    std::set<int> s2(myints2,myints2+5);
    if(s1==s2){
        printf("sets: true");
    }else printf("sets: false");
    std::set<int>::iterator it2=s2.begin();
    for(std::set<int>::iterator it1=s1.begin();it1!=s1.end();it1++){
                printf("
s1: %d  s2: %d",*it1,*it2);
        it2++;
    }
}

output:

sets: true
s1: 10  s2: 10
s1: 20  s2: 20
s1: 30  s2: 30
s1: 40  s2: 40
s1: 50  s2: 50

Question:

Is this the right way to do it? Or is any other (special) way of comparing two sets?

question from:https://stackoverflow.com/questions/16182958/how-to-compare-two-stdset

Answer 1

Yes, operator== is correctly defined for all standard containers (except the unordered containers - based on 23.2.5.2 of the standard), and will generally do a lexicographic comparison. See for example here. The relevant quote:

Checks if the contents of lhs and rhs are equal, that is, whether lhs.size() == rhs.size() and each element in lhs has equivalent element in rhs at the same position.

Since std::set is an ordered container, any set with the same size and same elements (given the comparators are the same) will necessarily have them in the same position, hence will compare equal.