C ++：Pop_back配对向量

Question

I have a paired vector like this

 vector <pair<int , string> > Names;    

I put data in it this way:

cin>>taxi>>Ar_taxis>>Ar_mathiton;

        for(j=0;j<Ar_mathiton;j++)
        {
            cin>>Ar_Mitroou>>Onoma;
            Names.push_back(make_pair(Ar_Mitroou,Onoma));

        }

I sort it and then i print it:

  for(j=0;j<Ar_mathiton;j++)
        {
            cout<<Names[i].first<<" "<<Names[i].second<<endl;
           Names.pop_back();
        }

There's a problem with my pop_back() , it doesn't delete the set of pair. I don't know if there's another command to do it. Thanks.

[edit] the whole code

  cin>>Ar_taxeon;

for(i=0;i<Ar_taxeon;i++)
{
    cin>>taxi>>Ar_taxis>>Ar_mathiton;

        for(j=0;j<Ar_mathiton;j++)
        {
            cin>>Ar_Mitroou>>Onoma;
            Names.push_back(make_pair(Ar_Mitroou,Onoma));

        }

        sort(Names.begin(),Names.end());

        cout<<taxi<<Ar_taxis<<endl;
        for(j=0;j<Ar_mathiton;j++)
        {
            cout<<Names[i].first<<" "<<Names[i].second<<endl;
           Names.pop_back();
        }

}

Answer 1

Consider following changes:

change name of variable i inside loop into j

and you can call Names.clear() after cout, instead of Names.popBack():

so your final code will be:

#include <iostream>
#include <vector>
using namespace std;
int main(){
vector <pair<int , string> > Names;

int Ar_mathiton,Ar_Mitroou;
string Onoma;
cin>>Ar_mathiton;

for(int j=0;j<Ar_mathiton;j++)
{
    cin>>Ar_Mitroou>>Onoma;
    Names.push_back(make_pair(Ar_Mitroou,Onoma));

}
for(int j=0;j<Ar_mathiton;j++)
{
    cout<<Names[j].first<<" "<<Names[j].second<<endl;

}
Names.clear();

return 0;
}

Answer 2

There's a variety of problems with the example you posted.

The first one is that you are iterating over the list using j , but accessing Names with the index of i . However, even if you fixed that you would get a crash because you are iterating forward through the vector, but popping off the back , this means that you will eventually get an out-of-range error as the iterating index passes over the length of the list.

If you want to remove all items in one go, you should just call Names.clear() .

Additionally, it's bad form to be using C++ and not using the C++ way of iterating through lists.

Consider changing your second loop to the following:

for (auto& name : Names)
{
    cout << Names[j].first << " " << Names[j].second << endl;
}

Then finally, call this:

Names.clear();