CODEWITHSUNDEEP
c++dictionary
XDProgrammer
XDProgrammer

Reputation: 861

How to access map?

I am not sure how to access the map inside the struct Student Some examples that I look up says -> first ->second but this does not compile.

How I can access map inside the struct? or the overloading of the operator is wrong?

the error says ‘->’ has non-pointer type 

struct Student{
      string id;
      map<string, double> scores;
    };


ostream& operator<<(ostream& os, const Student& g){
    return os << g.id << '\n' <<  g.scores->first << '\n' << g.scores->second ;
}

istream& operator >>(istream& is, Student& g){
    return is >> g.id >> g.scores->first >> g.scores->second;
}


int main() {

    vector<Student> g_vec;
    Student grades;

    while(cin >> gd)
        g_vec.push_back(grades);

    for (auto& g : g_vec)
        cout << g << endl;

    }

Upvotes: 0

Views: 253

Answers (2)

MKR Harsha
MKR Harsha

Reputation: 115

I haven't understood the problem. It's more elaborate if you show us the sample output. sorry if I am wrong, I am unable to find when you are going to stop reading data. . ?

You need to use pair to insert to map and to traverse you should use iterator. Hope this helps:

ostream& operator<<(ostream& os, const Student& g){
      //here you need to write for loop to traverse the entire map. I am printing only last ele. .  
    map<string,double>::const_iterator myit = g.scores.end();
    os << g.id << '\n' <<  myit->first << '\n' << myit->second ;
    return os;
}

istream& operator >>(istream& is, Student& g){
    pair<string,double> mypair;
    is >> g.id >> mypair.first >> mypair.second;
    g.scores.insert(mypair);
    return is;
}

Upvotes: 0

Dimitri Mockelyn
Dimitri Mockelyn

Reputation: 1545

The main difference between . and ->is the type of objet you have at the beginning. Use .when you have your object, and ->when you have a pointer to your object

If you define a Student this way

Student erik = ...

You'll get erik's id like this :

erik.id

If you define erik like this :

Student* erik = ...

you'll get his id like this :

erik->id

And that's what the error mean

But you have another problem, since firstand secondare not defined for a map, but for a map element. You'll need to iterate through the map in order to do what you want. I'd guess something like this would be better

os << g.id << '\n'
for (auto& it : g.scores) {
    os<< it.first << it.second << '\n' ;
}

Upvotes: 1

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