CODEWITHSUNDEEP
c++classdictionary
user3813318
user3813318

Reputation: 31

Adding a class to a map

I am trying to add a class object to a map, this is what I have:

#include<vector>
#include<map>
#include<stdio.h>
#include<string>
#include<iostream>

using namespace std;

class Student{
    int PID;
    string name;
    int academicYear;
public:
    Student(int, string, int);
};

Student::Student (int P, string n, int a) {
    PID = P;
    name = n;
    academicYear = a;
}

void createStudent(map<string, Student>);

int main(int argc, char** argv){

    map <string, Student> studentList;

    createStudent(studentList);
}


void createStudent(map<string, Student> studentList){

    int PID;
    string name;
    int academicYear;

    cout << "Add new student-\nName: ";
    getline(cin, name);
    cout << "PID: ";
    cin >> PID;
    cout << "Academic year: ";
    cin >> academicYear;

    Student newstud (PID, name, academicYear);

    studentList[name] = newstud;  //this line causes the error: 
                                  //no matching function for call to 
                                  //'Student::Student()'
}

I don't understand why the constructor function is being called there, I thought newstud would already have been constructed from the previous line. Can anyone explain what is happening when I try to add newstud to the map?

Upvotes: 0

Views: 193

Answers (2)

P0W
P0W

Reputation: 47784

  • Problem 1st

std::map::operator[] will insert new element into container if its not present, using default constructor, which in your case is not present and will probably doesn't make sense even if you provide one.

So use std::map::insert for such scenario

  • Problem 2nd

Even if you successfully insert using studentList.insert(std::make_pair(name, newstud)); its not going to reflect changes in original map studentList in main ( ) unless you use a reference type, in function definition & declaration of createStudent

So use 

void createStudent(map<string, Student>& );

Upvotes: 2

twenty04
twenty04

Reputation: 116

In order to add entries using the function, you should make your parameter studentList pass by reference.

And instead of 

studentList[name] = newstud;

use: 

studentList.insert(std::make_pair(name, newstud));

Just a suggestion, though.

Upvotes: 1

Related Questions