How to get push_back to work in C++ program

Question

I'm working on a C++ assignment and having some issues with an error in regards to push_back. The error message reads:

No matching member function for call to 'push_back'.

The error occurs at the line that reads: book.push_back(name,number,email);

Here is the code:

//Program

#include <fstream>
#include <iostream>
#include <sstream>
#include <string>
#include <vector>

using namespace std;

// Declaring ye ol' phonebook structure //
struct phoneBook {
public:
    string name;
    int number;
    string email;
};

int main(){
    // Declaring the VECTOR of the Phonebook
    vector<phoneBook>book;
    string fileName;
    //reading the file
    cout <<"Enter file name to read contacts: ";
    cin >> fileName;

    std::string myline;
    std::ifstream infile(fileName);
        while (std::getline(infile, myline))
    {
        std::istringstream iss(myline);
        string name;
        int number;
        string email;
        if(!(iss >> name >> number >> email)) {break;}
        //pushing into vector
        book.push_back(name,number,email);
    }

//reading extra contacts from user
    while(true){
        int choice;
        cout << "Do you want to add extra contact? If so, type 1. If not, type 2 to exit:";
        cin >> choice;
        if(choice == 1){
            string name;
            int number;
            string email;
            cout << "Enter name: ";
            cin >> name;
            cout << "Enter number: ";
            cin >> number;
            cout << "Enter email: ";
            cin >> email;
            book.push_back(name,number,email);
        }
        else{
            break;
        }
    }

    //printing phone book
    cout << "Contacts are here: " << endl;
    for(int i=0;i<book.size();i++){
        cout << book[i].name << ""<<book[i].number<< "" << book[i].email << endl;
    }
    return 0;
}

`push_back` has a single parameter, easily verified by a reference. You pass three arguments. — chris, Mar 09 '17 at 02:01
Welcome to Stack Overflow. Please take the time to read [The Tour](http://stackoverflow.com/tour) and refer to the material from the [Help Center](http://stackoverflow.com/help/asking) what and how you can ask here. — πάντα ῥεῖ, Mar 09 '17 at 02:02
You have to create a new instance of phoneBook and `push_back` that single variable into your vector. — The Unknown Dev, Mar 09 '17 at 02:26

songyuanyao · Accepted Answer · 2017-03-09T03:16:05.627

5

Note that std::vector::push_back expects only one argument with type of the element of the vector, i.e. a phoneBook.

If you want the element (to be added) constructed from the arguments directly you can use emplace_back (since C++11) instead, e.g.

book.emplace_back(name,number,email);

or you can change it to use braced initializer (also since C++11):

book.push_back( {name, number, email} );

For pre-C++11 you can change it to construct a phoneBook explicitly.

book.push_back( phoneBook(name, number, email) );

edited Mar 09 '17 at 03:16

answered Mar 09 '17 at 02:01

songyuanyao

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Thanks, songyuanyao! I used "book.push_back ({name, number, email} ); and the program works. It's interesting, because I went to cplusplus.com and checked the format for a push_back and it does not mention having the curly braces. You saved me from hours of struggling with this. Thanks again! – John Smith Mar 10 '17 at 02:25
@JohnSmith Well, this is a feature introduced from C++11, not only used for `std::vector::push_back`. See [here](http://en.cppreference.com/w/cpp/language/list_initialization) (#(7)) for more details. – songyuanyao Mar 10 '17 at 02:29

How to get push_back to work in C++ program

1 Answers1