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Undefined operator link >>

I am trying to work with operator overloading, my header file consists of:

#ifndef PHONENUMBER_H
#define PHONENUMBER_H

#include<iostream>
#include<string>
using namespace std;

class Phonenumber
{
    friend ostream &operator << ( ostream&, const Phonenumber & );
    friend istream &operator >> ( istream&, Phonenumber & );
private:
    string areaCode;
    string exchange;
    string line;

};

#endif // PHONENUMBER_H

And class definition

//overload stream insertion and extraction operators
//for class Phonenumber
#include <iomanip>
#include "Phonenumber.h"
using namespace std;
//overloades stram insertion operator cannot be a member function
// if we would like to invoke it with
//cout<<somePhonenumber
ostream &operator << ( ostream &output, const Phonenumber &number)
{

    output<<"("<<number.areaCode<<")"
     <<number.exchange<<"-"<<number.line;
    return output;

}//end function opertaor <<

istream &operator >> ( istream &input, Phonenumber &number)
{
    input.ignore(); //skip (
    input>>setw(3)>>number.areaCode;//input areacode
    input.ignore(2);//skip ) and space
    input>>setw(3)>>number.exchange;//input exchange
    input.ignore();//skip -
    input>>setw(4)>>number.line;//input line
    return input;
}

a call made through main,

#include <iostream>
#include"Phonenumber.h"
using namespace std;

int main()
{
    Phonenumber phone;
    cout<<"Enter number in the form (123) 456-7890:"<<endl;
    //cin>> phone invokes operator >> by implicitly issuing the non-member function call operator>>(cin,phone)
    cin >> phone;
    //cout<< phone invokes operator << by implicitly issuing the non-member function call operator>>(cout,phone)
    cout << phone<<endl;
    return 0;
}

but compilation shows me a compiler error: undefined reference to 'operator>>(std:istream&, Phonenumber&)' Can someone help me solve this error?

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1 answer

The error "undefined reference to ..." is a linker error. Your code is fine, but you don’t link all the source files with the final product, Phonenumber.cpp(or whatever you call it) is not taken into account.

In my system

$ ls
Phonenumber.cpp Phonenumber.h main.cpp
$ g ++ main.cpp
/tmp/cce0OaNt.o: In function `main ':
main.cpp:(.text+0x40): undefined reference to `operator>>(std::basic_istream<char, std::char_traits<char> >&, Phonenumber&)'
main.cpp:(.text+0x51): undefined reference to `operator<<(std::basic_ostream<char, std::char_traits<char> >&, Phonenumber const&)'
collect2: ld returned 1 exit status

, Phonenumber.cpp . ,

$ g++ main.cpp Phonenumber.cpp
$ ./a.out
Enter number in the form (123) 456-7890:
(555) 555-1234
(555)555-1234

.cpp , . .

Source code ---compile--> Object files ---link--> Application

Phonenumber.cpp ----+
                    |---> Phonenumber.o ---+
                +---+                      |
                |                          |
Phonenumber.h --+                          +--> a.out
                |                          |
                +---+                      |
                    |---> main.o ----------+
main.cpp -----------+
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