Question

I am working on a C++ assignment for class that wants me to overload the “>>” operator. I am encountering errors linking in both Visual Studio 2005 and Xcode 3.2.2. The C++ code is separated into a few files. The prototypes are stored in overload.h, the implementations are stored in overload.cpp, and main() is in overloadtester.cpp (although I have not been able to put anything related to this new overloaded operator in main yet because of the error. below is the code I added before I started getting the errors (listed below)

// overload.h  
// Class Name OverloadClass
#ifndef _OverloadClass_H
#define _OverloadClass_H
#include < string >  
using namespace std ;
class OverloadClass
{
public:
    // Constructors and methods
private:
    x_;
    y_;
};
istream& operator>> (istream& in, OverloadClass &p);
#endif



// overload.cpp
#include < iostream >
#include < string >
#include < sstream >
#include < istream >  
extern "C"
{
#include "DUPoint.h"
}  
using namespace std ;  

void OverloadClass::input()
{
    char leftParen;
    char comma ;
    cin >> leftParen >> x_ >> comma;

    char rightParen;
    cin >> y_ >> rightParen;
}



// Constructor and method implementations  
istream& operator>> (istream& in, OverloadClass &p)
{ 
    p.input();
    return in;
}

The error I have been getting in Xcode is:

Link ./OverloadDirectory   
Undefined symbols: "operator>>(std:basic_istream >&, OverloadClass&)" referenced from: _main in overloadtester.o 
ld: symbol(s) not found collect2: ld returned 1 exit status

I dont have access to the computer with VS at this very moment hopefully when I do I can post the error I am getting from running the code on that IDE.

Edited in response to @Mark’s request for more details
Edited in response to @sbi’s request for more info on input()

Answer 1

The error undefined symbol is a linker error. It means that when you are linking all your code into a single executable / library, the linker is not able to find the definition of the function. The main two reasons for that are forgetting to include the compiled object in the library/executable or an error while defining the function (say that you declare void f( int & ); but you implement void f( const int & ) {}).

I don’t know your IDEs (I have never really understood Xcode) but you can try to compile from the command line: g++ -o exe input1.cpp input2.cpp input3.cpp ...