c++ multiple definitions of operator<<

Question

I am attempting to override the << operator for a class. The purpose is basically to implement a toString() like behavior for my class, so t

Answer 1

You're breaking the one definition rule. A quick-fix is:

inline ostream& operator<<(ostream& out, const CRectangle& r){
    return out << "Rectangle: " << r.x << ", " << r.y;
}

Others are:

• declaring the operator in the header file and moving the implementation to Rectangle.cpp file.
• define the operator inside the class definition.

.

class CRectangle {
    private:
        int x, y;
    public:
        void set_values (int,int);
        int area ();
        friend ostream& operator<<(ostream& out, const CRectangle& r){
          return out << "Rectangle: " << r.x << ", " << r.y;
        }
};

Bonus:

• use include guards
• remove the using namespace std; from the header.

Answer 2

You are putting the definition of a function in a .h file, which means that it will appear in every translation unit, violating the One Definition Rule (=> you defined operator<< in every object module, so the linker doesn't know which is "the right one").

You can either:

• write just the declaration of your operator (i.e. its prototype) in the .h file and move its definition to rectangle.cpp
• make operator<< inline - inline functions are allowed to be defined more than once, as long as all the definitions are identical.

(Also, you should use header guards in your includes.)