"cout <<" error

ok im trying to fix the code of three classes and i've managed to fix every error but 4. all 4 errors are the same just in different spots of 2 functions in a class. the errors are

Code:

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D:\classesexamples\geometry\Box.cpp(49) : error C2679: binary '<<' : no operator defined which takes a right-hand operand of type 'class Point' (or there is no acceptable conversion)

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and the source code that it points to is

Code:

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void Box::getCorners(Point& a, Point& b) {
    corner1 = a;
    corner2 = b;
    cout << corner1 << endl;
    cout << corner2 << endl;
}

void Box::print() {
    cout << corner1 << endl;
    cout << corner2 << endl;
}

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i just dont get why it says there is and error with <<

cout doesn´t know how it should display Point. Try overload operator << for class Point (I assume that corner1 and corner2 are instances of class Point).

could you explain what you mean by the overload operator <<

and the values corner1 and corner2 are supposed to represent x and y values that are private members in the class Point.

Hi. For one of the projects in my CS class this semester we had to overload the >> and << operators for a complex # class. The reason we had to do that was because the class complex creates a new data type, Complex. so when u did the following

Code:

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Complex a;
cout << a;

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you would get the same error

Quote:

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D:\classesexamples\geometry\Box.cpp(49) : error C2679: binary '<<' : no operator defined which takes a right-hand operand of type 'class Point' (or there is no acceptable conversion)

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- cout doesnt know how to display the data type Complex. Your problem is that cout doesn't know how to display the Point data type, so you have to tell it how by overloading the << operator.

To do that you have to make the << operator a friend of the class like this

Code:

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class Point{
  public:
    friend ostream& operator<< (ostream& os, Point& x);
    // whatever else
};

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after that u have to tell the << operator what to output like this

Code:

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ostream& operator<< (ostream& os, Point& x)
{
os << x; // make this whatever you want to output
return os;
}

---

Hopefully all thats right :D (someone more experienced correct if not). Hope that helps.

<< should have a constant second parameter:
friend ostream& operator<< (ostream& os, const Point& x);

Oops. :eek: Forgot that. Thanks for the correction.

thx for the reply but i got a few questions seeing im not all that good or experienced at c++ especially classes

what does friend mean or represent and can i be called anything and why is it there?

and after all that to use it i just use "<<" nothing else or is it "operator<<" that i use

The friend keyword allows the so-marked class or function to access all member of the class that contains the friend-declaration, even the protected and private members.

so when i got all that how do i use the << operator? the same way?

Yes.

Overloading operators is basically just defining a new function. Except, you can't just put the operator itself, since that would be... an operator. So you use the 'operator' keyword before the operator itself, and then the operator, then the argument list, etc.

That's why it's 'operator <<' instead of just '<<' when you define it.