Why doen't my code work? c++ operator [duplicate] - c++

Question

This question already has answers here:
What are the basic rules and idioms for operator overloading?
(8 answers)
Closed 6 years ago.
//main()
#include <iostream>
#include "Circle.h"
#define PI 3.1415965 //defining the pi number
using namespace std; //I want to create a class that has the characteristics of a circle
int main()
{
Circle c1(1); //making a class object
cout<<c1; //using the operator<< after overloading it
return 0;
}
//circle.h
#include <iostream> //I'm just practicing with these things so my code will probably have some mistakes but I really cannot understand where is the right place for the operator<< because I receive errors all the time
using namespace std;
class Circle //creating the class circle
{
public:
Circle(); //constructor with zero members
Circle(float r); //constructor with one member
float getPerimetre(); //getting the perimeter of the circle
float getArea(); //getting the area of the circle
friend ostream &operator<<(ostream &mystream, Circle &p); //making the operator<<
private:
float radius; //private members
};
#endif // CIRCLE_H
//circle.cpp
#include "Circle.h"
#include <iostream>
#define PI 3.14159265 //defining the pi number
using namespace std;
Circle::Circle() //creating the constructor with zero members
{
radius=0;
Circle::Circle(float r) //creating the constructor with one member
{
radius=r;
}
float Circle::getPerimetre() //explaining the functions get perimetre
{
return (2*PI*radius);
}
float Circle::getArea() //and get area
{
return (PI*radius*radius);
}
ostream &operator<<(ostream &mystream, Circle &p) //i'm not sure if this is the right place to write this
{
mystream<<radius<<", "<<getPerimetre()<<", "<<getArea()<<endl;
return mystream;
}
out from all the things that I've read I really cannot understand where is the correct spot to write this operator and why I keep receiving errors when I run the project. I am new to this and also to this site so any help would be very apreciated

Answer 1

Your operator<< is at good place, however since it isn't member function you can't access members without object:
p.radius instead of radius
p.getPerimetre() instead of getPerimetre()
p.getArea() instead of getArea()
ostream &operator<<(ostream &mystream, Circle &p) //i'm not sure if this is the right place to write this
{
mystream<<radius<<", "<<p.getPerimetre()<<", "<<p.getArea()<<endl;
return mystream;
}

Answer 2

friend ostream &operator<<(ostream &mystream, Circle &p);
should be
friend ostream &operator<<(ostream &mystream, const Circle &p);
and the implementation should look like
ostream &operator<<(ostream &mystream, const Circle &p)
{
mystream<<p.radius<<", "<<p.getPerimetre()<<", "<<p.getArea()<<endl;
return mystream;
}
this also requires that you classify getPerimetre() and getArea() as const functions in your class declaration
class Circle {
public:
// ...
float getPerimetre() const;
// ^^^^^
float getArea() const;
// ^^^^^
// ...
};
and definition
float Circle::getPerimetre() const {
// ^^^^^
return (2*PI*radius);
}
float Circle::getArea() const {
// ^^^^^
return (PI*radius*radius);
}