Functions and Objects
Friend Class in C++
A friend class can access all members (private or protected) of a class in which it is declared a friend.
Syntax
class originalClass {
friend class friendClass; //friendClass is a friend of originalClass
private:
dataType privateMember;
}
class friendClass {
public:
returnType someFunction(originalClass c){
c.privateMember = value; //private member of originalClass can be accessed
}
}
Notes
A friend class can access private and protected members of an object created from the originalClass, or an object of type originalClass passed in as a function parameter.
Example
//point on an x-y plane
class Point {
friend class Triangle;
private:
int x, y;
}
//triangle created from point plotted on x-y plane, using x, y, and the origin
class Triangle {
public:
int Base(Point p){
return p.x; //direct access to x, which is private member of p object
}
int Height(Point p){
return p.y;
}
double Area(Point p){
return p.x * p.y / 2;
}
}
