THINK++ — Engineering Visualized

Special Access

Friend Functions

A function that is NOT a member of a class but has permission to access the class's private and protected members.

DECLARATION

class Box {
    int width;
public:
    friend void printWidth(Box b); // Friend!
};

NOT A MEMBER

It's defined outside the class scope and doesn't have a this pointer.

ONE-WAY

Friendship is granted, not taken. The class must explicitly declare its "friends".

Common Use Case: Operator Overloading

Friend functions are frequently used for overloading the insertion << and extraction >> operators for custom classes.

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