Calling a protected method for a member object in C++

Question

If i have two classes, for example like this

class A {
    ...
    protected:
        B* test;
        aFunction();
};

class B {
    ...
    protected:
        A* test1;

    public:
        bFunction();
};

can I do this inside bFunction() of class B:

bFunction(){
    test1->aFunction();
}

Basically, can I call a protected function of a certain class from the class that's not derived from that function?

Only one answer to that: No. – Some programmer dude Sep 29 '13 at 17:02 — Some programmer dude, Sep 29 '13 at 17:02

score 4 · Accepted Answer · answered Sep 29 '13 at 17:12

4

The "point" of the protected is that only classes that are derived from the baseclass can call those functions.

If you have a good reason to do this, then make the class a friend, e.g. add friend class B; inside class A.

answered Sep 29 '13 at 17:12

Mats Petersson

126,704
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score 2 · Answer 2 · answered Sep 29 '13 at 17:35

2

It is recommended to avoid such inevident mutual dependencies. A necessity to use friend functions often indicates bad architecture.

answered Sep 29 '13 at 17:35

borx

411
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7

villekulla · Answer 3 · 2013-09-29T17:27:56.373

From cplusplus.com:

Private and protected members of a class cannot be accessed from outside the same class in which they are declared. However, this rules does not affect friends.

You can call protected and privat methods from other classes, when those are 'friends':

In your case that would be:

Class A {
    ...
    protected:
        B* test;
        aFunction();
    friend class B;
}

Often that is considered bad practice, but for tightly coupled classes that is ok.

Calling a protected method for a member object in C++

3 Answers3