Programming Forums - accessibilty class

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accessibilty class

Hello,
I need to understand the accessibility of inheritance.
I have this code:

#include<iostream>

using namespace std;



class X {

       protected:

                    void fn() { cout << "In X::fn()\n"; } 

       public:

                    X() { cout << "In X::X()\n"; } 

                   virtual void print() { cout << "In X::print()\n"; fn(); } 

                   virtual void fnx() { cout << "In X::fnx()\n"; }

};



class Y : protected X { // Inheritance of Y from X

        public:

                Y() { cout << "In Y::Y()\n"; } 

                virtual void print() { cout << "In Y::print()\n"; fn(); } 

                virtual void fny() { cout << "In Y::fny()\n"; }

};



class Z : public Y { // Inheritance of Z from Y

        public:

                 Z() { cout << "In Z::Z()\n"; } 

                 virtual void print() { cout << "In Z::print()\n"; fn(); } 

};



void foo1(X& obj) { obj.print(); } 

void foo2(Y& obj) { obj.print(); } 

void foo3(Z& obj) { obj.print(); } 

void foo4(X obj) { obj.print(); } 

 

int main() {

       X objx; 

       Y objy; 

       Z objz; 

       foo1(objx); 

       foo4(objx); 

       foo2(objy); 

       foo4(objy); // `X' is an inaccessible base of `Y' 

       foo3(objz); 

       foo4(objz); X' is an inaccessible base of `Z' 



return 0;}

The error is in red on the code.
I want to understand what is happening at those errors points.
I read the documentation of accessibility rules but I am wondering why we dont have an error for

foo3(objz)

or the other since they all calling X::fn()
can someone help me please?

thank you
B

Read the definitions of "public", "private", and "protected".

OK relatively to protected inheritance, I quote:
"
- inherited public and protected members become protected members of the derived class.

- all the inherited members are inaccessible to the rest of the program (main & other non-memberfunctions)

- each subsequently derived class has access to the combined set of the protected and public members of the previous base classes.(this is where I get confused in respect to the code I have.)"

why foo4(objy) would not compile?

When it calls print(),print() calls fn() since all subsequent derived class have access to the previous base class!!

Quote:

Originally Posted by brad sue (Post 121047)

why foo4(objy) would not compile?

Because it is being called from main(), and main() has no access to non-public attributes, base classes, or member functions of class Y.