C ++ private inherited access

 

Environment: VS2010

Question: Exploring access to C ++ private inheritance from the outside

Code:

 

# Include <iostream>

 

Using namespace std;

Class

{

Public:

A (){

A = 0;

Cout <"A: A ()" <endl;

}

Int;

};

Class B: protected

{

Public:

B (){

I = 1;

Cout <"B: B ()" <endl;

}

 

Public:

Int I;

};

Int main (void ){

 

B b2;

B2. I = 20;

A * pp = & b2;

Cout <"pp-> a:" <pp-> a <"" <"b2. I" <b2. I <endl;

Return 0;

}

 

A * pp = & b2; error: // error C2243: "type conversion": conversion from "B *" to "A *" exists, but cannot be accessed

That is, the pointer to the base class can be converted to a derived class, but it cannot be accessed because it is a protected inheritance.

Change A * pp = & b2; To A * pp = (A *) & b2; that is, convert the pointer pointing to the derived class to A base class pointer for access.

The effect is as follows:

 

Add the following code to Class B:

 

Void SetB (int n ){

This-> a = n;

}

 

In this way, you can also modify a of the base class.

 

Although it can be accessed, it is not recommended to forcibly convert the pointer pointing to a derived class to a base class pointer because it violates the principle of protection inheritance.

Note: The forced conversion of C ++ is very powerful, and it does not check the type.

 

Author Wentasy