Thread: Everything is Inherited?

  1. #1
    Registered User
    Join Date
    Jun 2007

    Everything is Inherited?

    I tried this :-

    using namespace std;
    class A
    	int x;
    class B:private A
    	int y;	
    		void foo()
    			cout<<x;		// error
    int main()
    	A a;
    	B b;
    	cout<<sizeof(a);		// 4
    	cout<<sizeof(b);		// 8;
    code suggests me, that even the private members of the base class are actually inherited and present in derived objects <sizeof>, but accessibility only restricts us to which members i can actually access from my derived object or infact in my derived class

    I would appreciated any confirmation

  2. #2
    Software Developer jverkoey's Avatar
    Join Date
    Feb 2003
    University of Waterloo
    That is true.

    Think of it this way: If variables from the base class weren't also kept around in derived classes, all functions from the base class that used those variables would now have nothing to work with.

  3. #3
    carry on JaWiB's Avatar
    Join Date
    Feb 2003
    Seattle, WA
    I'm not sure I understand what you're saying. 'x' is private in class A, so it can only be accessed by members of class A. If you declared it as protected (or public), then your code would compile.
    "Think not but that I know these things; or think
    I know them not: not therefore am I short
    Of knowing what I ought."
    -John Milton, Paradise Regained (1671)

    "Work hard and it might happen."

  4. #4
    Registered User
    Join Date
    Feb 2006
    I believe you misunderstand the purpose of access specifiers - Generally, they exist to control which parts of a class are internal implementation details (Or should be hidden away for whatever purpose), and which are the externally available components, by which other classes or other parts of the program may use the class.

    Inheritance causes the entire base class to be inherited - including members to which the derived class has no access. It is entirely down to the public/protected interface of the base class to allow control over base class components.

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