Inheritance

This is a discussion on Inheritance within the C++ Programming forums, part of the General Programming Boards category; What i wan to do is make a base class from which you can derive your own class. I want ...

  1. #1
    Registered User mrafcho001's Avatar
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    Inheritance

    What i wan to do is make a base class from which you can derive your own class.

    I want the user to be able to override the functions in the base class. But if they don't override them i want it to use the functions from the base class.

    I've tried to make the functions in the base class virutal, but that forces the user deriving the class to override the functions.

    I want to leave it up to the user weather to override the functions or not. If not use the ones from the base class.
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  2. #2
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    >> I've tried to make the functions in the base class virutal, but that forces the user deriving the class to override the functions.

    This is not true. You want to make the functions virtual and provide an implementation. Only when the function is pure virtual (meaning it has = 0) does it force the derived classes to override it.

  3. #3
    Tropical Coder Darryl's Avatar
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    making the base class functions virtual does not force the derive classes to overide them, making them pure virtual does
    Code:
    virtual void doSomthing() // virtual
    {
         // do something
    }
    
    virtual void doSomethingElse() = 0; //pure virutal
    Last edited by Darryl; 03-02-2006 at 02:46 PM. Reason: smartass :-)

  4. #4
    Devil's Advocate SlyMaelstrom's Avatar
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    C++ accepts two word identifiers now?

    tee hee
    Last edited by SlyMaelstrom; 03-02-2006 at 12:12 PM.
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  5. #5
    Registered User mrafcho001's Avatar
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    thanks, i guess i must of been doing something wrong earlier, works fine now.

    But what if i want the derived class to access private members from the base class?

    i have something like this

    Code:
    class Base
    {
    private:
    int a1;
    public:
    virtual void func1();
    };
    
    class Derived: public Base
    {
    public:
    void func1()
    {
    cout << a1 << endl;
    }
    };
    Code:
    Error	1	error C2248: 'Base::a1' : cannot access private member declared in class 'Base' line 18
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  6. #6
    Devil's Advocate SlyMaelstrom's Avatar
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    Make it protected? Don't know if that's an option for what you're doing.
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  7. #7
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    You cannot access private members of the base class because they are private. Make protected accessor methods in the base class. You could make the variable protected, but that is not really good design.

  8. #8
    Registered User mrafcho001's Avatar
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    Works perfectly.

    Thanks guys.
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  9. #9
    Tropical Coder Darryl's Avatar
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    Quote Originally Posted by SlyMaelstrom
    C++ accepts two word identifiers now?

    tee hee
    sorry, was working with my c++ beta copy

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