inheritance and polymorphism question of object of class A inhibiting class B and C

This is a discussion on inheritance and polymorphism question of object of class A inhibiting class B and C within the C++ Programming forums, part of the General Programming Boards category; I searched through the web and my textbook and I can only find examples of only for example class A ...

  1. #1
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    inheritance and polymorphism question of object of class A inhibiting class B and C

    I searched through the web and my textbook and I can only find examples of only for example class A inheriting characteristics of another class, less say class B. How hard would it be for class A to inherit characters of both class B and class C?

  2. #2
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    You can do that, it's called "Multiple inheritance", and as long as B and C aren't related, it's pretty much straight-forward.

    Code:
    class B { ... };
    class C { ... };
    
    class A: public B, public C
    { ... };
    --
    Mats
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    I'm getting a problem with Microsoft Visual C++ that I am experiencing an error message of
    (7) : error C2504: 'CSwitch' : base class undefined
    (8) : error C2504: 'CBulb' : base class undefined

    in the code:
    Code:
    class CLamp: public CSwitch, public CBulb
    {
    public:
    	CLamp(int x);				// constructor that will construct the lamp with x watts
    };
    Do I need to set the two base classes of CLamp as extern classes?

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    You need to include their header files.
    Quote Originally Posted by Bjarne Stroustrup (2000-10-14)
    I get maybe two dozen requests for help with some sort of programming or design problem every day. Most have more sense than to send me hundreds of lines of code. If they do, I ask them to find the smallest example that exhibits the problem and send me that. Mostly, they then find the error themselves. "Finding the smallest program that demonstrates the error" is a powerful debugging tool.
    Look up a C++ Reference and learn How To Ask Questions The Smart Way

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    I realized that I have included my header files in the wrong places. I have another problem: given my current CLamp declaration, how would I declare a new CLamp variable using my own constructor?

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    The normal way would be:
    Code:
    CLamp my_lamp(5);
    Of course you would name the variable something more meaningful and use a number other than 5, but that's how you do it.

    However, you are not using inheritance correctly. A lamp has a switch and a bulb. Public inheritance of for when something works like something else. When an object is made of another object, you use containment:
    Code:
    class CLamp
    {
        CSwitch switch;
        CBulb bulb;
    public:
        CLamp(int watts);
    
        // ...
    };

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    can you please show us your whole code? or atleast what matters..

    headers, base class, derived classes, classes in action etc

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    Officially An Architect brewbuck's Avatar
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    Quote Originally Posted by stanlvw View Post
    I'm getting a problem with Microsoft Visual C++ that I am experiencing an error message of
    (7) : error C2504: 'CSwitch' : base class undefined
    (8) : error C2504: 'CBulb' : base class undefined

    in the code:
    Code:
    class CLamp: public CSwitch, public CBulb
    {
    public:
    	CLamp(int x);				// constructor that will construct the lamp with x watts
    };
    This is an awful example. A lamp is not a switch, nor is it a bulb. It is an object which CONTAINS a switch and a bulb. Inheritance is not what you want here. What you want is composition:

    Code:
    class CLamp
    {
    private:
        CSwitch switch;
        CBulb bulb;
    };
    My house contains a dog. That doesn't mean my house is a dog.

  9. #9
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    I got the problem related to this thread figured out now. Thanks for your help.

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