How can I make the base class unable to instantiate?

This is a discussion on How can I make the base class unable to instantiate? within the C++ Programming forums, part of the General Programming Boards category; For instance, classes A, B, and C derive from base class X. How can I make sure it's only A, ...

  1. #1
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    How can I make the base class unable to instantiate?

    For instance, classes A, B, and C derive from base class X. How can I make sure it's only A, B, and C that can instantiate, and not X? Thanks in advanced.

  2. #2
    C++ Witch laserlight's Avatar
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    Provide X with a pure virtual function, e.g. virtual ~X() = 0;
    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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    Confused Magos's Avatar
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    pure virtual methods:
    Code:
    class X
    {
      X();
      ~X();
    
      virtual void PureVirtualMethod() = 0;
    };
    Of course it must be implemented in a subclass.
    MagosX.com

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    Making all constructors of X or its destructor protected also effectively prevents instantiation (except within X's member functions or its friends). That ability to instantiate only in defined places can be useful at times.

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    That should do the trick. Thanks.

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