What does this code mean?

This is a discussion on What does this code mean? within the C++ Programming forums, part of the General Programming Boards category; Code: virtual bool isCorrectAnswer(const std::string& answer) const = 0; Im guessing that it is a overide-able yes or no which ...

  1. #1
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    What does this code mean?

    Code:
     virtual bool isCorrectAnswer(const std::string& answer) const = 0;
    Im guessing that it is a overide-able yes or no which is decided later.

    It checks if the value stored in answer is correct?

    Probably not correct just wondering if anyone could explain

    would this be considered a virtual function or constructor, im guessing function but then again it is assigned value of 0

    (And yes I know the snippet is short)

  2. #2
    Cat without Hat CornedBee's Avatar
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    The =0 makes the function pure, i.e. the containing class is abstract, as is any derived class unless it has an overriding definition of this function.

    As for the semantics, you can only guess - the name and signature suggest that the function indeed checks the value of answer and returns whether it is correct, but that depends on the implementation. Of course, if this function does anything else, it's grossly misnamed.
    All the buzzt!
    CornedBee

    "There is not now, nor has there ever been, nor will there ever be, any programming language in which it is the least bit difficult to write bad code."
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  3. #3
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    Do a search for "pure virtual function" and you'll find your answer.
    "I am probably the laziest programmer on the planet, a fact with which anyone who has ever seen my code will agree." - esbo, 11/15/2008

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    Code:
    virtual bool isCorrectAnswer(const std::string& answer) const = 0;
    This is a pure virtual function..means if it is declared in a class ,the class becomes an abstract class that means you can't create any object of that class and it will enforce any subsequent classes those are derived from it to implement this function in their own class...

  5. #5
    Cat without Hat CornedBee's Avatar
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    it will enforce any subsequent classes those are derived from it to implement this function in their own class...
    No, it won't. I worded my post very precisely.
    A class must define or inherit a concrete implementation of all its pure functions in order not to be abstract. However, if a class doesn't mind being abstract, it doesn't need to override its pure functions. There is a school of thought in object-oriented design (especially in C++) that says that only leaf classes of the hierarchy should ever be concrete.
    All the buzzt!
    CornedBee

    "There is not now, nor has there ever been, nor will there ever be, any programming language in which it is the least bit difficult to write bad code."
    - Flon's Law

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