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soehrimnir

Forcing a method to be implemented by Subclass

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Hello, Suppose I have the following two classes:
  
// A superclass

class SuperClass
{
  public:
    void MethodToBeImplemented(void);
};

// A subclass

class SubClass : public SuperClass
{
  public:
    void MethodToBeImplemented(void);
}

void SubClass::MethodToBeImplemented(void)
{
  cout << "Blablabla";
}
  
Now, how can I force the SubClass to implement the specific method. By forcing I mean a compiler error would be generated if the method wasn''t implemented. Also, the SuperClass should not implement the method. If anyone knows Java, this is what I would like to get as a result, but then in C++:
  
abstract public class SuperClass {
  abstract public void MethodToBeImplemented(void);
}

public class SubClass extends SuperClass {
  public void MethodToBeImplemented(void) {
    System.out.print("Blablabla");
  }
}
  
I know there are abstract classes in C++ too, but I don''t know how they work. The abstract keyword doesn''t exist, so, any ideas?

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What you want is a pure virtual function, in your example:

    
// A superclass

class SuperClass
{
public:
virtual void MethodToBeImplemented() =0; // this line changed

};

// A subclass

class SubClass : public SuperClass
{
public:
void MethodToBeImplemented();
};

void SubClass::MethodToBeImplemented()
{
cout << "Blablabla";
}


The keyword virtual declares the function to be a virtual function (it can be redefined by child classes). And the =0 means that there is no definition of the funtion within the class hence the class is abstract as it contains at least one 'pure virtual function'.

[edit] Opps, fixed source error due to dodgy c&p. :D [/edit]

Edited by - meh on September 7, 2001 5:52:37 AM

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