What do you mean by 'Pure Virtual Function' in C++ \ VC++?

Current post is on what does 'Pure Virtual Function' mean?.

Lets examine:

What is pure virtual function ?

A pure virtual function is a virtual function which will force derived classes to override. If a class has any  pure virtual funtion(s), the class is called an "abstract class" and you can't create objects of that class.

Declaration Syntax:

return_value classname:: Func_Name( parameters ) = 0;

Example:

class AbstractBaseClass
{
     void ThisIsAPureVirtualFunction(void) = 0;
};

Why it is required?

- To specify an interface that must be provided by all classes deriving from it
- To make a class an abstract base class so that it cannot be instantiated

Can they have definition (method body)?

- Yes, they may have it.

1) If a class needs to be abstract & has no suitable candidate for virtual function, then my making destructor pure virtual & providing the definition, class is made virtual and derived class will have no issue in calling delete function

2) If a class need to provide a default behaviour but not let derived classes just inherit it "silently".


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