TechnologY

Pure virtual functions

http://www.learncpp.com/cpp-tutorial/126-pure-virtual-functions-abstract-base-classes-and-interface-classes/

Pure virtual (abstract) functions and abstract base classes

So far, all of the virtual functions we have written have a body (a definition). However, C++ allows you to create a special kind of virtual function called a pure virtual function (or abstract function) that has no body at all! A pure virtual function simply acts as a placeholder that is meant to be redefined by derived classes.

To create a pure virtual function, rather than define a body for the function, we simply assign the function the value 0.

class Base

{
public:
    const char* SayHi() { return "Hi"; } // a normal non-virtual function   
    virtual const char* GetName() { return "Base"; } // a normal virtual function
    virtual int GetValue() = 0; // a pure virtual function
};
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