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I was reading up on pure virtual functions in C++ Primer Plus 5th edition and I'm still a little unclear as to what their purpose is. From my understanding, they are used in abstract base classes so that an object cannot directly be created from the class but rather other classes must derive from it. In this case, any function declared as pure virtual using "=0" MUST be defined within the derived classes.

Is this essentially what pure virtual functions are ALL about?