How virtual functions can be implemented in C++?

 

 

Posted Date: 3/15/2013 6:31:11 AM | Location : United States

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A: Virtual functions are implemented by a table of function pointers, called vtable. There is one entry in table per virtual function in class. This table is formed through the constructor of the class. While a derived class is constructed, its base class is constructed _rst that creates the vtable. If the derived class overrides any of base classes virtual functions, those entries into the vtable are overwritten through the derived class constructor. It is why you must never call virtual functions from a constructor: since the vtable entries for the object might not have been set up through the derived class constructor still, so you might end up calling base class implementations of those virtual functions Posted by | Posted Date: 3/15/2013 6:31:40 AM

A: Virtual functions are implemented by a table of function pointers, called vtable. There is one entry in table per virtual function in class. This table is formed through the constructor of the class. While a derived class is constructed, its base class is constructed _rst that creates the vtable. If the derived class overrides any of base classes virtual functions, those entries into the vtable are overwritten through the derived class constructor. It is why you must never call virtual functions from a constructor: since the vtable entries for the object might not have been set up through the derived class constructor still, so you might end up calling base class implementations of those virtual functions Posted by | Posted Date: 3/15/2013 6:32:48 AM

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