Difference between a virtual function and a pure virtual function

Question

What is the difference between a pure virtual function and a virtual function    I know  Pure Virtual Function is a Virtual function with no body   but what does this mean and what is actually done by the line below   virtual void virtualfunctioname     0

User · Answer

You can actually provide implementations of pure virtual functions in C     The only difference is all pure virtual functions must be implemented by derived classes before the class can be instantiated

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For a virtual function you need to provide implementation in the base class  However derived class can override this implementation with its own implementation  Normally   for pure virtual functions implementation is not provided  You can make a function pure virtual with  0 at the end of function declaration  Also  a class containing a pure virtual function is abstract i e  you can not create a object of this class

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A pure virtual function is usually not  but can be  implemented in a base class and must be implemented in a leaf subclass   You denote that fact by appending the    0  to the declaration  like this   class AbstractBase       virtual void PureVirtualFunction     0      Then you cannot declare and instantiate a subclass without it implementing the pure virtual function   class Derived   public AbstractBase       virtual void PureVirtualFunction   override         By adding the override keyword  the compiler will ensure that there is a base class virtual function with the same signature

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A virtual function makes its class a polymorphic base class  Derived classes can override virtual functions  Virtual functions called through base class pointers references will be resolved at run-time  That is  the dynamic type of the object is used instead of its static type     Derived d   Base amp  rb   d      if Base  f   is virtual and Derived overrides it  Derived  f   will be called  rb f        A pure virtual function is a virtual function whose declaration ends in  0   class Base              virtual void f     0             A pure virtual function implicitly makes the class it is defined for abstract  unlike in Java where you have a keyword to explicitly declare the class abstract   Abstract classes cannot be instantiated  Derived classes need to override implement all inherited pure virtual functions  If they do not  they too will become abstract   An interesting  feature  of C   is that a class can define a pure virtual function that has an implementation    What that s good for is debatable      Note that C  11 brought a new use for the delete and default keywords which looks similar to the syntax of pure virtual functions   my class my class const  amp     delete  my class amp  operator  const my class amp     default    See this question and this one for more info on this use of delete and default

[c++] Difference between a virtual function and a pure virtual function

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