Difference between Virtual function and Pure virtual function in C++

Virtual Function in C++
A virtual function a member function which is declared within a base class and is re-defined(Overriden) by a derived class. When you refer to a derived class object using a pointer or a reference to the base class, you can call a virtual function for that object and execute the derived class’s version of the function.

Pure Virtual Functions in C++
A pure virtual function (or abstract function) in C++ is a virtual function for which we don’t have an implementation, we only declare it. A pure virtual function is declared by assigning 0 in the declaration.

Similarities between virtual function and pure virtual function



  1. These are the concepts of Run-time polymorphism.
  2. Prototype i.e. Declaration of both the functions remains the same throughout the program.
  3. These functions can’t be global or static.

Difference between virtual function and pure virtual function in C++

Virtual function Pure virtual function
A virtual function is a member function of base class which can be redefined by derived class. A pure virtual function is a member function of base class whose only declaration is provided in base class and must defined in derived class.
Classes having virtual functions are not abstract. Base class containing pure virtual function becomes abstract.
Syntax:

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virtual<func_type><func_name>()
{
    // code
}

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Syntax:

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virtual<func_type><func_name>()
    = 0;

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Definition is given in base class. No definition is given in base class.
Base class having virtual function can be instantiated i.e. its object can be made. Base class having pure virtual function becomes abstract i.e. it cannot be instantiated.
If derived class do not redefine virtual function of base class, then it does not affect compilation. If derived class do not redefine virtual function of base class, then compilation error occurs.
All derived class may or maynot redefine virtual function of base class. All derived class must redefine pure virtual function of base class.


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