CODEWITHSUNDEEP
c++functionvirtual
AdityaG
AdityaG

Reputation: 438

Using Virtual functions in C++

I have a small problem using virtual functions in C++

I have a class B which extends class A.

Class A{
  virtual function 1 // does nothing 
  virtual function 2 // does nothing
}

class B : public class A {
  function 1 { does some thing }
  function 2 { does some thing }
}

I have another class implement

class implement {

  B b;
  A *a = &B;
  a.function 1();
  a.function 2();
}

This code when compiled gives the following error while compiling with GCC compiler

undefined reference to function 1 and function 2.

Please help me resolve this thanks in advance

Upvotes: 0

Views: 265

Answers (1)

Alok Save
Alok Save

Reputation: 206526

In C++ only pure virtual functions are allowed to exist without a function definition.
In your code you do not have any pure virtual functions. Pure virtual functions are the one's which have an =0 in the declaration.
For example: 

virtual void doSomething()=0;

The virtual member functions(function1() and function2()) in your base class A must have a definition since they are not pure virtual. You did not provide their definitions and hence the linker appropriately complains about missing definition.

undefined reference to function 1 and function 2

Upvotes: 5

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