Question

The pure virtual destructor in base class should have a definition. Otherwise compiler will generate a call to base class destructor from the derived class destructor during link-time and will cause a link-error.

I tried to define the pure virtual destructor inside the base class like below:

class base
{
   public:
      base()
      {
         cout << "constructor in base class\n";
      }

      virtual ~base()=0
      {}
};

This gave the compilation error:

error: pure-specifier on function-definition

Then i tried to define the function outside the base class like below:

class base
{
   public:
      base()
      {
         cout << "constructor in base class\n";
      }

      virtual ~base()=0;
};

base::~base()
{

}

This removes the compilation error and it behaves as my understanding.

But my question is how does defining the pure virtual destructor outside the base class removes the compilation error?

Answer 1

Your second example is correct.

A lot of the other answers assume that it is illegal to have a pure virtual function with a default implementation, however that is incorrect.

In the case of a pure virtual destructor you must have a definition (see the link in xmoex answer).

It is true that:

§10.4/2 a function declaration cannot provide both a pure-specifier
and a definition

However, as you noticed it possible to provide a definition outside of the declaration.