Please explain what this expression means

[Lilith]

This is something I can't seem to find in my books, which may be a bit
antiquated. Two examples:

virtual unsigned long size ()=0;

and

virtual void operator () ()=0;

I'm looking to find what purpose the "=0" serves.

 

[Neelesh Bodas]

I'm looking to find what purpose the "=0" serves.

"pure virtual function" - http://www.parashift.com/c++-faq-lite/abcs.html#faq-22.4

-N

 

[Lilith]

"pure virtual function" - http://www.parashift.com/c++-faq-lite/abcs.html#faq-22.4

Ah! Rather like an interface in that other language.

Thank you so much.