Question

I’m using VS2008 to build a plain old C++ program (not C++/CLI). I have an abstract base class and a non-abstract derived class, and building this:

Base* obj;
obj = new Derived();

fails with the error “‘Derived’: cannot instantiate abstract class”. (It may be worth noting, however, that if I hover over Base with the cursor, VS will pop up a tooltip saying “class Base abstract”, but hovering over Derived will only say “class Derived” (no “abstract”)).

The definitions of these classes are fairly large and I’d like to avoid manually checking if each method has been overridden. Can VS do this for me somehow? Any general tips on pinpointing the exact parts of the class’ definition that make it abstract?

Answer 1

The compiler should tell you in the error message. The following:

struct base
{
    virtual void foo(void) = 0;
    virtual void bar(void) = 0;
};

struct derived : base
{
    virtual void foo(void){}
};

int main(void)
{
    derived d;
}

Produces:

error C2259: ‘derived’ : cannot instantiate abstract class
due to following members:
‘void base::bar(void)’ : is abstract
see declaration of ‘base::bar’

It also does the same with dynamic allocation.