Question

If we define two C++ classes. One is:

abstract class A {
  public:
    enum E {F, G, H;}
};

Another is class B, and how I can use the enum E in class A then? Assuming both B and A are in the same namespace. I know in C# we can use something like:

A.E

directly, but seems that is not the case of C++.

Answer 1

In C++, . and -> are for accessing a member of this particular instance of an A object. :: is for accessing things in the scope of class A. This includes statics, enums, and function pointers.

So in C++ you want A::F or A::G if you want enum value.

for the enum type you do A::E

class A
{
public:
    enum E { F , G , H};
    virtual ~A() = 0; //a pure virtual function to make the class abstract
};

int main()
{
    A::E x; // x is declared as the enum
    x = A::F; // x is assigned a particular enum value

    return 0;
}

Also to make the class abstract you provide a pure virtual function.