Question

I have a class called A, which has its .cpp and .hpp files. It depends on classes B and C. Now, I’m wondering, should I #include B.hpp and #include C.hpp in A.cpp or A.hpp? I think it would be beneficial for me to #include in the A.hpp file, because I’m creating a vector of B*‘s, and I’m not sure that the compiler will know the correct size of B if I only forward declare it (so I couldn’t pointer increment correctly)… By “forward declaration”, I mean writing class B; and class C; in the beggining of A.hpp.

Answer 1

As already mentioned, you can often work-around having to #include stuff by using forward declarations, and indeed the best practice is to minimize the amount of other headers included.

But: To answer your questions headline: yes you may, and the common mechanism to avoid “circular inclusion” is the following

A.hpp:

#ifndef A_HPP_INCLUDED
#define A_HPP_INCLUDED

... // code

#endif

Now if say B.hpp includes A.hpp, and subsequently, C.hpp looks like:

#ifndef C_HPP_INCLUDED
#define C_HPP_INCLUDED

#include "A.hpp"
#include "B.hpp"

...
#endif

Then you won’t get an error stating that e.g. ‘class A’ has already been defined.