When to forward reference and when to include?

Headers and Includes: Why and How says -

Quote:

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If, for example, class A uses class B, then class B is one of class A's dependencies. Whether it can be forward declared or needs to be included depends on how B is used within A:

- do nothing if: A makes no references at all to B
- do nothing if: The only reference to B is in a friend declaration
- forward declare B if: A contains a B pointer or reference: B* myb;
- forward declare B if: one or more functions has a B object/pointer/reference
as a parementer, or as a return type: B MyFunction(B myb);
- #include "b.h" if: B is a parent class of A
- #include "b.h" if: A contains a B object: B myb;

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Is it as simple as that or is there something more to it?

After you replace "class" with "struct", it's even simpler because friendship, references, and parents don't exist in C, and you don't have to worry about the case where a member function that is defined inline in a class definition directly instantiates an object because member functions don't exist in C either.

:+1: Thank you very much.