使用继承时，必须“#include”子类父类的头文件。 C ++

Question

I'm working on a multiple inheritance project in C++. I have separate files for class definitions (.h) and implementations (.cpp). Since this is the first time I've used inheritance in C++ (the rest of our assignments have been in C#) somethings are a little unclear.

Do I need to #include "parent.h" in child.cpp , or is it sufficient to have defined the inheritance relationship in child.h ie:

class child : parent 
{ 
     // child class definition
};

I was warned by an automated prompt that this might be a subjective question, so let me be explicit: I'm asking if this is a functional requirement for the inheritance to work properly, not if it's "good form" or anything along those lines.

Answer 1

Question

Do I need to #include "parent.h" in child.cpp , or is it sufficient to have defined the inheritance relationship in child.h

Answer

No, you don't need to #include "parent.h" in child.cpp . It is sufficient to #include "child.h" in child.cpp . The contents of "parent.h" are available in child.cpp since child.h already has #include "parent.h"

Answer 2

Just in case this isn't clear:
#include does a simple textual copy, there is no additional logic involved.

So no, it is not necessary. However the reason is not that you have defined the inheritance relation ship, but because #include "parent.h" in child.h already copies the text of parent.h into child.h and then #include child.h in child.cpp , copies the whole text (including the part from parent.h ) there. Another include would be redundant, and without the include guards it would even cause compiler errors.

Btw.:Conceptually, your compiler doesn't see the headerfiles as separate entities. It sees only a single textstream, which is produced by starting with the cpp file and then executing (recursively) all #include directives.