There are 2 classes, A and B:

----------
FileA.h
----------
#include <FileB.h>
class B; //Why forward declaration here
class A{
...
B objB;
...
};
----------
FileA.cc
----------
#include <FileA.h>
...implementation of class A...

----------
FileB.h
----------
class A; // I understand this is forward declaration
class B{
...
A objA;
...
};

----------
FileB.cc
----------
...Implementation of class B

What I don't understand is that why forward declare class B in FileA.h?
Seems FileA.h already included FileB.h.