class Class2;
class Class1 : public BaseClass
.......
#include "class1.h"
#include "class2.h"
.....
#include "class3.h"
class Class2
.....
#include "class2.h"
......
#include "class1.h"
class Class2;
class Class3 : public Class1
.....
#include "class3.h"
#include "class2.h"