How to - forward declare a nested class or all within namespace?

How to - forward declare a nested class or all also within namespace, -
If there is inclusion of declared class to declared earlier in other file ? So - impossible to make a include?
Thanks.

(double side reference) ??
Like:

file1.h ----
#include "file2.h"
namespace 1_2
{

class 1
{
public:
host* member_host;
class 2{};
};

}

file2.h---

//impossible to include file1.h !!! -only forward declarations !
class host
{
class2* member; //Errors - 'class2 -undefined'
};

};#include "file2.h" #include "file2.h"

Since member is a class2 *, just forward declare class2.

Code:

---

//A.h
#include "B.h"
class A
{
B *b;
};

//B.h
class A;
class B
{
A *a;
};

---

this not works with type -inclusions
class - within class-within namespace.

In my sample how you can resolve that forward definition

class namespace 1_2::class1::class2;

generates "use of undefined class1" Error.??

That's because class1 isnt't in the global namespace, but in namespace 1_2 (wich, btw, isn't a legal identifier). You have to resolve the scope, by prefixing the declaration with the name of the namespace.

Code:

---

class host;
namespace N{
        class A
        {
        public:
                host *host_;
                class B{};
        };
}

class host{
        N::A::B *b_;
};

---

I had used full qualifying name, as changed in sample above,
but multiple type-inclusion not works,

than please,
can you chang you sample code to show how it must be right at
your opinion with all -namespace and nested class?

Code:

---

//file1.h
class host;
namespace N
{
        class A
        {
        public:
        host* host_;
        class B{};
        };
}

//file2.h
#include "file1.h"
class host
{
        N::A::B* member;
};

// ???.cpp file
#include "file2.h"
//.....

---

Sorry, - important -
file2 must be included to class 1, by conditions


at that forward declaration of?
of N::A::B
must be..

How it can be?

I don't see how that could work. Maybe you can rethink your design.