How to use a class_b created into class_a. Both classes lies into a custom DLL?

I have a little muddle with the use of a class inside another class, and mixed with the dll perspective. (Althought I dont think this were the problem)

I have a DLL built successfully: MYCLASS_A.

I have a project, i want to use myclass.dll
I create an instance of it at my main.cpp.
Then, I use it using 'extern' .
All warks fine, I can use it in other cpp files.
But...
I want to have a MYCLASS_B (also into the dll) instantiated into MYCLASS_A, I want simply to write :
MYCLASS_A.MYCLASS_B.Myfunction.

I dont know how to write and use it...
The code :

myclass_a.h

Code:

---

#ifndef MYCLASS_A_H
#define MYCLASS_A_H
#include "myclass_a_global.h"
#include "myclass_b.h"
 
class MYCLASSASHARED_EXPORT Myclass_a
{
public:
    Myclass_a();
    Myclass_b myclass_b1;
};
 
#endif

---

myclass_a.cpp

Code:

---

#include "myclass_a.h"
 
Myclass_a::Myclass_a()
{
 
}
 
Myclass_b myclass_b1;

---

When compile the project that use the DLL I have and 'undefined reference' to
myclass_a.myclass_b1.mymethod.
So, I suspect that the myclass_b1 is not really created ?
Please help....

Did you export Myclass_b as you did Myclass_a?

Code:

---

class MYCLASSASHARED_EXPORT Myclass_b
 
{
public:
 
Myclass_b();
...
 
};

---