How to share variables/functions between classes from different files

[hajimeml]

I want to share variables/functions between classes. The classes are defined in different .h files. I read that the friend function allows us to do that but I keep getting error messages saying either that the class which holds the data to be shared is not defined or that the function being shared is not a member of the class. From the books and on the internet, the examples are written for classes defined within the same file. Is there a good example on how to do it when the classes are defined in different .h files?

[Peter_APIIT]

Show us the code and we can diagnose it together with you.

Does the variable/function located in a class which required by another class in different .h header file ?

I just you need to look for external linking.( if i not mistaken)

[hajimeml]

Show us the code and we can diagnose it together with you.

Does the variable/function located in a class which required by another class in different .h header file ?

I just you need to look for external linking.( if i not mistaken)

Thanks for the reply. As the program is too complex, I enclose the key parts only. Please note that the program was written in Borland C++ Builder 6.


In CStation.h
-----------------

class CStation: public Cbase
{
friend class CRemote; // to give class CRemote full access to CStation
private:
DoubleArray * data_to_be_shared; // DoubleArray is a class that stores an array of double.
// I want CRemote to be able to access data_to_be_shared.
};


In CStation.cpp
--------------------
I have a function to do some computations and stores the values into data_to_be_shared. I want CRemote to access this private data.


In CRemote.h
------------
class CStation; // forward declaration
class CRemote : public Cbase
{
// codes removed for clarify.
};


In CRemote.cpp
--------

void CRemote::ProcessData(void)
{
CStation station_class; // I got an error saying that CStation is an undefined structure.
// When I put #include "CStation.h" in CRemote.h and assigned it to
// data (see below), this error message disappeared but I got an
// error saying that station_class.data_to_be_shared cannot be
// accessed.
DoubleArray *data;

data = station_class.data_to_be_shared;
}

[VladimirF]

Did you also get an error:

error C2039: 'ProcessData' : is not a member of 'CRemote'

?

[Amleto]

in CStation.h do you forward dec. CRemote?

[hajimeml]

in CStation.h do you forward dec. CRemote?

No. Do you mean I have to put:

class CRemote;

at the beginning of CStation.h? I just tried and got four error messages (please note that the wordings are not exact as I translated from Japanese into English):

E2450 undeclared (undefined?) structure 'CStation'
E2449 station_class's size is unknown or zero
E2450 undefined structure 'CStation'
E2315 since there is no type declaration, data_to_be_shared is not a member of CStation.

[hajimeml]

Did you also get an error:

error C2039: 'ProcessData' : is not a member of 'CRemote'

?

No. I declared it under public in the class definition of CRemote (inside the .h file).

[VladimirF]

Could you create a small project with only those classes that demonstrate your problem and post it here?
Now we have to guess what is declared where and how...