How to share variables/functions between classes from different files

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?

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)

Quote:

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Originally Posted by 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)

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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;
}

Did you also get an error:

Code:

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

---

?

in CStation.h do you forward dec. CRemote?

Quote:

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Originally Posted by Amleto

in CStation.h do you forward dec. CRemote?

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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.

Quote:

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Originally Posted by VladimirF

Did you also get an error:

Code:

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

---

?

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

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...