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Multiple instances of ActiveX OCX share glabal variables by default; how do i make each instance unique

joevm3
joevm3 asked
on
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Last Modified: 2008-02-01
i have an OCX written in MS C++ 6 that i am using in VB6
it works fine but when i load multiple instances of the OCX, say 2 on a vb form the global variables are shared between the two of them. here is an example:

in the ControlNameCtl.cpp file if i have:

int hello=0;

int SomeFunction(short param1)
{
hello++;
return hello;
}

----------
now if i load two OCX's and i call SomeFunction on the first,it will return 1 [expected]
and then if i call SomeFunction on the second OCX it will return 2 [unwanted]

i tried using the static keyword but i had no luck with that.

Thank you for your help,
Joe
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Commented:
I don't beleive that this happens, possibly there is something else in the code. In any case, make hello variable member of the control class, this should help.
Commented:
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Commented:
AlexFM is right.

To share variables across instances you need to specify Data segment as shared.
// Global and static member variables that are not shared.

#pragma data_seg("SHARED")  // Begin the shared data segment.
// Integers, char[] arrays and pointers. These variables declared here are shared
#pragma data_seg() // End the shared data segment and default back to
                              // the normal data segment behavior.

//This tells the linker to generate the shared data segment.  
#pragma comment(linker, "/section:SHARED,RWS")

I think your code pasted here is incomplete or your are missing something.

Author

Commented:
I tried #pragma data_seg() before the declaritions.
It did not work.

AlexFM, how do i make the variable 'hello' a member of the control class?


btw the code is just an example as the actual code is quite large, i don't think there is anything in the code affecting the default compiler settings.

Thank you,
Joe

Author

Commented:
Okay it almost works like this:
if i use the ide to make a member variable [public] it works (the variables are not shared) but i can only access the variable within that class (CActivePhotonCtrl)
i tried using  extern int hello;  but that failed an i also tried  CActivePhotonCtrl::hello++;  but that also failed with the error "error C2597: illegal reference to data member 'CActivePhotonCtrl::hello' in a static member function"

how may i access a public member variable belonging to CActivePhotonCtrl from another class?

Thank you,
Joe

Commented:
Using pointer to this class. This is not specific to COM, just C++.

class A
{
    public:
       int x;
};

from any plase having A* pA pointer:
pA->x = 1;

Static class member will be also shared between all control instances, you need non-static member.
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