CODEWITHSUNDEEP
c++dllpragma
Myn
Myn

Reputation: 691

Sharing an object between instances of a C++ DLL

Good morning all,

Forgive me if the title is not too clear, I'll try to explain more here:

I am currently working with the ASI for VBS2. VBS2 executes functions from a VBS2 DLL plugin. I have my own application which I want to use to modify variables within that plugin whilst it is being used, to change what is being executed by VBS2. I began by, foolish as it may be, directly changing the variables with my application whilst the VBS2 program was running.

When this did not work I tested and found that the VBS2 program was using a different instance of the "message" object, in which I was storing the variable, to the one being accessed by my application.

What I would like to do is have my application access the same instance of the object being accessed by VBS2. I have experimented a bit with 

#pragma data_seg(".testseg")
Message msg;
void foo(...); //etc.
#pragma data_seg()

but for some reason or another it still appears there are two instances being used.

I would greatly appreciate any and all help, and would add that C++ is a new language to me so please be gentle. :)

Thanks, M

Upvotes: 1

Views: 851

Answers (2)

jcoder
jcoder

Reputation: 30035

You need to use linker flags to tell the linker to place that segment in sharable memory.

See http://msdn.microsoft.com/en-us/library/ms933104.aspx

I belive you need to add something like

#pragma comment(linker, "/SECTION:.testseg,RWS")

to your program. I'm not sure, this may only work in a DLL...

Upvotes: 1

Eugene Smith
Eugene Smith

Reputation: 9378

If I understand correctly what you want, you can't do this with standard C/C++ tools. Your program and the other program live in separate memory spaces and they are completely insulated from each other. If your program has administrative privileges, you can attempt to read & write the memory space of the other process using WriteProcessMemory():

http://msdn.microsoft.com/en-us/library/ms681674%28v=VS.85%29.aspx

But then there's a problem of finding the right object in that memory space.

It's not clear whether you have the source for the plugin. If you do, there are other interprocess communication techniques that can be utilised. None as simple as just changing the variable, unfortunately.

Upvotes: 0

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