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Using shared memory in Win32 applications

Posted on 1999-01-06
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Last Modified: 2010-04-02
I want to use simple windows messaging with a buffer of text
the allocation should be global yet there's a problem to use GlobalAlloc since it no longer shares memory between applications.
I also used CreateFileMapping but this solution is too dependent it won't solve my problem. any suggestions?
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Question by:arbitrary
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by:nietod
ID: 1181632
Try the WM_COPYDATA message.  It is the easiest way to pass data between applications.
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by:nietod
ID: 1181633
However, if you want to go with the file mapping, you should be able to.  I can see no reason why a file mapping won't work.  What do you mean by it is "too dependant"?  
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by:arbitrary
ID: 1181634
WM_COPYDATA needs a structure for data - COPYDATASTRUCT
it has 3 var in it - dwData cbData and lpData
I tried to assign the Data pointer (char* ) to the dwData and to
lpData , I know the value of the pointer is value yet there was
a memory violation as if it was null.
i tried to use file mapping but there's synchronization problems with it , which i can't base on synchronizing it since it will make my application less robust.
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LVL 22

Expert Comment

by:nietod
ID: 1181635
>> I tried to assign the Data pointer (char* ) to the dwData and to
>>  lpData , I know the value of the pointer is value yet there was
You must have done somethig wrong, can you post the code that sent the message and also the code that receives it?

>> which i can't base on synchronizing it
>> since it will make my application less robust.
synchronization will make your application more robust, not less.  What sort of problem were you having or you thought you were having?
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Expert Comment

by:jkr
ID: 1181636
What about a DLL that exports a shared memory section, e.g.

#pragma data_seg( ".shared")
// shared data goes here
char acSharedCharArray [ SHARED_ARRAY_SIZE] = "\0";
// initialization _is_ necessary
#pragma data_seg()

link using

SECTIONS
shared READ WRITE SHARED

in the .def file

Then, export 2 functions from this DLL that allow synchronized access to the data, e.g. 'BOOL SetData( char* pcData, long lnLen)' and 'long GetData( char* pcBuffer, long lnLen)'...
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by:stefanr
ID: 1181637
Another way of sharing data between applications besides WM_COPYDATA (easiest), memory mapped files (most powerful), and a shared DLL data segment is to use the network functions, like a named pipe, NetBios or TPC/IP.
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by:arbitrary
ID: 1181638
nietod method  is the most satisfiable,
i reckon you should get the points .

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nietod earned 100 total points
ID: 1181639
Then I'm answering again, but did you try it? Is it working?
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Expert Comment

by:nietod
ID: 1181640
So, what is happening, is this working?
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by:arbitrary
ID: 1181641
I've tried it and so far it works as good as it can get ,
I think it's good since the i don't need to synchronize between the proccesses .
As I said it's the most satisfying solution,
thanx.
oh sorry it took a long time i just completely forgot 'bout it.
so there you go
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