passing pointers between the process

[sachin871]

Hi,
I need to pass the character array or char* to the another process through BroadcastSystemMessage() API. If I use WPARAM for this, I get the junk address in the recieving process.I am doing something like this
Sender

..
char szTemp[32]={0};
strcpy(szTemp,"TEST");
ULONG uiMsg = RegisterWindowMessage(KP_EXPORT_STATUS_MSG);
		DWORD dwRecipients		= BSM_APPLICATIONS;
		DWORD dwFlags			= BSF_FORCEIFHUNG | BSF_POSTMESSAGE;
		
BroadcastSystemMessage(	BSF_FORCEIFHUNG|BSF_POSTMESSAGE,
						&dwRecepients,
						iServerFileFailure,
					(WPARAM)temp,
						0);
...

Reciever

ULONG uiMsg = RegisterWindowMessage(KP_EXPORT_STATUS_MSG);
		DWORD dwRecipients
LRESULT CALLBACK WndMainProc(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
{
	if(	message ==	uiMsg )
	{
		char* szTemp = (char*)wParam;
                                //szTemp is junk here
	}

Later I figured out that, pointers are meaningless between two processes as they will be having different process space. But it works if i send an interger as WPARAM instead of pointer.
I need to pass a string to another process. Is there any workaround for this problem??

Thanks

[Marc G]

Like you figured out yourself, you cannot send a pointer since it is only meaningful in 1 process.
Since it seems you are writing both applications, try to use WM_COPYDATA.
Make sure you read the remarks in that article!

[Arjay]

There are several forms of Interprocess Communication on Windows Platforms.

Another option is a Win32 dll with a share data segment. The dll provides a pair of GetSet methods and you put a string buffer into the shared seg area of the dll. You would have to load the dll in both processes.

One of the options mentioned in the link above is a memory mapped file. I use this technique in one of my articles in my subject line (Win32.. Part II). There is a Log Send and Log Receive sample that uses a MMF to send a structure containing a string buffer between two processes.

[VictorN]

As Arjay wrote there are many ways to send data between processes, and as Marc G pointed out using WM_COPYDATA is one of the simplest ones providing that both processes are on the same machine/desktop. But there could be also some problems with WM_COPYDATA if someone else (not your sender process) broadcasts it! See this essay:Using WM_COPYDATA

[sachin871]

Like you figured out yourself, you cannot send a pointer since it is only meaningful in 1 process.
Since it seems you are writing both applications, try to use WM_COPYDATA.
Make sure you read the remarks in that article!

Thanks a lot for the reply..
I gone through the link regarding WM_COPYDATA, But I dont have the handle for the window. That is why I am broadcasting the custom message. So I am afraid I cant use WM_COPYDATA.

However I am not getting why this works in the case of integers.

Thanks

[Marc G]

Because in the case of integers you send the real integer and not some pointer.

[sachin871]

Thanks Arjay and VictorN for reply..

Hello Mark G, I see that WPARAM is defined as UINT_PTR, so its a pointer. Doesnt it means that we are sending pointer and not the integer.

I am little confused abt it.

Thanks anyway.

[Marc G]

No, UINT_PTR is defined as follows:

#if defined(_WIN64)
 typedef unsigned __int64 UINT_PTR;
#else
 typedef unsigned int UINT_PTR;
#endif

So, it's a 32 bit uint when building 32 bit version and it's 64 bit when building 64 bit version. It is called _PTR because it could be used to store pointers since it will have the correct size.

[kirants]

But I dont have the handle for the window.

But, is it possible for you to get a handle to the window , say using FindWindow/Ex ?

If it is a string of known length, check to see if this post about atom tables is a viable option. http://www.codeguru.com/forum/showpo...7&postcount=14

[sachin871]

Thanks a lot for all ur replies..
Meanwhile I came across this tutorial on MSDN which is regarding the use of shared memory. I think its pretty easy and I can use that in future as well.

Here is the link