Using WM_COPYDATA for interprocess communication (VFP9) -- Visual FoxPro : Using Win32 (WinAPI) Functions


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Using WM_COPYDATA for interprocess communication (VFP9)

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Before you begin:

An application sends the WM_COPYDATA message to pass data to another application running on the same PC.

The screen copy above shows a message sent from VFP to C# application. The MessageBox is invoked by C# form upon receiving the message.

See also:

Peer-to-peer LAN messenger built with Mailslot API functions

Using mailslots to send messages on the network

Using named pipes for interprocess communication

Using the NetMessageBufferSend to send messages on the network

How to create non-blocking Winsock server


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6380 bytes
Created: 2008-03-28 13:32:01
Modified: 2008-04-03 11:52:28
Visits in 7 days: 122

Listed functions:

CallWindowProc
GetWindowLong
GlobalAlloc
GlobalFree
GlobalSize
SendMessage

My comment:

The forms belonging to different VFP sessions (different processes) can exchange data in the same way. The window handle stays global through the Windows session.

The C# and VFP versions of this code sample are functionally identical. That allows exchanging data between .NET and VFP forms (applications).

In real life situation, prior to exchanging data the forms must have exchanged their window handles. That can be arranged by each form broadcasting a specific message that the other forms would recognize and respond. The FindWindow API is another option.

* * *
Comparing to other ways of interprocess communication (named pipes, mailslots, Winsock) the WM_COPYDATA has a certain edge: no need to implement any listening part. The OS does it for you.

* * *
http://blogs.msdn.com/oldnewthing/archive/2003/12/11/56043.aspx

if you need to pass more than 32767 characters of information to a child process, you`ll have to use something other than the command line.

* * *
Articles:

Interprocess Communications chapter on MSDN.

Foxpro Advisor Exchange Data Between Applications with Visual FoxPro 9 by Christof Wollenhaupt (recommended).

Word Index links for this example:

interprocess communication

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