Question

What is the best and easiest way to send a string from one instance of my program to another instance of my program? The receiving program has to execute a procedure, using the received string as a parameter.

I started reading about DDE but I got confused. What other options do I have, and what is the easiest way to implement this?

Answer 1

Use named Pipes, but I would recommend Russell Libby’s named Pipe components. There is a TPipeClient and TPipeServer component.

As of (2013-10-04) Francoise Piette and [e-mail] updated this source code to compile with Delphi 7 to XE5 (earlier versions may compile however untested) and put it here: http://www.overbyte.be/frame_index.html?redirTo=/blog_source_code.html

These 2 components make using named pipes incredibly easy, and named pipes are great for inter-process communication (IPC).

His website is here. Look for ‘Pipes.zip’. The description from the source is: // Description : Set of client and server named pipe components for Delphi, as // well a console pipe redirection component.

Also, Russell helped me out on Experts-Exchange with using an older version of this component to work in a console app to send/receive messages over named pipes. This may help as a guide in getting you up and running with using his components. Please note, that in a VCL app or service, you don’t need to write your own message loop as I did in this console app.

program CmdClient; {$APPTYPE CONSOLE}  uses   Windows, Messages, SysUtils, Pipes;  type   TPipeEventHandler =  class(TObject)   public      procedure  OnPipeSent(Sender: TObject; Pipe: HPIPE; Size: DWORD);   end;  procedure TPipeEventHandler.OnPipeSent(Sender: TObject; Pipe: HPIPE; Size: DWORD); begin   WriteLn('On Pipe Sent has executed!'); end;  var   lpMsg:         TMsg;   WideChars:     Array [0..255] of WideChar;   myString:      String;   iLength:       Integer;   pcHandler:     TPipeClient;   peHandler:     TPipeEventHandler;  begin    // Create message queue for application   PeekMessage(lpMsg, 0, WM_USER, WM_USER, PM_NOREMOVE);    // Create client pipe handler   pcHandler:=TPipeClient.CreateUnowned;   // Resource protection   try      // Create event handler      peHandler:=TPipeEventHandler.Create;      // Resource protection      try         // Setup clien pipe         pcHandler.PipeName:='myNamedPipe';         pcHandler.ServerName:='.';         pcHandler.OnPipeSent:=peHandler.OnPipeSent;         // Resource protection         try            // Connect            if pcHandler.Connect(5000) then            begin               // Dispatch messages for pipe client               while PeekMessage(lpMsg, 0, 0, 0, PM_REMOVE) do DispatchMessage(lpMsg);               // Setup for send               myString:='the message I am sending';               iLength:=Length(myString) + 1;               StringToWideChar(myString, wideChars, iLength);               // Send pipe message               if pcHandler.Write(wideChars, iLength * 2) then               begin                  // Flush the pipe buffers                  pcHandler.FlushPipeBuffers;                  // Get the message                  if GetMessage(lpMsg, pcHandler.WindowHandle, 0, 0) then DispatchMessage(lpMsg);               end;            end            else               // Failed to connect               WriteLn('Failed to connect to ', pcHandler.PipeName);         finally            // Show complete            Write('Complete...');            // Delay            ReadLn;         end;      finally         // Disconnect event handler         pcHandler.OnPipeSent:=nil;         // Free event handler         peHandler.Free;      end;   finally      // Free pipe client      pcHandler.Free;   end;  end.