Launching an external executable.

Hi

ShellExecute is the best method in Win 95/98/NT to execute any file.  The benefit is that it doesn't have to be an EXE file.  It can be DOC, BMP, etc.

The syntax is:

(To answer your question: you have to include the "ShellApi" unit.)

ShellExecute(Self.Handle, 'open', PChar('C:\Windows\Notepad.exe'), PChar('C:\autoexec.bat'), nil, SW_NORMAL);

I use Self.Handle, where Self is the main form, so this is the same as "Application.MainForm.Handle".  This parameter is the window handle of the calling app that can receive error messages if ShellExecute fails, etc.  You can also use GetDesktopWindow.

Another useful way of starting an app is CreateProcess:

var
  ProcessInfo: TProcessInformation;
  StartUpInfo: TStartUpInfo;
begin
  ZeroMemory(@StartUpInfo, SizeOf(TStartUpInfo));
  with StartUpInfo do
    begin
      cb := SizeOf(TStartUpInfo);
      dwFlags := STARTF_USESHOWWINDOW or STARTF_USESTDHANDLES;
      wShowWindow := SW_SHOWNORMAL;;
    end;
  CreateProcess(nil, PChar('C:\Windows\Notepad.exe C:\autoexec.bat'), nil, nil, True, NORMAL_PRIORITY_CLASS, nil, nil, StartUpInfo, ProcessInfo);
end;

The benefits of CreateProcess are as follows:

(1)  You can close Notepad politely:

function ThreadWndProc(hWnd: HWND; lParam: LParam): Bool; stdcall;
begin
  // lParam is WM_CLOSE, because that's what we send in when
  // we call EnumThreadWindows (below).
  // Thus, the following will send WM_CLOSE to the window.
  SendMessage(hWnd, lParam, 0, 0);

  // Return True to continue enumeration.
  Result := True;
end;

if not (EnumThreadWindows(ProcessInfo.dwThreadId, @ThreadWndProc, WM_CLOSE)) then
  ShowMessage('EnumThreadWindows failed!');
 

(2)  You can force Notepad to close (unsaved changes in Notepad are lost):

  TerminateProcess(ProcessInfo.hProcess, 0);


(3)  You can execute Notepad & wait for it to terminate:

  ZeroMemory(@StartUpInfo, SizeOf(TStartUpInfo));
  with StartUpInfo do
    begin
      cb := SizeOf(TStartUpInfo);
      dwFlags := STARTF_USESHOWWINDOW or STARTF_USESTDHANDLES;
      wShowWindow := SW_SHOWNORMAL;;
    end;
  if (CreateProcess(nil, PChar('C:\Windows\Notepad.exe C:\autoexec.bat'), nil, nil, True, NORMAL_PRIORITY_CLASS, nil, nil, StartUpInfo, ProcessInfo)) then
    begin
      WaitForSingleObject(ProcessInfo.hProcess, INFINITE);
      ShowMessage('Finished');
    end;


I usually use ShellExecute because it's pretty simple & can be used on any file (if the file extension is registered).  You can use WinExec, but it's maintained only for compatibility with older versions of Windows.  WinExec will call CreateProcess anyway.

Cheers,
JB