Reading the output file of ShellExecute() in Delphi 2010?

Question

I use the ShellExecute command to run an exe file which gets an input text file and returns an output text file. I've written it like this:

ShellExecute(mainFormHandle, 'open', 'Test.exe',
    'input.txt output.txt', nil, sw_shownormal);

//Read the output file...
S_List.LoadFromFile('output.txt');
Writeln(S_List[0])

I provide the input.txt file before running this command. In each run of my program, the input file changes and so does the output file.

The problem is this: I can't see the changes in the output file! The line written in the console is from the previous file, not the newly changes one. I mean, the file in the explorer is changed but the file that I read is still the old file.

It seems a little weird, but I was wondering is there any way to refresh the output file before reading it? Or I am missing something here?

Thanks in advance.

Answer 1

ShellExecute does not wait for your program to finish work. This is what happens:

• Test.exe starts
• you read in output.txt
• Test.exe writes new output.txt

Try something like this:

var
  StartUpInfo : TStartUpInfo;
  ProcessInfo : TProcessInformation;
  CreationFlags : Cardinal;
begin
  FillChar(StartUpInfo, SizeOf(TStartupInfo),0);
  StartupInfo.cb := SizeOf(TStartupInfo);
  CreationFlags := Normal_Priority_Class;

  if CreateProcess(nil, 'test.exe input.txt output.txt',
               nil, nil, False, CreationFlags,
               nil, 0, StartupInfo, ProcessInfo) then
  begin
    WaitforSingleObject(ProcessInfo.HProcess, INFINITE);
    CloseHandle(ProcessInfo.HProcess);

    //Read the output file...
    S_List.LoadFromFile('output.txt');
  end;

With WaitForSingleObject you can wait until a process finishes work.