How do I write to StdOut from a GUI app started from the command line?

Question

I am writing a standard windows app in Delphi 7.

If I was writing a console app, I can call the following to output to the cmd line or output file.

write         


        

Answer 1

I did summarize this topic in a report with a running script too:

http://www.softwareschule.ch/download/maxbox_starter70.pdf as a second backup:

https://www.slideshare.net/maxkleiner1/nogui-maxbox-starter70

the main routine has a nativewriteline to separate from writeline:

 for it:=1 to 50 do if IsPrime(it) then NativeWriteln(IntToStr(it)+' is prime');

Answer 2

Call AllocConsole to avoid the error 105.

Answer 3

I'm not quite sure what you are trying to achieve.
As I understood the question one way could be

program Project1;
{$APPTYPE CONSOLE}

uses
  Forms, Classes, Windows,
  Unit1 in 'Unit1.pas' { Form1 } ;
{$R *.res}

var
  Finished: Boolean;
  Input: String;

function IsConsoleMode(): Boolean;
var
  SI: TStartupInfo;
begin
  SI.cb := SizeOf(TStartupInfo);
  GetStartupInfo(SI);
  Result := ((SI.dwFlags and STARTF_USESHOWWINDOW) = 0);
end;

procedure HandleInput;
begin
  Finished := Input = 'quit';
  if not Finished then
  begin
    Writeln('Echo: ' + Input);
  end
  else
    Writeln('Bye');
end;

begin
  if IsConsoleMode then
  begin
    Finished := false;
    Writeln('Welcome to console mode');
    while not Finished do
    begin
      readln(Input);
      HandleInput;
    end;
  end
  else
  begin
    Writeln('Entering GUI Mode');
    FreeConsole;
    Application.Initialize;
    Application.MainFormOnTaskbar := True;
    Application.CreateForm(TForm1, Form1);
    Application.Run;
  end;

end.

Answer 4

There's no reliable way for a GUI subsystem application to attach to the console of its parent process. If you try to do so you end up with two active processes sharing the same console. This leads to no end of trouble.

The alternative, whilst retaining just a single executable, as suggested by bummi, is to have a console app that frees its console if it is asked to run in GUI mode. This is a better approach, but leads to a console window flashing up, and then closing, when you want to run in GUI mode.

The best discussion of the subject that I have come across on Stack Overflow is Rob Kennedy's superb answer: Can one executable be both a console and GUI application?

I believe, from what you say in comments, that the best option for you is to create two separate executables. One for the GUI subsystem, and one for the console subsystem. This is the approach taken by:

• Java: java.exe, javaw.exe.
• Python: python.exe, pythonw.exe.
• Visual Studio: devenv.com, devenv.exe.

Yes you have to ship multiple executables. But doing so gives the user the best experience.

Answer 5

FWIW, I played around with this problem and happened upon AttachConsole which seems to do the trick. The only problem I ran into with my code is that the program won't give the console up without an extra ENTER key or two. It's not real polished since I was trying to fix that problem and (kind of) gave up. Perhaps someone here will see it?

program writecon; uses windows, dialogs;

  function AttachConsole(dwProcessID: DWord): BOOL; stdcall; external 'kernel32.dll';

  function load_attach_console: boolean;
    begin
      Result := AttachConsole(-1);
    end;

  begin
    // the function requires XP or greater, you might want to check for that here.
    if load_attach_console = true then
      begin
        writeln;
        writeln('This is running in the console.');
        write('Press ENTER to continue.');
        readln;
        // from the linked page, you have to detach yourself from the console
        // when you're done, this is probably where the problem is.
        Flush(Output);
        Flush(Input);
        FreeConsole;
      end
    else
      MessageDlg('This is not running in the console.', mtInformation, [mbOk], 0);
  end.

Answer 6

AttachConsole does seem to work, as noted above it waits for ENTER.

However, the program is still a win prog and not a console program as far as dos sees it, and so cmd proceeds to the next command after launching it.

test.exe & dir

shows the dir listing first, then the output from test.exe

start /w test.exe & dir 

does work, and does not pause for ENTER key

BTW, the suggestion above: PostMessage(GetCurrentProcess,$0101,$0D,0); does the ENTER but is giving a bong noise.