Because I have no idea how to do this properly (It has been a hundred years since I last used this form of file IO in Pascal) I have done the following hack, just to get it running somehow but now I wonder what would be the proper way to do this. How can I do something like a hypothetical IsOpen(StdOut) the proper way? This is what I have done but I don't like it:

implementation
var
  HasOutput: Boolean = True;
procedure log(const s: String);
begin
  if HasOutput then
    writeln(s);
end;
initialization
  try
    writeln();
  except
    HasOutput := False;
  end;
end.

What about using IsConsole? This indicates if the app has been compiled with
{$apptype console}.

Your solution has the advantage of being simple and cross-platform.

On windows this works for me:

function IsConsoleOpen:boolean;
var mode:longword;
begin
result:=GetConsolemode(GetStdHandle(STD_OUTPUT_HANDLE),mode);
end;

Ludo

There is an IsConsole boolean in the system unit AFAIK.

Bart

That was my first line ;)

I should read better...

Bart

Hi Bernd

The subject indicates that you look for a solution for normal files but your example indicates that you what to detect the console. So I add my solutions for both.

function HasConsole: Boolean;
// This function tests if there is a console. If GetStdHandle() reports that there is a console when in fact there
// isn't (as in Matlab R2008a), we still need to check if writing to the output handle works to get the right answer.
begin
 // In Free Pascal V2.4.0 STD_*_HANDLE seem to be defined in a way that it is not directly usable for WIN64 target. In
 // the source rtl\win\syswin.inc, procedure SysInitStdIO() there is Cardinal() (which is the type of STD_*_HANDLE in
 // Delphi) around the handles.
 Result := ((GetStdHandle({$IFDEF WIN64}Cardinal{$ENDIF}(STD_INPUT_HANDLE))   0) and
            (GetStdHandle({$IFDEF WIN64}Cardinal{$ENDIF}(STD_OUTPUT_HANDLE))  0));
 if (Result) then
   try
     write('');
   except
     on EInOutError do begin
       Result := False;
     end;
   end;
end;

For normal files I have:

function FileIOMode(var F: Text): Word;
begin
 case TTextRec(F).Mode of
   fmClosed,
   fmInput,
   fmOutput,
   fmInOut : Result := TTextRec(F).Mode;
   // There is no 'fmUnknown' to indicate this ;-) I assume this mean 'handle never used before'.
   else      Result := fmClosed;
 end;
end;

(Same function for untyped files: replace 'Text' by 'file' and ' TTextRec' by 'TFileRec')

And in the code you can write

If (FileIOMode(Foo)  fmClosed) then
...

Regards

Michael

2011/7/15 Michael Müller :

The subject indicates that you look for a solution for normal files but your example indicates that you what to detect the console. So I add my solutions for both. [...]

This is helpful information! Normally I would try do do file IO with streams. Only the console problem made me realize again that it seems I have completely forgotten everything I ever knew about the File and Text types and their internal mechanisms.

Bernd

Hmm... I don't know whether I understand your intension correctly, but do you know about the unit "IOStream"?

See here: http://www.freepascal.org/docs-html/fcl/iostream/index.html

Regards,
Sven

2011/7/15 Sven Barth :

Hmm... I don't know whether I understand your intension correctly, but do you know about the unit "IOStream"?

I know about streams and use all sorts of streams every day, but what i don't know very much about is the old pascal-ish way of handling files that I have not used for ages now (assign(), rewrite() and friends)