Re: eoln and eof - Gpc

25 Apr 2002


      CBFalconer wrote:
...
Emil Jerabek wrote:
...
the RTS sometimes fails to report EOLn before EOF, when
a new-line character is missing in the file. For example,
this simple program

program BufferedInput (Output, F);
var
  F: Text;
  Buffer: String (100);
begin
  Reset (F);
  while not EOF (F) do begin
    while not EOLn (F) do begin
      Read (F, Buffer);
      WriteLn ('read: `', Buffer, '''')
    end;
    WriteLn ('(end of line)');
    ReadLn (F)
  end;
  WriteLn ('(end of file)')
end.

produces

Input file `F': test
read: `first line'
(end of line)
read: `second line, with no terminator'
./a.out: attempt to read past end of file `test' (error #454 at 8049c73)

on this input (where line 2 doesn't end with <LF>):

first line
second line, with no terminator

And it is absolutely correct, IMO.  Let's rewrite a portion doing
the standard expansions:
...
while not EOF (F) do begin
    while not EOLn (F) do begin
      Read (F, Buffer);
      WriteLn ('read: `', Buffer, '''')
    end;
  Write('(end of line)');
  writeln;
  WHILE NOT eoln(F) DO get(f);
  get(f);  (* <<<<< THIS triggers the error, as it should *)

No, it doesn't. Maybe its not aparent from the original program output,
but the run-time error is triggered already by the call to EOLn. (Try
a debugger, if you don't believe this.)
Anyway, the last `get' in your modification should _not_ generate any error,
it should bypass the end-of-line character (reported as ' ' in F^), and only
after that `get' EOF (F) becomes true, F^ undefined, and get (F) invalid.
Also note that both programs work if you declare `Buffer: Char;' instead 
of a string.
...
...
end;
The cure is to write "IF NOT eof(f) THEN readln(f);"  The "(end of
line)" is probably lying about in some internal buffers and failed
to get completely flushed, which is an entirely different run-time
failing.
GPC's run-time system doesn't buffer any output, AFAIK.
Emil Jerabek
...
-- 
Chuck F (cbfalconer@yahoo.com) (cbfalconer@worldnet.att.net)
   Available for consulting/temporary embedded and systems.
   http://cbfalconer.home.att.net  USE worldnet address!