Mail #11309

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From: Waldek Hebisch
Subject: EOF is not true on reset empty file
Date: 30 Jan 2005, 02:05:50

Tom Schneider wrote:
> One of my programs, which I have used with many compilers in the past,
> started an odd behavior as soon as I compiled with GPC.  I rooted down
> to what the cause was and found this:
> 
> EOF is not true on a reset empty file.
> 
<snip>
> Is this standard behavior for Pascal?  I thought that if you reset
> an file, it would be at eof.  Where else could it be?
> 

There is a little tricky point here: the standard requires read from
text file to give eoln and a space character before eof. So GPC
runtime adds a newline before eof if original file contained no
newline. That was wrong for empty file. The following patch should
fix the problem (apply it relatively to gpc-20041218/p directory):

--- rts/files.pas.bb	2005-01-30 00:55:45.498296856 +0100
+++ rts/files.pas	2005-01-30 00:55:51.371404008 +0100
@@ -1259,7 +1259,10 @@
 end;
 
 procedure ReadBuffer (f: GPC_FDR);
+var WasRead: boolean;
 begin
+  WasRead := not f^.Status.Unread;
+  f^.Status.Unread := false;
   f^.BufPos := 0;
   if f^.ReadFunc <> nil then
     begin
@@ -1277,7 +1280,8 @@
         it prevents detecting whether there actually is an EOLn in the file. }
       if f^.BufSize <> 0 then
         f^.Status.LastEOLn := f^.BufPtr^[f^.BufSize - 1] = NewLine
-      else if ((RTSOptions and ro_SP_EOLn) <> 0) and f^.Status.Text and not f^.Status.LastEOLn then
+      else if ((RTSOptions and ro_SP_EOLn) <> 0) and f^.Status.Text
+                and not f^.Status.LastEOLn and WasRead then
         begin
           f^.Status.LastEOLn := True;
           f^.BufPtr^[0] := NewLine;
@@ -1716,7 +1720,6 @@
   n: SizeType;
 begin
   if not CheckReadableNotEOF (f) then Exit;
-  f^.Status.Unread := False;
   f^.Status.Undef := False;
   f^.Status.LGet := False;
   { @@ this different treatment is suspicious }

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