[SOLVED] output redirection with unit crt inserts wrong char $0A and
$0D in outp
lazarus / 32-Linux

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Hartmut · 2019-02-04 20:14

I use FPC 3.0.4 on Linux (Ubuntu 18.04). If you run the following code
in a terminal console, you'll see 30 lines of 100 chars each:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i program
demo; {$mode objfpc}{$H+} uses crt; var s: string[255];    i:
integer; begins:=''; for i:=1 to 10 do  s:=s + '1234567890';for i:=1
to 30 do  writeln(i:2, ' ', s);end. 
But if you redirect the output like Code: [Select]demo >
outfile.txtyou'll have 2 strange things in your file (see attached
screenshot):
 - each line has wrongly inserted a Linefeed ($0A) after column 80
 - from line 13 on, each line is followed by an empty line, because it
ends with $0A0D instead of $0A

On Windows this problem does not exist, only on Linux. I found out,
that the "culprit" ist unit crt. If you omit unit crt, the problem
disappears. But my "real program" uses a couple of units, which
directly or indirectly use unit crt, so I can't avoid unit crt.

Question #1: is this a bug or "as designed"?

To avoid the problem I tried:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i
begincrt.WindMaxX:=2000;crt.WindMaxY:=dword(-1);s:=''; for i:=1 to 10
do  s:=s + '1234567890';for i:=1 to 30 do  writeln(i:2, ' ', s);end.
The redirected output now is correct, but now I get 2 Runtime errors:
Code: [Select]hg6@i3300:~$ demo > outfile.txt
Runtime error 216 at $0805D8D4
  $0805D8D4
  $0806EC5D

Runtime error 216 at $0805D888
  $0805D888
  $0806EC5DRuntime error 216 means "General Protection fault. The
application tried to access invalid memory space." 
 
Question #2: does anybody know how to avoid these runtime errors or
knows another way to avoid the $0A and $0D in the redirected output?
Thanks in advance.

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Hartmut · 2019-02-04 20:17

to provide a 2nd screenshot I had to use this reply because of the
maximum of 250 KB

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dbannon · 2019-02-04 21:49

I don't understand why crt is outputting a windows style line ending
on Linux.

But maybe you could provide your own line ending, do -

write('stuff' + LineEnding);   

Davo

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valdir.marcos · 2019-02-05 01:18

Quote from: Hartmut on February 04, 2019, 09:14:48 pmI use FPC 3.0.4
on Linux (Ubuntu 18.04). If you run the following code in a terminal
console, you'll see 30 lines of 100 chars each:
On Windows this problem does not exist, only on Linux. I found out,
that the "culprit" ist unit crt. If you omit unit crt, the problem
disappears. But my "real program" uses a couple of units, which
directly or indirectly use unit crt, so I can't avoid unit crt.

Question #1: is this a bug or "as designed"?
 
Question #2: does anybody know how to avoid these runtime errors or
knows another way to avoid the $0A and $0D in the redirected output?
Thanks in advance.
Quote from: dbannon on February 04, 2019, 10:49:22 pmI don't
understand why crt is outputting a windows style line ending on Linux.
But maybe you could provide your own line ending, do -
write('stuff' + LineEnding);Shouldn't this behaviour be reported as a
bug?

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Handoko · 2019-02-05 03:40

I think it is not bug.

Quote from: Hartmut on February 04, 2019, 09:14:48 pm - each line has
wrongly inserted a Linefeed ($0A) after column 80
I remember in my old computer, the width of DOS text mode is 80. It
seems the crt unit will automatically add chr($0A) when the output
reach 80 characters from the left.

Quote from: Hartmut on February 04, 2019, 09:14:48 pm - from line 13
on, each line is followed by an empty line, because it ends with $0A0D
instead of $0A
https://en.wikipedia.org/wiki/Text_mode#PC_common_text_modes

The common text mode for VGA is 80x25. OP's code generate 2 output
lines for each single writeln. So when it reaches the line 13th, the
total screen output is the line 26th. And the crt will automatically
added an extra chr($0D).

Quote from: Hartmut on February 04, 2019, 09:14:48 pmThe redirected
output now is correct, but now I get 2 Runtime errors:
Code: [Select]hg6@i3300:~$ demo > outfile.txt
Runtime error 216 at $0805D8D4
  $0805D8D4
  $0806EC5D

crt.WindMaxX:=2000;
crt.WindMaxY:=dword(-1);
I'm not familiar with WindMax, but it seems that the value must be
below 80x25.

Quote from: Hartmut on February 04, 2019, 09:14:48 pmQuestion #2: does
anybody know how to avoid these runtime errors or knows another way to
avoid the $0A and $0D in the redirected output? Thanks in advance.

I remember I ever heard there are crt unit alternatives.

But why those behaviors don't appear on Windows? I don't know. Maybe
it is OS depended.

--edit--

I checked the initialization code of crt unit. I can't understand but
maybe you can understand and do a temporary redirect back to normal
standard output when it writes to a file (if ParamCount > 0).

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i
Initialization{$ifdef debugcrt}  Assign(DebugFile,'debug.txt'); 
ReWrite(DebugFile);{$endif}  { Redirect the standard output } 
assigncrt(Output);  Rewrite(Output); 
TextRec(Output).Handle:=StdOutputHandle;  assigncrt(Input); 
Reset(Input);  TextRec(Input).Handle:=StdInputHandle;{ Are we
redirected to a file ? }  OutputRedir:=
IsAtty(TextRec(Output).Handle)<>1;{ does the input come from another
console or from a file? }  InputRedir := 
 (IsAtty(TextRec(Input).Handle)<>1) or   (not OutputRedir and   
(TTYName(TextRec(Input).Handle) <> TTYName(TextRec(Output).Handle)));{
Get Size of terminal and set WindMax to the window }  GetConsoleBuf; 
WindMinX:=1;  WindMinY:=1;  WindMaxX:=ScreenWidth; 
WindMaxY:=ScreenHeight;  WindMax:=((ScreenHeight-1) Shl
8)+(ScreenWidth-1);{Get Current X&Y or Reset to Home}  if OutputRedir
then   begin     CurrX:=1;     CurrY:=1;   end  else   begin   { Set
default Terminal Settings }     SetRawMode(True);   { Get current X,Y
if not set already }     GetXY(CurrX,CurrY);     if (CurrX=0) then   
 begin        CurrX:=1;        CurrY:=1;        ttySendStr(#27'[H'); 
   end;   {Reset Attribute (TextAttr=7 at startup)}     
ttySendStr(#27'[m');    end;

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GAN · 2019-02-05 04:37

A String variable declared with a length specifier will always be a
ShortString regardless of the compiler setting for String alias.
http://wiki.freepascal.org/String

But this does not solve the problem.

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Hartmut · 2019-02-05 12:03

Thanks a lot to all for your numerous replies. I will answer them one
by one. Please keep in mind, that the wronlgly inserted chars $0A and
$0D only appear, when the output is redirected. Without redirection
everything is ok. And the problem is only in Linux, not on Windows.

Quote from: dbannon on February 04, 2019, 10:49:22 pmBut maybe you
could provide your own line ending, do -
write('stuff' + LineEnding);   
I tried it and it makes no difference.

Quote from: valdir.marcos on February 05, 2019, 02:18:55 amShouldn't
this behaviour be reported as a bug?
That was my question...

Quote from: Handoko on February 05, 2019, 04:40:59 amI think it is not
bug.

I remember in my old computer, the width of DOS text mode is 80. It
seems the crt unit will automatically add chr($0A) when the output
reach 80 characters from the left.
...
The common text mode for VGA is 80x25. OP's code generate 2 output
lines for each single writeln. So when it reaches the line 13th, the
total screen output is the line 26th. And the crt will automatically
added an extra chr($0D).
This sounds convincing. But why does this behavior only occur when the
output is redirected? And why not on Windows?

Quote from: Handoko on February 05, 2019, 04:40:59
amcrt.WindMaxX:=2000;
crt.WindMaxY:=dword(-1);
I'm not familiar with WindMax, but it seems that the value must be
below 80x25.
If this value must be below 80x25, then this could not be a solution
for my problem. But WindMaxX and WindMaxY are of type dword. They
replace the deprecated variable 'WindMax', which had type Word. So I
can't believe hat they must be below 80x25.

Quote from: Handoko on February 05, 2019, 04:40:59 amI remember I ever
heard there are crt unit alternatives.
My "real program" uses a couple of units, which directly or indirectly
use unit crt, so I can't avoid unit crt.

Quote from: Handoko on February 05, 2019, 04:40:59 amI checked the
initialization code of crt unit. I can't understand but maybe you can
understand and do a temporary redirect back to normal standard output
when it writes to a file (if ParamCount > 0).
Thank you for providing this code. I checked it, but as far as I
understand, I see nothing which is wrong or could be adapted to solve
my problem.

Quote from: GAN on February 05, 2019, 05:37:57 amA String variable
declared with a length specifier will always be a ShortString
regardless of the compiler setting for String alias.
http://wiki.freepascal.org/String
But this does not solve the problem.
That's true.

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lucamar · 2019-02-05 13:49

I'm not sure whether this will work but try doing

Code: [Select]Assign(Output, ''); Rewrite(Output)
at the start of your program.

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Hartmut · 2019-02-05 18:55

Quote from: lucamar on February 05, 2019, 02:49:54 pmI'm not sure
whether this will work but try doing
Code: [Select]Assign(Output, ''); Rewrite(Output)at the start of your
program.

This works! Thank you very much for that idea, lucamar. Now my program
starts like:

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i {$IFDEF
LINUX}function ConOutRedirected: boolean;   {checks if Console Output
was redirected}   begin   exit(termio.IsATTY(Output) = 0); //
0=redirected / 1=normal   end; ...    if ConOutRedirected then  
 begin Assign(Output, ''); Rewrite(Output); end; {$ENDIF}

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lucamar · 2019-02-05 19:31

It's an old TP/BP "trick" and since normally I don't use crt I wasn't
sure it would work. Mighty glad it did