Re: How to reset 'end_error' using text_io?

Re: How to reset 'end_error' using text_io?

[Dave Colla rd x7468]

In <25h05c$3lv@neomimsy.cs.umd.edu> alex@cs.umd.edu (Alex Blakemore) writes:

>In article <fmoore.8@dseg.ti.com> fmoore@dseg.ti.com (Freeman L. Moore) writes
:
>> So, how can io_exceptions.end_error on standard input be cleared
>> permitting subsequent GETs to continue reading?

>text_io.skip_line I believe.

nope.  end_error means end of file -- skip_line just skips to the 
next line.

The following works, though vax specific:

  open(file => f,mode => in_file, name => "SYS$OUTPUT");
  loop
    begin
      get_line(f, buf, last);
      put_line("got " & buf(1..last));
    exception
      when end_error => 
        close(f);
        open(file => f,mode => in_file, name => "SYS$OUTPUT");
    end;
  end loop;

instead of sys$output you could use text_io.name(text_io.standard_output)
which might be more portable

--Thor
dlc@ddsdx2.jhuapl.edu

Re: How to reset 'end_error' using text_io?

[Michael Feldman]

In article <25h05c$3lv@neomimsy.cs.umd.edu> alex@cs.umd.edu (Alex Blakemore) wr
ites:
>In article <fmoore.8@dseg.ti.com> fmoore@dseg.ti.com (Freeman L. Moore) writes
:
>> So, how can io_exceptions.end_error on standard input be cleared
>> permitting subsequent GETs to continue reading?
>
>text_io.skip_line I believe.
>-- 
Would that it were (portably) so. Trouble is, that the End_Error was
raised because you bumped into EOF, which has a nasty tendency of causing
the file to be closed. And since you can't reopen Standard_Input, you
are stuck, at least in my experience (your implementation mileage may
vary).

My guess is that if you really need to do this, you could open the
file as a named file associated with the device. Then you could (maybe)
Reset it. We had this discussion on the net about a year ago when my
students got burned by an incorrect example of mine, showing a handler
for End_Error that tried to keep going in the file. Tilt. I think the
upshot of the thread was that no solution will be portable.

Oh well.

Mike Feldman
------------------------------------------------------------------------
Michael B. Feldman -  co-chair, SIGAda Education Committee
Professor, Dept. of Electrical Engineering and Computer Science
The George Washington University -  Washington, DC 20052 USA
202-994-5253 (voice) - 202-994-0227 (fax) - mfeldman@seas.gwu.edu (Internet)
"We just changed our CONFIG.SYS, then pressed CTRL-ALT-DEL. It was easy."
-- Alexandre Giglavyi, director Lyceum of Information Technologies, Moscow.
------------------------------------------------------------------------

Re: How to reset 'end_error' using text_io?

[dog.ee.lbl.gov!agate!spool.mu.edu!howland.reston.ans.net!europa.eng.gtefs]

In article <fmoore.8@dseg.ti.com> fmoore@dseg.ti.com (Freeman L. Moore) writes:
> So, how can io_exceptions.end_error on standard input be cleared
> permitting subsequent GETs to continue reading?

then I replied
>text_io.skip_line I believe.

then Thor set me straight
> nope.  end_error means end of file -- skip_line just skips to the next line.
 
OK, I was remembering using skip_line to solve a similar problem, when data_err
or
was raised on syntactically incorrect input using float_io.

Thor again:
> The following works, though vax specific: 
>   open(file => f,mode => in_file, name => "SYS$OUTPUT");
>   loop
>     begin
>       get_line(f, buf, last);
>       put_line("got " & buf(1..last));
>     exception
>       when end_error => 
>         close(f);
>         open(file => f,mode => in_file, name => "SYS$OUTPUT");
>     end;
>   end loop;

> instead of sys$output you could use text_io.name(text_io.standard_output)

you might even have better luck if you use sys$input or text_io.standard_input.
 8^)


another thing to try would be to use
   text_io.reset (text_io.standard_input)
instead of closing and reopening the file.
unfortunately, I don't have access to the great VAX compiler to test this out.


-- 
Alex Blakemore       alex@cs.umd.edu        NeXT mail accepted
--------------------------------------------------------------
"Without an engaged and motivated human being at the keyboard,
the computer is just another dumb box."      William Raspberry

Re: How to reset 'end_error' using text_io?

[cis.ohio-state.edu!magnus.acs.ohio-state.edu!math.ohio-state.edu!howland.]

In <25jteg$6e7@neomimsy.cs.umd.edu> alex@cs.umd.edu (Alex Blakemore) writes:
>In article <fmoore.8@dseg.ti.com> fmoore@dseg.ti.com (Freeman L. Moore) writes
:
>> So, how can io_exceptions.end_error on standard input be cleared
>> permitting subsequent GETs to continue reading?

>then I replied
>>text_io.skip_line I believe.

>then Thor set me straight
>> nope.  end_error means end of file -- skip_line just skips to the next line.
> 
>OK, I was remembering using skip_line to solve a similar problem, when data_er
ror
>was raised on syntactically incorrect input using float_io.

>you might even have better luck if you use sys$input or text_io.standard_input
. 8^)

Oh.  Of course.

>another thing to try would be to use
>   text_io.reset (text_io.standard_input)
>instead of closing and reopening the file.


sorry Alex, but nope again.  text_io.standard_input is a function
text_io.reset has one in_out parameter

and text_io.file_type is limited private so you can't play games with
storing text_io.standard_input into a variable and calling reset on 
that variable.

>unfortunately, I don't have access to the great VAX compiler to test this out.

poor Alex.  whatcha up to these days?

--Thor
dlc@ddsdx2.jhuapl.edu

Re: How to reset 'end_error' using text_io?

[Dave Collard x7468]

In <1993Aug27.023237.20864@seas.gwu.edu> mfeldman@seas.gwu.edu (Michael Feldman
) writes:

>In article <25h05c$3lv@neomimsy.cs.umd.edu> alex@cs.umd.edu (Alex Blakemore) w
rites:
>>In article <fmoore.8@dseg.ti.com> fmoore@dseg.ti.com (Freeman L. Moore) write
s:
>>> So, how can io_exceptions.end_error on standard input be cleared
>>> permitting subsequent GETs to continue reading?
>>
>>text_io.skip_line I believe.
>>-- 
>Would that it were (portably) so. Trouble is, that the End_Error was
>raised because you bumped into EOF, which has a nasty tendency of causing
>the file to be closed. And since you can't reopen Standard_Input, you
>are stuck, at least in my experience (your implementation mileage may
>vary).

Hmmm.  you cant reopen standard_input, but you can reopen a file with
the same name as it (see below);

>My guess is that if you really need to do this, you could open the
>file as a named file associated with the device. Then you could (maybe)
>Reset it. We had this discussion on the net about a year ago when my

So is my solution portable??  anyone who can try it on their machines?
it works on the VAX:

with text_io; 
procedure enderror is
  buf : string(1..80); last : natural;
  f : text_io.file_type;
begin
  text_io.open(file => f,
               mode => text_io.in_file, 
               name => text_io.name(text_io.standard_input));
  text_io.set_input(f);
  loop
    begin
      text_io.get_line(buf, last);
      text_io.put_line("got " & buf(1..last));
    exception
      when text_io.end_error => 
        text_io.reset(f);
    end;
  end loop;
end;

thanks to R_Tim_Coslet@cup.portal.com for suggesting reset(f)
instead of close(f), open(...)

thanks to Alex Blakemore for pointing out that i was getting
the name of standard_output instead of input (which was
the same on the vax normally)

--Thor
dlc@ddsdx2.jhuapl.edu

Re: How to reset 'end_error' using text_io?

[Keith Shillington]

(Many educated and honorable persons) write:
>>> So, how can io_exceptions.end_error on standard input be cleared
>>> permitting subsequent GETs to continue reading?
(And many other elided conversations)

The problem being that
  Text_IO.End_Of_File
has become true.  This is equivalent to
  Text_IO.End_Of_File(Current_Input)
                      -- originally defaulted to Text_IO.Standard_Input
So, lets assume that we have an F such that
  F : Text_IO.File_Type;
If we are to
  Text_IO.Open(F,Text_IO.In_Mode,"SYS$INPUT");
  Text_IO.Set_Input(F);
Then the desired result is achieved.  Of course for a more portable
solution, "SYS$INPUT" is replaced by a constant defined in a system
specific package...

--/*No Problem*/--

-- 
  Keith Shillington               /---------\   "No matter where you go,
email: shilling@source.ASSET.com   /=======\     There you are."
voice: (619) 944-5134               /_____\          -- Buckaroo Banzaii
fax  : (619) 944-7089                 | |         office: (301) 924-0050