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From: eachus@spectre.mitre.org (Robert I. Eachus)
Subject: Re: Exceptions:  Are they GOTOs?
Date: 1996/07/16
Message-ID: <EACHUS.96Jul16140913@spectre.mitre.org>#1/1
X-Deja-AN: 169297676
references: <brad.837052481@ss1> <4s4gic$etl@news.pacifier.com>
organization: The Mitre Corp., Bedford, MA.
newsgroups: comp.lang.ada
Date: 1996-07-16T00:00:00+00:00
List-Id: <comp.lang.ada>


In article <4s8jjs$1gu@felix.seas.gwu.edu> mfeldman@seas.gwu.edu (Michael Feldman) writes:

     (Lots of good stuff including:)

   > If I _forget_ to write correct code to test for end-of-file,
   > and unexpectedly hit the end of the file, Ada.Text_IO.End_Error
   > _will_ be raised. If that happens, it is because my code has a
   > bug in it - I forgot the test (or wrote it incorrectly).

    However, I'd like to point out that always checking for
end-of-file is also inappropriate.  The rule I use is that an
incorrectly structured file can cause End_Error, but reaching the end
of the file "normally" should always be handled by checking for
end-of-file.

    For example, suppose I am reading a table of city names and high
and low temperatures for the day:

     while not Text_IO.End_of_File(foo) loop
       begin 
         Get_Name_of_City
         Int_IO.Get(foo, High);
         Int_IO.Get(foo, Low);
         Skip_Line(foo);
       exception
         when Text_IO.End_Error => 
           Deal_With_Incomplete_Record;
           exit;
         ...
       end;

     end loop;
     ...

   ...

   If I get to this handler it is because the file ended in an
incomplete record.  Now oyu may argue that I should read each line
into a buffer, then process it.  I will usually operate that way, but
the point still remains: you will get End_Error if temperature data is
missing, but correct files will never cause an exception.


--

					Robert I. Eachus

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