From: anon@anon.org (anon)
Subject: Re: unsigned type
Date: Sat, 11 Jul 2009 20:20:48 GMT
Date: 2009-07-11T20:20:48+00:00 [thread overview]
Message-ID: <Au66m.436787$4m1.76210@bgtnsc05-news.ops.worldnet.att.net> (raw)
In-Reply-To: ff104286-de81-4bd3-bfef-70cbae1d16df@v2g2000vbb.googlegroups.com
Zero length are defined in Ada a null length and the common use in source
code is either a string value of "" or any string with a null range, that is
where the Upper bounds is less than the lower bound, such as ( 1 .. 0 ) or
( 5 .. 3 ), but to me the idea that ( 1 .. 0 ) or ( -5 .. -7 ) is a valid null
string, is wrong. Both indexes should be of the type positive, which makes
the ( 1..0 ) that is use in the RM illegal. But some here and the GNAT compiler
says the ( 1 .. 0 ) and ( -5 .. -7 ) are both valid in the source code. A
string with the range of ( -5 .. -7 ) looks like bad C coding anfd that's not
Ada.
The problem is at runtime the system checks the Lower bounds for a valid
type first, but it only checks the Upper bound type, after it determines that
the value is not a null range. So, to the runtime a ( 1 .. -100 ) is a valid
runtime, and that seams wrong. Especially, since Ada is known for it strong
"Type Checking" it seams logical to first check both indexes foe a valid type,
then the null range second. With the third being for a valid subscript range.
See post "getting back to null range' for an example program.
In <ff104286-de81-4bd3-bfef-70cbae1d16df@v2g2000vbb.googlegroups.com>, =?ISO-8859-1?Q?Hibou57_=28Yannick_Duch=EAne=29?= <yannick_duchene@yahoo.fr> writes:
>On 29 juin, 10:00, a...@anon.org (anon) wrote:
>> -- 'A' is a zero length string, A'Last = 0, and
>> -- put_line ( A ( A'First .. A'Last ) ) ;
>> -- does not raise an Constraint_Error even though in
>> -- this case it translate to:
>> -- put_line ( A ( 0 .. 0 ) ) ;
>> A : String := "" ;
>> Since you can have zero length string , the index is Natual instead of Positive,
>> because zero is in Natural but is not define in Positive. Even though the
>> Standard package define String index as a Positive type.
>
>The length of a string is Natural, the index type Positive, as long as
>lowest bound is 1.
>
>A zero length string does not have any valid index. Using strings,
>unless I can assert the length is greater than zero, I always check
>the length before any attemp to use its 'First and 'Last attributes.
>Conceptually, when a string is zero length, at least one of its bound
>is not in the valid range of its index type, and any way, none of its
>bound would be a valid index in the string.
>
>There is a precondition to access both bound or to access element of a
>string by index : this precondition as that its length should be
>greater than zero.
>
>Printing a zero length string does not imply attempting to print
>chracters in index range 1 .. 0, but may be instead properly handled
>by simple not accessing the string and simply not printing anything,
>providing the length has been previously known to be zero.
next prev parent reply other threads:[~2009-07-11 20:20 UTC|newest]
Thread overview: 113+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-06-28 15:36 unsigned type Rob Solomon
2009-06-28 15:45 ` Florian Weimer
2009-06-28 15:48 ` Albrecht Käfer
2009-06-28 17:56 ` anon
2009-06-28 19:17 ` Ludovic Brenta
2009-06-28 23:08 ` anon
2009-06-29 0:19 ` tmoran
2009-06-29 8:00 ` anon
2009-06-29 9:56 ` Jean-Pierre Rosen
2009-06-29 10:21 ` Ludovic Brenta
2009-06-29 11:23 ` sjw
2009-06-29 12:07 ` Jean-Pierre Rosen
2009-06-29 20:06 ` anon
2009-06-29 19:31 ` anon
2009-06-29 21:49 ` Georg Bauhaus
[not found] ` <zuKdneNYxfFNLNTXnZ2dnUVZ_t2dnZ2d@earthlink.com>
2009-06-30 11:29 ` anon
2009-06-30 12:19 ` Ludovic Brenta
2009-06-29 20:19 ` anon
2009-06-29 20:41 ` Ludovic Brenta
2009-06-29 22:15 ` Georg Bauhaus
2009-06-29 23:08 ` Adam Beneschan
2009-06-29 23:11 ` Adam Beneschan
2009-06-30 12:39 ` Martin
2009-06-29 10:25 ` Georg Bauhaus
2009-06-29 20:02 ` anon
2009-06-29 22:08 ` Georg Bauhaus
2009-06-30 23:01 ` Randy Brukardt
2009-06-30 13:46 ` Jean-Pierre Rosen
2009-06-30 15:22 ` Adam Beneschan
2009-06-30 15:59 ` Albrecht Käfer
2009-06-30 16:59 ` Adam Beneschan
2009-06-30 17:44 ` Albrecht Käfer
2009-06-30 18:13 ` Robert A Duff
2009-06-30 18:16 ` Albrecht Käfer
2009-06-30 23:48 ` anon
2009-07-01 1:39 ` Adam Beneschan
2009-07-02 19:04 ` anon
2009-07-02 19:49 ` anon
2009-07-02 21:37 ` Adam Beneschan
2009-07-03 1:42 ` anon
2009-07-03 2:10 ` Adam Beneschan
2009-07-03 7:07 ` Jean-Pierre Rosen
2009-07-03 20:53 ` anon
2009-07-03 21:24 ` Georg Bauhaus
2009-07-04 9:09 ` anon
2009-07-04 13:43 ` Georg Bauhaus
2009-07-06 9:04 ` AdaMagica
2009-07-03 21:46 ` Adam Beneschan
2009-07-04 12:39 ` Martin
2009-07-01 8:09 ` Jean-Pierre Rosen
2009-07-01 15:08 ` Albrecht Käfer
2009-07-11 14:40 ` Hibou57 (Yannick Duchêne)
2009-07-11 17:18 ` sjw
2009-07-11 18:15 ` Hibou57 (Yannick Duchêne)
2009-07-11 20:20 ` anon [this message]
2009-07-12 17:57 ` Samuel Tardieu
2009-07-12 18:24 ` AdaMagica
2009-07-13 22:03 ` anon
2009-07-14 7:58 ` Martin
2009-07-16 13:54 ` anon
2009-07-16 14:41 ` Martin
2009-07-16 15:12 ` Adam Beneschan
2009-07-11 14:43 ` Hibou57 (Yannick Duchêne)
2009-07-11 15:22 ` Albrecht Käfer
2009-06-29 8:42 ` Martin
2009-06-29 8:54 ` Dmitry A. Kazakov
2009-06-29 10:10 ` Martin
2009-06-29 12:34 ` Dmitry A. Kazakov
2009-06-29 19:26 ` anon
2009-06-29 23:02 ` Martin
2009-06-29 19:47 ` anon
2009-06-30 8:31 ` Ludovic Brenta
2009-06-28 19:54 ` tmoran
2009-06-28 22:34 ` Gary Scott
2009-06-28 23:15 ` John B. Matthews
2009-06-28 23:21 ` anon
2009-06-29 7:18 ` Dmitry A. Kazakov
2009-06-29 9:52 ` Georg Bauhaus
2009-06-29 12:43 ` Dmitry A. Kazakov
2009-06-29 13:36 ` Rob Solomon
2009-06-29 14:03 ` Robert A Duff
2009-06-29 14:13 ` Georg Bauhaus
2009-06-29 14:18 ` Ludovic Brenta
2009-06-29 15:40 ` Robert A Duff
2009-07-03 1:41 ` Rob Solomon
2009-07-03 7:12 ` Learning Ada (Was: unsigned type) Jacob Sparre Andersen
2009-07-03 8:38 ` Learning Ada Peter Hermann
2009-07-03 9:44 ` Georg Bauhaus
2009-07-03 22:20 ` Learning Ada (Was: unsigned type) anon
2009-07-04 14:53 ` Georg Bauhaus
2009-07-05 23:21 ` anon
2009-07-06 0:05 ` Ludovic Brenta
2009-07-06 0:19 ` Learning Ada Albrecht Käfer
2009-07-06 2:50 ` anon
2009-07-06 6:18 ` AdaMagica
2009-07-06 7:47 ` Jean-Pierre Rosen
2009-07-06 20:21 ` anon
2009-07-06 21:08 ` Georg Bauhaus
2009-07-06 22:43 ` Frank J. Lhota
2009-07-09 22:28 ` anon
2009-07-10 6:23 ` AdaMagica
2009-07-06 10:53 ` Learning Ada (Was: unsigned type) Georg Bauhaus
2009-07-06 19:34 ` anon
2009-07-06 20:29 ` Learning Ada Albrecht Käfer
2009-07-06 21:04 ` Learning Ada (Was: unsigned type) Georg Bauhaus
2009-07-07 19:25 ` sjw
2009-07-06 23:15 ` Randy Brukardt
2009-07-07 15:29 ` Adam Beneschan
2009-07-09 0:15 ` Randy Brukardt
2009-07-09 15:26 ` Adam Beneschan
2009-06-29 15:37 ` unsigned type Adam Beneschan
2009-07-06 20:20 ` Dave
2009-06-29 16:51 ` Martin Krischik
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