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Date: 9 Nov 91 03:20:55 GMT
From: eachus@mitre-bedford.arpa  (Robert I. Eachus)
Subject: Re: Is this legal ?
Message-ID: <EACHUS.91Nov8192055@Dr_No.mitre.org>
List-Id: <comp.lang.ada>

In article <1991Nov08.205832.26958@convex.com> pelakh@convex.com (Boris Pelakh)
 writes:

   The following procedure produces a warning at compile time saying that
   the declaration of NULL_LINE is exceeding the storage limit of the 
   implementation. At runtime, I get a storage error. It looks like the 
   unconstrined declare is causing an attempt to allocate a STRING(1..MAX_INT),
   even though I would expect it to only declare a STRING(1..10). The RM
   does not explain this particular case. Any ideas ?

   Why would you expect it to allocate space for only 10 characters?
The object NULL_LINE can be used to store a STRING value of any size,
since the discriminant has a default and is of type INTEGER.  There
are two standard implementations of such records, the `hidden pointer'
version which stores the actual values on the heap, and an allocate
the maximum strategy.  (Some compilers implement both, with a size at
which they cut over.)

   If you want to store reasonable length lines in a portable way,
try:

   procedure NOT_BROKE is
      subtype LINE_LENGTH is INTEGER range 0..1024;
      type VAR_LINE(LENGTH : LINE_LENGTH := 10) is
	 record
		IMAGE : STRING(1..LENGTH);
	 end record;
      NULL_LINE : VAR_LINE;
   begin
       null;
   end BROKE;

--

					Robert I. Eachus

with STANDARD_DISCLAIMER;
use  STANDARD_DISCLAIMER;
function MESSAGE (TEXT: in CLEVER_IDEAS) return BETTER_IDEAS is...