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Date: 20 Sep 91 18:58:18 GMT
From: cis.ohio-state.edu!zaphod.mps.ohio-state.edu!uakari.primate.wisc.edu!usen
et.coe.montana.edu!milton!mfeldman@ucbvax.Berkeley.EDU  (Michael Feldman)
Subject: Re: <None>
Message-ID: <1991Sep20.185818.3721@milton.u.washington.edu>
List-Id: <comp.lang.ada>

In article <1991Sep19.165920.1820@dayton.saic.com> hopperj@dayton.saic.com writ
es:
>
>Type PRI_Stagger_Array is Array (Short_Integer Range <> ) of Short_Integer;
>
>Type InterceptReport is
>Record
>  ....
>  EXT_Length : Short_Integer;
>  PRI_Per_Stagger : PRI_Stagger_Array(EXT_Length);
>End Record;
>
>This will not compile.  Is there some why to handle a variable size message
>in Ada?

Your best bet is to use a variant record, using Ext_Length as the
discriminant. In order to let the record length vary, you'll have to
give the discriminant a default value so the type can be unconstrained.

Do you really think your message may be Short_Integer'Last elements long?
(If Short_Integer is 16 bits in your compiler, this is 32767, kind of
a long message).

If not, use a subtype indicating the realistic maximum length, because
some compilers allocate enough space to hold the maximum-length array
This is a time/space tradeoff: some compilers prefer to reallocate,
which saves space but costs time, others allocate for the maximum,
which saves time but may cost a LOT of space if the type of your
discriminant isn't realistic.

Try these type defs:

Type PRI_Stagger_Array is Array (Short_Integer Range <> ) of Short_Integer;

Type InterceptReport (EXT_Length: Short_Integer := 8) is
Record
  ....
  -- EXT_Length : Short_Integer;
  -- remove the field here; the discriminant itself is a field
  PRI_Per_Stagger : PRI_Stagger_Array(EXT_Length);
End Record;

then, once EXT_Length has a value, stored in a variable Lgth, say,
you can declare

declare
  This_Record: Intercept_Report(Ext_Length => Lgth);
begin
  ...
end;

Give this a shot - see if it works.

Mike Feldman

-------------------------------------------------------------------------------
Michael B. Feldman
Visiting Professor 1991-92               Professor
Dept. of Comp. Sci. and Engrg.           Dept. of Elect. Engrg. and Comp. Sci.
University of Washington FR-35           The George Washington University
Seattle, WA 98105                        Washington, DC 20052
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