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Date: 29 Apr 92 13:55:31 GMT
From: psinntp!vitro.com!v7.vitro.com!vaxs09@uunet.uu.net
Subject: Re: Oh, no! Ada-strings...
Message-ID: <1992Apr29.085531.159@v7.vitro.com>
List-Id: <comp.lang.ada>

>toron@CCUCVX.UNICAN.ES (Borja TORON ANTONS) writes:
> The solution is to use 'variable strings' as follows:
>
> Package Var_string is
>    type vstring(len: natural:=200) is record
>           str : STRING (1..len);
>    end record;

*heavy sigh*

Most of the time, this won't work.

You are declaring an unconstrained type that can take an amount of storage
between 1 and integer'last (approximately).  The compiler has two reasonable
choices in dealing with objects of this type.

1.  Preallocate the maximum space needed by any object of that type.

2.  Allocate the current size for the object. Re-allocate when the space
    requirement changes.

The tradeoff here is one of speed (1 chews less CPU) against space (2 chews
less memory).  By default, my compiler (VAX Ada) and many others will
choose option 1, pre-allocating your "variable" strings.  In my case,
that's 2 gigabytes of storage for one string.  At run time, an attempt
to allocate a vstring produces a constraint error.

	John Briggs			vaxs09@v7.vitro.com