Re: Unbounded string deallocation

[Marin David Condic <condicma@bogon.pwfl.com>]

Matthew Heaney wrote:

> >   -- grab approx 1024 bytes of memory
> >   my_string := new ada.strings.unbounded_string.To_Unbound_String(1024);
> >
> >   -- give back the 1024 bytes and grab 2048 new memory bytes
> >   my_string := new ada.strings.unbounded_string.To_Unbound_String(2048);
> >
> > end
> >
> > Is this correct?
>
> No, it is completely incorrect:
>
> o  Do NOT use the allocator new.  Any allocation is done implicitly, as part
> of the call to To_Unbounded_String.
>
> o  To_Unbounded_String takes type String as an argument; it does NOT take an
> integer type.
>

In fairness, the package Ada.Strings.Unbounded does provide a To_Unbounded_String
which will take a length as a parameter. It also provides an access type for the
Fixed Strings. The example above is incorrect because it is mixing String_Access
types with Unbounded_String types, but with a little adjustment, one could have
done the dynamic allocation and used the Free procedure for deallocation - although
I can't for the life of me think of why anyone would want to if nobody was standing
over them with a stick forcing them to.

IMHO, the To_Unbounded_String and To_String are just about all you need for most
applications. And if Text_IO and some other basic things had Unbounded_String
alternatives, you wouldn't even need these calls. I suppose there might be
applications with efficiency issues, but for most things Unbounded_String is quite
adequate.

>
> Here's what you do:
>
>   declare
>     My_String : Unbounded_String;
>   begin
>     My_String := To_Unbounded_String ("this is a string");
>     -- all allocation is implicit
>
>     My_String := To_Unbounded_String ("this is another string");
>     -- all deallocation is implicit
>     -- all allocation is implicit
>
>     My_String := To_Unbounded_String ("this is yet another string");
>     -- all deallocation is implicit
>     -- all allocation is implicit
>   end;
>   -- all deallocation is implicit

A very clear example. I think that C programmers coming over to Ada have a tendency
to want to grab pointers to everything or null-terminate strings unnecessarily just
because that is what they are used to doing. Eventually, they get used to "The Ada
Way". :-)

MDC
--
Marin David Condic
Real Time & Embedded Systems, Propulsion Systems Analysis
United Technologies, Pratt & Whitney, Large Military Engines
M/S 731-95, P.O.B. 109600, West Palm Beach, FL, 33410-9600
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