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From: Robert Dewar <robert_dewar@my-deja.com>
Newsgroups: comp.lang.ada
Subject: Re: Interface to C; Storage_Error
Date: Thu, 21 Dec 2000 11:38:59 GMT
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In article <VKe06.176137$U46.5519033@news1.sttls1.wa.home.com>,
  "DuckE" <nospam_steved94@home.com> wrote:
>   function GetNextVal( srv : access Srv_Handle;
>                        rslt : access Srv_Handle;
>                        ctx  : access Ctx_Handle;
>                        name : C.Char_Array;
>                        dbl  : access C.Double;
>                        flt  : access Flt_Handle ) return
>                                                      C.Int;
>   pragma Import( C, GetNextVal );

A general warning is the reminder that "access foo" is not
a generally usable translation of a pointer parameter in C,
since in the Ada case, null values would not be permitted.

> Since the "C" prototype is using "char *" I suspect you need
> to allocate the data to send to the function.

I see no reason for this suspicion, either on the basis of how
any compiler I know about works, or from the RM, please tell us
where you got this idea from :-)

> Also... beware of callbacks.  I'm not sure if GNAT behaves
> the same, but with ObjectAd if you are inside of a callback
> from a "C" library and you attempt to perform an Ada tasking
> operation (ie: Rendevous or Protected Operation) bad things
> happen.

That sounds like a significant restriction. GNAT has no such
restriction.




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