From: "Jeffrey R. Carter" <jrcarter@acm.org>
Subject: Re: Interfacing with C - pointer problem
Date: Wed, 31 Jan 2007 23:53:27 GMT
Date: 2007-01-31T23:53:27+00:00 [thread overview]
Message-ID: <XZ9wh.248687$aJ.60841@attbi_s21> (raw)
In-Reply-To: <1170267048.731810.18900@k78g2000cwa.googlegroups.com>
Adam Beneschan wrote:
>> type LPSTR is access Interfaces.C.Char;
>> procedure C_Func (x : LPSTR); -- expects an address (C-pointer, 32-bit)
>> and then
>> data : Interfaces.C.char_array := Interfaces.C.To_C("ABC");
>> and
>> C_Func (data(data'first)'unchecked_access);
>
> Or perhaps better:
>
> procedure C_Func (x : Interfaces.C.Strings.chars_ptr);
>
> data : aliased Interfaces.C.char_array := Interfaces.C.To_C
> ("ABC");
>
> C_Func (Interfaces.C.Strings.To_Chars_Ptr (data'unchecked_access));
>
> May as well use the stuff Ada provides for this exact purpose.
Right. Therefore, even better:
procedure C_Func (X : in Interfaces.C.Char_Array);
pragma Import (C, C_Func, ...);
Data : Interfaces.C.Char_Array := Interfaces.C.To_C ("ABC);
C_Func (X => Data);
The language passes this a a pointer to Data (Data'First). See ARM B.3
(70): "An Ada parameter of an array type with component type T, of any
mode, is passed as a t* argument to a C function, where t is the C type
corresponding to the Ada type T."
--
Jeff Carter
"Alms for an ex-leper!"
Monty Python's Life of Brian
75
prev parent reply other threads:[~2007-01-31 23:53 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-01-30 14:23 Interfacing with C - pointer problem Gerd
2007-01-30 15:53 ` Frank J. Lhota
2007-01-30 21:10 ` tmoran
2007-01-31 18:10 ` Adam Beneschan
2007-01-31 23:53 ` Jeffrey R. Carter [this message]
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