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From: "Henrik Quintel" <henrik.quintel@gmx.de>
Newsgroups: comp.lang.ada
Subject: C Interface
Date: Wed, 3 Apr 2002 13:05:05 +0200
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Date: 2002-04-03T13:05:05+02:00
List-Id: <comp.lang.ada>

Dear all,
I have a large C program and want to use the C Bindings win32ada for the
GNAT 3.13p.
I have insatlled GNAT and the Bindings in a correct way. In the standard I
have found the
following example about the C function strcpy:

-- Example of using the Interfaces.C package:
-- Calling the C Library Function strcpy
with Interfaces.C;
procedure Test is
package C renames Interfaces.C;
use type C.char_array;
-- Call <string.h>strcpy:
-- C definition of strcpy: char *strcpy(char *s1, const char *s2);
-- This function copies the string pointed to by s2 (including the
terminating null character)
-- into the array pointed to by s1. If copying takes place between objects
that overlap,
-- the behavior is undefined. The strcpy function returns the value of s1.
-- Note: since the C function's return value is of no interest, the Ada
interface is a procedure
procedure Strcpy (Target : out C.char_array;
Source : in C.char_array);
pragma Import(C, Strcpy, "strcpy");
Chars1 : C.char_array(1..20);
Chars2 : C.char_array(1..20);
begin
Chars2(1..6) := "qwert" & C.nul;
Strcpy(Chars1, Chars2);
-- Now Chars1(1..6) = "qwert" & C.Nul
end Test;

This example works very fine with my compiler. Now, I have tried to display
the contents
of Chars1 but I don't know how. I have tried several ways but no one worked.

Additional, I have several problems to understand the example above. If I
want to
interface to the function Strlen - Prototype is: function Strlen (Item : in
chars_ptr) return size_t;
what can I do get access to it. Can someone explain me a general way what to
do to interface
C functions in Ada? I have read the online help that comes along with
win32ada, but the explanation
is not so good. Does someone knows if there are examples which explain the
access to the
C interface functions. It would be very nice if someone can give me
references or examples.

Thanks for all in advance.

Yours Henrik