Re: Need some light on using Ada or not

[Brian Drummond <brian_drummond@btconnect.com>]

On 20 Feb 2011 00:20:56 GMT, "Luis P. Mendes" <luislupeXXX@gmailXXX.com> wrote:

>Sat, 19 Feb 2011 13:07:58 +0000, Brian Drummond escreveu:
> 
>> Ada can easily bind to C libraries, it's standard and well documented.

>> C++ bindings are also possible, but with some work and (currently) some
>> limitations.
>> A GCC recent enough to support "-f-dump-ada-spec" will auto-generate an
>> Ada spec from C++ sources, which will save a lot of the work. 
>
>Would you mind giving me an example?

See below...

>Please consider the following C++ code:
>===== header file
>$ cat aleatorio.h 

>===== source file
>$ cat aleatorio.cpp 

>=====
>
>From Ada, how can I use these h and cpp files to call, for example, 
>gerarAleatorioInteiro(0,10)?

Here is what I did.

1)  Comment out the #includes in aleatorio.h.
They are unused; enlarge the namespace; and are repeated in the .cpp file
anyway.

Save it as aleatorio.hpp. (This forces C++-style Ada specs rather than C-style,
which is essential to link to C++ code)

2) Generate the specs automatically.
/usr/gnat/bin/gcc -fdump-ada-spec aleatorio.hpp
produces an automatic spec file
aleatorio_hpp.ads
-------------------------------
with Interfaces.C; use Interfaces.C;

package aleatorio_hpp is

   procedure iniciarSemente;  -- aleatorio.hpp:8:21
   pragma Import (CPP, iniciarSemente, "_Z14iniciarSementev");

   function gerarAleatorio (a : int; b : int) return double;  
	-- aleatorio.hpp:9:35
   pragma Import (CPP, gerarAleatorio, "_Z14gerarAleatorioii");

   function gerarAleatorioInteiro (a : int; b : int) return int;  
	-- aleatorio.hpp:10:39
   pragma Import (CPP, gerarAleatorioInteiro, "_Z21gerarAleatorioInteiroii");

   function arredondar (res : double) return int;  
	-- aleatorio.hpp:11:26
   pragma Import (CPP, arredondar, "_Z10arredondard");

end aleatorio_hpp;
-------------------------------

3) Not essential but recommended ...

Write a wrapper package to hide the C interface and C types, and to make the
interface look like Ada: random_wrapper.ads, random_wrapper.adb.
(This constitutes a "thick binding", while package aleatorio_h is a "thin
binding")
At this point you can choose what to expose to the Ada code; 
I have been selective (or lazy!)

------------ random_wrapper.ads --------------
package random_wrapper is
 
   procedure initialise_seed;
   function random_between(a,b : in Integer) return Integer;
  
end random_wrapper;
------------ random_wrapper.adb --------------
with aleatorio_hpp;		
use aleatorio_hpp;
with Interfaces.C; 
use Interfaces.C;

package body random_wrapper is

   procedure initialise_seed is
   begin
      iniciarSemente;
   end initialise_seed;

   function random_between(a,b : in Integer) return Integer is
   begin
      return Integer(gerarAleatorioInteiro (int(a), int(b)));
   end random_between;

end random_wrapper;
----------------------------------------------

4)  Write your Ada program...
------------ random.adb ----------------------
--Random number tester

with Ada.Text_Io; 		use Ada.Text_Io;
with Ada.Integer_Text_Io; 	use Ada.Integer_Text_Io;
with random_wrapper;		use random_wrapper;

procedure random is

begin
   initialise_seed;
   Put("Five random numbers");
   New_Line;
   for i in 1 .. 5 loop
      Put(random_between(1,100));
      New_Line;
   end loop;
end random;
----------------------------------------------

5) Compile the C++ portion (more complex examples may need a Makefile)

g++ -g -m64 -c -o aleatorio.o aleatorio.cpp 

6) Build the Ada portion. 

gnatmake -m64 -gnat05 -gnato -gnatwa -fstack-check -o random random.adb \
	-largs ./aleatorio.o -lstdc++ 

Note additional arguments "-largs ./aleatorio.o -lstdc++" to gnatlink; 
extend these if you add more C++ objects and libraries. 

7) 
Run it.

./random
Five random numbers
          9
         40
          2
         77
         66