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From: jerry@jvdsys.nextjk.stuyts.nl (Jerry van Dijk)
Subject: Re: Need help re: System Calls
Date: 1997/04/08
Message-ID: <860461839.15snx@jvdsys.nextjk.stuyts.nl>#1/1
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Distribution: world
References: <Pine.SGI.3.94.970406210904.4241A-100000@sandcast
Organization: *JerryWare HQ*, Haarlem, Holland
Newsgroups: comp.lang.ada
Date: 1997-04-08T00:00:00+00:00
List-Id: <comp.lang.ada>


>I am looking for information about how to perform system calls (in this
>case, UNIX commands) in the GNAT compiler of Ada 95. Any help would be
>appreciated. (Note: in this case, I am trying to implement a command which
>is stored in a string).

Usually unix has a C library function to execute another program, for
example:

   int system (constant char *command)

using GNAT, simply import this library function and call it directly,
using the standard C interface as defined in Appendix B.3.

In this case you can take advantage of the fact that for GNAT
Interfaces.C.int equals Integer. But, as you also need to convert the
Ada string into a C-type zero terminated ascii character array, it is
probably useful to put a wrapper around the C library call:

   with Interfaces.C;

   procedure Demo is

      function Call_System (Command : String) return Integer is
         function system (Command : Interfaces.C.char_array) return Integer;
         pragma Import (C, system);
      begin
         return system (Interfaces.C.To_C (Command));
      end Call_System;

      Result : Integer;

   begin
      Result := Call_System ("ls");
   end Demo;

Note that importing 'system' as a C function automatically takes care
of calling the function with a pointer to the character array.

--

-- Jerry van Dijk       | Haarlem, Holland
-- Business Consultant  | Team Ada
-- Ordina Finance       | jdijk@acm.org