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From: Lutz Donnerhacke <lutz@iks-jena.de>
Newsgroups: comp.lang.ada
Subject: Re: [Spark] Arrays of Strings
Date: Wed, 9 Apr 2003 08:10:06 +0000 (UTC)
Organization: IKS GmbH Jena
Message-ID: <slrnb97lat.or.lutz@taranis.iks-jena.de>
References: <slrnb95ehu.ob.lutz@taranis.iks-jena.de>
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* Eric G. Miller wrote:
> In <slrnb95ehu.ob.lutz@taranis.iks-jena.de>, Lutz Donnerhacke wrote:
> 
>> In order to implement thin an execve binding, I wonder how to emulate the
>> C-Type "char const * const x []". Any bright ideas?
> 
> Errm, my local definition of execve looks like:
> 
> int execve(const char *filename, 
>            char *const argv [], char *const envp[]);
> 
> What'd the const pointer be for?  Even if your definition had such, that'd
> be a burden upon the C function, but shouldn't much affect the Ada side of
> things.

"char const * const []" is an array of constant pointers to constant chars.
The modifier const is a postfix modifier. For the first element an
equivalent prefix notation exists for syntactic shugar.

> Try the following out (rename "/tmp/hello" as appropriate)...
> 
> with Ada.Text_Io;
> with Interfaces.C.Strings;

The use of this packages is not possible in Spark. I need an emulation or
shadow of the package Interfaces.C.Strings.

> use Ada.Text_Io;

"use package" is not allowed in Spark.

>    Argv : C.Strings.Chars_Ptr_Array :=
>      (C.Strings.New_String("John"),
>       C.Strings.New_String("Bill"),
>       C.Strings.New_String("Bob"),
>       C.Strings.Null_Ptr);

This involves dynamic memory, which should be avioded as much as possible in
Spark. Language based dynamic memory management is not supported in Spark.

I hope it's clear, what I expect:

package Interfaces is
end Interfaces;

package Interfaces.C is
   type int is range Integer'First .. Integer'Last; -- has to be correct.
end Interfaces.C;

package Interfaces.C.Strings is
   type Chars_Ptr is private;
   type Chars_Ptr_Array is array (Positive range <>) of Chars_Ptr;
private
   type Chars_Ptr is mod 2**32; -- has to be correct.
end Interfaces.C.Strings;


with Interfaces.C.Strings;
--# inherit Interfaces.C.Strings, Interfaces.C;

package Executor is                                                           
   function Execve (
     Filename : Interfaces.C.Strings.Chars_Ptr;
     Argv     : Interfaces.C.Strings.Chars_Ptr_Array;
     Envp     : Interfaces.C.Strings.Chars_Ptr_Array)
     return Interfaces.C.Int;
   
   pragma Import (Convention => C,                                            
     Entity => Execve,                                           
     External_Name => "execve");                                 
end Executor;