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From: nickroberts@ukf.net (Nick Roberts)
Newsgroups: comp.lang.ada
Subject: Re: How to find directory where the program is?
Date: Sat, 27 Apr 2002 21:12:24 GMT
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On 27 Apr 2002 09:39:03 -0500, Kilgallen@SpamCop.net (Larry Kilgallen)
strongly typed:

>In article <aabjie$pru$1@nh.pace.co.uk>, "Marin David Condic" <dont.bother.mcondic.auntie.spam@[acm.org> writes:
>
>> Most OS's have some means for keeping that kind of thing around somewhere,
>> just that it isn't going to be a "portable" answer. Its the sort of thing
>> that Ada has been very good at hiding in the past - maybe that's something
>> that needs to be in an OS Interface package?
>
>But sometimes there will not be an answer, if you are expecting a
>disk location.  On VMS the program you are running might be on
>magnetic tape.

I think we might consider that a bit of a pathological case, nowadays,
Larry!

Besides, I think Marin was suggesting a standard way to obtain
configuration data (not necessarily anything to do with where the
executable is located).

May I propose:

   with Ada.IO_Exceptions;
   package Ada.Program_Environment is

      type Mechanism is (...);
      -- implementation defined enumeration type

      Default_Mechanism: Mechanism := ...;
      -- may be initialised statically or dynamically

      function Get_Item (Name: in Wide_String;
                         Via:  in Mechanism := Default_Mechanism)
         return Wide_String;
      -- returns "" if item not found

      procedure Set_Item (Name, Value: in Wide_String;
                          Via:         in Mechanism := Default_Mechanism);
      -- may or may not delete if Value=""

      procedure Delete_Item (Name: in Wide_String;
                             Via:  in Mechanism := Default_Mechanism);
      -- deletes or (if cannot) sets to ""

      Name_Error:   exception renames Ada.IO_Exceptions.Name_Error;
      Use_Error:    exception renames Ada.IO_Exceptions.Use_Error;
      Device_Error: exception renames Ada.IO_Exceptions.Device_Error;

   end Ada.Program_Environment;

The different mechanisms for Windows (32-bit) might be:

   ( Environment_Variables,
     Windows_INI_File,
     Program_Home_INI_File,
     Registry_User,
     Registry_Local,
     Registry_System );

Just a thought.

PS: The syntax of names is intended to be left implementation-defined (just
like file names). However, it might be necessary to single out one
punctuation character that must be usable (as a delimiter) with impunity.
Perhaps '.' would be best for this. PPS: '=' is likely to be unusable.

-- 
Nick Roberts