Re: How to exit an Ada program with (unix shell) error code?

[stefan-lucks@see-the.signature]

On Mon, 4 May 2009, Ludovic Brenta wrote:

> reinkor wrote on comp.lang.ada:
> > Thanks, but how I terminate the program in a "natural" way
> > (without using goto or "raise exception") ?
> 
> Simply allow the execution to reach the "end;" of the main subprogram.
> 
> with Ada.Command_Line;
> procedure Exit_With_False is
> begin
>    Ada.Command_Line.Set_Exit_Status (1); -- False, in shell terms

     Ada.Command_Line.Set_Exit_Status (Ada.Command_Line.Failure);

> end Exit_With_False; -- nothing else required

I believe, it is preferable to use the predefined constants "Success" and 
"Failure" in Ada.Command line:

  1. If you port your program to another (i.e. non-unix) system, 
     it is not clear that "1" maintains the logical value "False". 
     (Perhaps the RM is clear about that -- I didn't check ...) 

  2. Without the comment "-- False, in shell terms", many readers 
     (except for unix-shell experts, of course) would rather expect 

       Ada.Command_Line.Set_Exit_Status (1);

     to indicate a positive result ("True"), rather then "False". 

Here is a slightly larger example:

with Ada.Command_Line;
procedure False_If_No_Arguments is
   package ACL renames Ada.Command_Line;
begin
   if ACL.Argument_Count > 0 then
      ACL.Set_Exit_Status (ACL.Success);
   else
      ACL.Set_Exit_Status (ACL.Failure);
   end if;
end False_If_No_Arguments;

P.S.: (As you see, you can indicate either a positive or a negative 
outcome without ever having to raise an exception ...)



-- 
------ Stefan Lucks   --  Bauhaus-University Weimar  --   Germany  ------
               Stefan dot Lucks at uni minus weimar dot de
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