Re: Character'First, ASCII.NUL and others (Was: Re: TCP/IP Sockets with GNAT.Sockets)

[Poul-Erik Andreasen <poulerik@pea.dk>]

Adrien Plisson wrote:
> Poul-Erik Andreasen wrote:
> 
>> When i started developing job i tried with ASCII.NUL
>> things didn't work out(surely for som other reason);
>> they did when i first was using character'first.
>> (also surely for som other reason);
> 
>  >
> 
>> Are there any reason why ASCII.NUL should be better;
> 
> 
> Character'First do not describe the NUL character. i mean, it is the NUL 
> character, but you have to know the implementation details of type 
> Character to see that it's first element is the NUL character.
> 
> ASCII.NUL states explicitly that you are using the NUL character, that's 
> why its use should be better.
> 
> anyway, the package ASCII is described in ARM95 J.5, that means it is 
> part of "Obsolescent Features". as said in the ARM, "Use of these 
> features is not recommended in newly written programs.". so it is better 
> than Character'First, but there exists a better way to write this.
> 
> the better way is the use of Ada.Characters.Latin_1, which defines a 
> constant NUL describing the NUL character. unfortunately, the package 
> name is long, so you may have to write a use clause or a rename.
> 
> with Ada.Text_IO,
>     Ada.Characters.Latin_1;
> procedure Test is
>     -- see comments below
>     use Ada.Characters.Latin_1;
>     package ASCII renames Ada.Characters.Latin_1;
>     package Characters renames Ada.Characters.Latin_1;
> 
> begin
>     Ada.Text_IO.Put( Ada.Characters.Latin_1.NUL ); -- a bit long
> 
>     Ada.Text_IO.Put( NUL ); -- a bit short, NUL what ?
>                             -- NUL Character ? not sure...
> 
>     Ada.Text_IO.Put( ASCII.NUL ); -- not recommended, there is
>                                   -- a risk of confusion
> 
>     Ada.Text_IO.Put( Characters.NUL ); -- this seems better !
> end Test;
> 
> besides all this, when looking at Ada.Characters.Latin_1, we see that 
> NUL is defined this way :
> 
> NUL : constant Character := Character'Val(0);
>     
> so if you just need NUL and want to avoid declarations, you may use 
> Character'Val(0), which describes the NUL character better than 
> Character'First.
> 
point taken

thanks

Poul-Erik Andreasen