Re: basic basic ada question

[Robert A Duff <bobduff@shell01.TheWorld.com>]

"Jeffrey R. Carter" <spam.not.jrcarter@acm.not.spam.org> writes:

> markww wrote:
>> Ok, am I understanding this correctly - if I just '#include" the
>> command line package:
>
> "with" is significantly different from simple text inclusion.

True, but they serve roughly the same purpose, in practise.  For someone
coming from the C world, it's not so bad to think that a package spec is
a cleaner way to do .h files, and "with" is a cleaner way to do
#include.

>...Most of
> what you know from C/++ is wrong for Ada. The sooner you can stop
> thinking in C/++ and start thinking in Ada, the easier you will find it.

Why should one think in C or Ada?  There are lots of concepts that
transcend the languages.  After all, both languages have subroutines,
parameter passing, stack/heap allocation, etc, etc.

>>     with Ada.Command_Line; use Ada.Command_Line;
>
> As a beginner, I would strongly recommend that you avoid "use", at least
> until you understand Ada's visibility rules better.

Probably a good idea.

>> then the package defines the functions:
>>     function Argument_Count return Natural;
>>     function Argument (Number : in Positive) return String;
>> for me which I can use from then on?
>> So in my little app I can just use them like:
>>     Number_Of_Elements := Argument(0);
>> (assuming the 0th argument is the # of elements to allocate...)
>
> As you quoted, Argument's parameter Number has subtype Positive. Zero is
> not a value of Positive. So such a call will raise Constraint_Error. In
> Ada, as in life, we usually count or number things starting from
> 1. Getting away from the low-level, offset-oriented C mindset is part of
> learning to think in Ada.

Well, actually, the first argument is numbered 1 in C, too.  ;-)
argv[0] is what Ada calls Command_Name -- not one of the arguments.

Dijkstra wrote an interesting paper called "Why numbering should start
at zero", which you can find via google.  I don't buy it -- I like to
number most things starting at 1, despite his fairly reasonable
arguments to the contrary.

It's interesting that for enumeration types, T'Pos starts numbering
at 0.

- Bob