Arrays & pointers question

Arrays & pointers question

[csaagpDIESPAMDIE]

Not used to pointers & Ada so I'd appreciate some help.

I have a simple sort routine that sorts an array of integers.
I have several variables of the same array type, so I'd like to pass in
the address of each array to the sort routine.

if my type/variable declarations are as such:

  type MYTYPE is array (1 .. 10) of INTEGER;
  X1: MYTYPE;
  X2: MYTYPE;
  X3: MYTYPE;

 I have a SORT procedure that takes 2 parameters: the first is the
number of entries,
and the 2nd is the address of the array.

What's the correct syntax for the procedure declaration, the procedure
call, and the references to the array elements inside the procedure?

thanks.

Re: Arrays & pointers question

[tmoran]

>   type MYTYPE is array (1 .. 10) of INTEGER;
>   X1: MYTYPE;
>   X2: MYTYPE;
>   X3: MYTYPE;
>
>  I have a SORT procedure that takes 2 parameters: the first is the
> number of entries,
> and the 2nd is the address of the array.
>
> What's the correct syntax for the procedure declaration, the procedure
> call, and the references to the array elements inside the procedure?

    Arrays in Ada are not pointers or addresses but rather objects, so
you need to pass the object in, sort it, and pass it out (don't worry,
the compiler is smart enough to generate code that passes references even
though logically it's copying the array).

    Also, arrays carry their own upper and lower boundaries, so you
don't need to pass a count.

So declare your procedure this way:
  procedure Sort(This_Array : in out MyType) is
  begin
    for i in This_Array'range loop
      for j in This_Array'first .. i-1 loop
        if This_Array(i) < This_Array(j) then ....
  ...
and call it like this:
  Sort(X1);

Note that in this case you've declared any array of type MyType to have
exactly 10 elements, so the compiler doesn't even need to pass the count,
and it can generate code knowing that This_Array'range is 1 ..  10 and
This_Array'first is 1.

If you want to sort different length arrays, try

    type MYTYPE is array (Integer range <>) of INTEGER;
    X1: MYTYPE(1 .. 10);
    X2: MYTYPE(1 .. 20000);

The declaration and call of Sort are unchanged.  Since the parameter to
Sort has bounds specified at run time, you also have the option of
sorting just a slice of a MYTYPE array, eg the first ten elements of X2:
   Sort(X2(1 .. 10));
or the last ten elements:
   Sort(X2(19991 .. 20000));

Re: Arrays & pointers question

[csaagpDIESPAMDIE]

Thanks, that worked great.

After several tries I was able to cobble together a version that used
access type & 'aliased' etc but your solution reads much cleaner.  Plus
I didn't know the compiler handled the generated code efficiently.

My 1..10 example was just for simplicity - I have different # entries
in each array so I need a count.

Re: Arrays & pointers question

[Marc A. Criley]

csaagpDIESPAMDIE@yahoo.com wrote:

> My 1..10 example was just for simplicity - I have different # entries
> in each array so I need a count.

But as you saw in Tom's example, you don't.  I hope you understood how 
'Range works as he illustrated.  It's a very powerful thing to know.

-- Marc A. Criley
-- McKae Technologies
-- www.mckae.com
-- DTraq - XPath In Ada - XML EZ Out

Re: Arrays & pointers question

[csaagpDIESPAMDIE]

All objects of my array type have the same dimensions; not all objects
fill out the same items.
All of my array objects have the same 'first value, the same 'last
value and the same 'range,
but they all do not fill out their arrays to the 'last value.

Re: Arrays & pointers question

[Marc A. Criley]

csaagpDIESPAMDIE@yahoo.com wrote:
> All objects of my array type have the same dimensions; not all objects
> fill out the same items.
> All of my array objects have the same 'first value, the same 'last
> value and the same 'range,
> but they all do not fill out their arrays to the 'last value.
> 

That's why Tom also mentioned slicing the array that you pass to your 
function:

Given:
    X2: MYTYPE(1 .. 20000);

<quote>
The declaration and call of Sort are unchanged.  Since the parameter to
Sort has bounds specified at run time, you also have the option of
sorting just a slice of a MYTYPE array, eg the first ten elements of X2:
    Sort(X2(1 .. 10));
or the last ten elements:
    Sort(X2(19991 .. 20000));
</quote>

Using 'Range in the Sort function properly handles both of these cases 
(and any other slices you need to use).  Take a look at the latter part 
of his posting again to see how this works.

-- Marc A. Criley
-- McKae Technologies
-- www.mckae.com
-- DTraq - XPath In Ada - XML EZ Out

Re: Arrays & pointers question

[csaagpDIESPAMDIE]

Gotcha, thanks for that.