array and pointers

array and pointers

[shoko]

hi
i am new in ada
my question is:
i have a function that returns unconstrained array
i am tring to create a pointer to the new array 
could somone help me:

what is wwrong in the following code?:

type Arr is Array(Item range<>) of Integer;
a:Arr:=(1,2,2,2,3,4,3) ; 
type n_array_Ptr is access Arr;
n: n_array_Ptr;

begin
     n:= new Array_filter(a); 
     
     put_line("hello");

Re: array and pointers

[Gautier Write-only]

shoko:

# what is wwrong in the following code?:
# 
# type Arr is Array(Item range<>) of Integer;
# a:Arr:=(1,2,2,2,3,4,3) ;
# type n_array_Ptr is access Arr;
# n: n_array_Ptr;
# 
# begin
#      n:= new Array_filter(a);
# 
#      put_line("hello");

A good idea is to read what the compiler says.
Here a test with GNAT:

arrrrrrr.adb:9:14: "Array_filter" is undefined

Okay, surely you meant "Arr" instead of "Array_filter".

     n:= new Arr(a); 

Let's try again:

arrrrrrr.adb:9:17: if qualified expression was meant, use apostrophe
arrrrrrr.adb:9:18: expect subtype mark for index constraint

If you want to copy a into the new n.all you have to use apostrophe

     n:= new Arr'(a); 

HTH
________________________________________________________
Gautier  --  http://www.mysunrise.ch/users/gdm/gsoft.htm

NB: For a direct answer, e-mail address on the Web site!

Re: array and pointers

[Steve]

To create a new dynamically allocated array and initialize it with the
result from Array_Filter use:

  N := new Arr'( Array_Filter( A ) );

Also, since you say you're new to Ada, I'll also mention that this is an
unusual way of doing things in Ada.  A more common approach is to use
something like:

  declare
    Filtered_Data : Arr := Array_Filter( A );
  begin
    -- Do stuff with Filtered_Data here
  end;

Which avoids dynamic allocation on the heap altogether.

Steve
(The Duck)

"shoko" <shoko2004@hotmail.com> wrote in message
news:4948f537.0311220139.570c8a4e@posting.google.com...
> hi
> i am new in ada
> my question is:
> i have a function that returns unconstrained array
> i am tring to create a pointer to the new array
> could somone help me:
>
> what is wwrong in the following code?:
>
> type Arr is Array(Item range<>) of Integer;
> a:Arr:=(1,2,2,2,3,4,3) ;
> type n_array_Ptr is access Arr;
> n: n_array_Ptr;
>
> begin
>      n:= new Array_filter(a);
>
>      put_line("hello");

Re: array and pointers

[Jeffrey Carter]

shoko wrote:
> i am new in ada
> 
> i have a function that returns unconstrained array
> i am tring to create a pointer to the new array 

Why? As an Ada beginner, you probably have no need for pointers at all, 
unless you are creating a dynamically linked data structure. Pointers 
are needed much more rarely in a high-level language such as Ada than 
they are in low-level languages such as C and its derivatives.

-- 
Jeff Carter
"Why don't you bore a hole in yourself and let the sap run out?"
Horse Feathers
49

Re: array and pointers

[Hyman Rosen]

Jeffrey Carter wrote:
> Pointers are needed much more rarely in a high-level language such as Ada
 > than they are in low-level languages such as C and its derivatives.

It happens that Ada lets you make arrays (and other things) with dynamic
sizes and C does not. I don't know that this is enough to qualify Ada as
being "high-level" and C not.