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March 26, 2005
3D Arrays - Non-block Arrays possible?
I still do not fully understand how arrays in D really work. And that is 
becoming apparent with 3D arrays. I hope someone can help me better 
understand them and how to manipulate them.

E.g. char[3][5][] would be a 3x5 array, a 3x5 block no matter if element
char[0] ever requires [5] elements or not. This is the way I used to 
handle 3D arrays in C.

But in D I am starting to wonder if

  char[][][] d;

a dynamic array, would let me define

  char[0][5][]
  char[1][2][]
  char[2][3][]

meaning to be able to define how many elements char[0] will have (5), 
then a different number (2) for char[1] etc. Without having memory 
wasted by empty elements?

If this is possible how would one define them?

  char[][][] d;
  d.length = 3;
  d[0].length = 5;
  d[1].length = 2;
  d[2].length = 3;

Would that work?

AEon
March 26, 2005
Re: 3D Arrays - Non-block Arrays possible?
On Sun, 27 Mar 2005 00:22:08 +0100, AEon wrote:

> I still do not fully understand how arrays in D really work. And that is 
> becoming apparent with 3D arrays. I hope someone can help me better 
> understand them and how to manipulate them.
> 
> E.g. char[3][5][] would be a 3x5 array, a 3x5 block no matter if element
> char[0] ever requires [5] elements or not. This is the way I used to 
> handle 3D arrays in C.
> 
> But in D I am starting to wonder if
> 
>    char[][][] d;
> 
> a dynamic array, would let me define
> 
>    char[0][5][]
>    char[1][2][]
>    char[2][3][]
> 
> meaning to be able to define how many elements char[0] will have (5), 
> then a different number (2) for char[1] etc. Without having memory 
> wasted by empty elements?
> 
> If this is possible how would one define them?
> 
>    char[][][] d;
>    d.length = 3;
>    d[0].length = 5;
>    d[1].length = 2;
>    d[2].length = 3;
> 
> Would that work?

Yes. Another way of looking at this is ...

alias char[] Line;
alias Line[] Page;
alias Page[] Chapter;

void main()
{
   Chapter d;
   d.length = 3; // This chapter has three pages.
   d[0].length = 6; // 1st page has 6 lines
   d[1].length = 7; // 2nd page has 7 lines
   d[2].length = 8; // 3rd page has 8 lines;


   d[0][0] = "Once upon a time, in land far, far, away";
   d[0][1] = "there lived a crooked little man, named";
   d[0][2] = "'Xyzzy'. One day he decided to clean up";
   d[0][3] = "his cave. You see, he lived in a colossal";
   d[0][4] = "cave, deep underground, with his two";
   d[0][5] = "pets; a dwarf and a unicorn.";
   
   d[1][0] = "... etc ... etc ... etc ";    
}

-- 
Derek Parnell
Melbourne, Australia
27/03/2005 9:57:29 AM
March 27, 2005
Re: 3D Arrays - Non-block Arrays possible?
Derek Parnell wrote:

> On Sun, 27 Mar 2005 00:22:08 +0100, AEon wrote:
> 
>>I still do not fully understand how arrays in D really work. And that is 
>>becoming apparent with 3D arrays. I hope someone can help me better 
>>understand them and how to manipulate them.
>>
>>E.g. char[3][5][] would be a 3x5 array, a 3x5 block no matter if element
>>char[0] ever requires [5] elements or not. This is the way I used to 
>>handle 3D arrays in C.
>>
>>But in D I am starting to wonder if
>>
>>   char[][][] d;
>>
>>a dynamic array, would let me define
>>
>>   char[0][5][]
>>   char[1][2][]
>>   char[2][3][]
>>
>>meaning to be able to define how many elements char[0] will have (5), 
>>then a different number (2) for char[1] etc. Without having memory 
>>wasted by empty elements?
>>
>>If this is possible how would one define them?
>>
>>   char[][][] d;
>>   d.length = 3;
>>   d[0].length = 5;
>>   d[1].length = 2;
>>   d[2].length = 3;
>>
>>Would that work?
> 
> 
> Yes. Another way of looking at this is ...
> 
> alias char[] Line;
> alias Line[] Page;
> alias Page[] Chapter;
> 
> void main()
> {
>     Chapter d;
>     d.length = 3; // This chapter has three pages.
>     d[0].length = 6; // 1st page has 6 lines
>     d[1].length = 7; // 2nd page has 7 lines
>     d[2].length = 8; // 3rd page has 8 lines;
> 
> 
>     d[0][0] = "Once upon a time, in land far, far, away";
>     d[0][1] = "there lived a crooked little man, named";
>     d[0][2] = "'Xyzzy'. One day he decided to clean up";
>     d[0][3] = "his cave. You see, he lived in a colossal";
>     d[0][4] = "cave, deep underground, with his two";
>     d[0][5] = "pets; a dwarf and a unicorn.";
>     
>     d[1][0] = "... etc ... etc ... etc ";    
> }

Thanx for the nix example, will try that.

Since I no longer have to use 3D blocks, this would *massively* reduce 
the amount of memory some of my temp stats calculations require, where 
(my guess) something like 90%+ of the arrays is never actually used.

And another good reason to use D :)

AEon
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