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digitalmars.D.learn - 3D Arrays - Non-block Arrays possible?

reply AEon <aeon2001 lycos.de> writes:
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
Mar 26 2005
parent reply Derek Parnell <derek psych.ward> writes:
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
Mar 26 2005
parent AEon <aeon2001 lycos.de> writes:
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
Mar 26 2005