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digitalmars.D.learn - setting array dimensions at runtime

reply user domain.invalid writes:
Hello,

I've been wondering what the easiest way is to set
the dimension of an array during runtime.

You can't write

    byte[][] a = new byte[size][size];

because the compiler will give an error. The only
thing I've been able to think of is

    byte[][] a;
    a.length = size;
    for (int i; i < size; i++) {
         a[i].length = size;
    }

But it's slower (and less convenient) than
writing

    byte[][] a = new byte[9][9];
Dec 05 2010
next sibling parent reply Matthias Walter <xammy xammy.homelinux.net> writes:
 The only thing I've been able to think of is

    byte[][] a;
    a.length = size;
    for (int i; i < size; i++) {
         a[i].length = size;
    }

auto a = new byte[][size]; foreach (ref row; a) row = new byte[size]; Matthias
Dec 05 2010
parent user domain.invalid writes:
On 5-12-2010 19:20, Matthias Walter wrote:
 The only thing I've been able to think of is

     byte[][] a;
     a.length = size;
     for (int i; i<  size; i++) {
          a[i].length = size;
     }

auto a = new byte[][size]; foreach (ref row; a) row = new byte[size];

That works. So I can write byte[] a = new byte[size]; and byte[][] a = new byte[][size]; but not byte[][] a = new byte[size][]; or byte[][] a = new byte[size][size]; let alone byte[size][size] a; BTW, somebody on stackoverflow just posted an alternative that comes closest to what I was looking for. byte[][] a = new byte[][](size, size); I saw this notation before but I can't remember where. Hey, I love D but it can be pretty confusing sometimes :) Thanks
Dec 05 2010
prev sibling next sibling parent Nekuromento <max.klyga gmail.com> writes:
On 2010-12-05 19:41:50 +0200, user domain.invalid said:

 Hello,
 
 I've been wondering what the easiest way is to set
 the dimension of an array during runtime.
 
 You can't write
 
     byte[][] a = new byte[size][size];
 
 because the compiler will give an error. The only
 thing I've been able to think of is
 
     byte[][] a;
     a.length = size;
     for (int i; i < size; i++) {
          a[i].length = size;
     }
 
 But it's slower (and less convenient) than
 writing
 
     byte[][] a = new byte[9][9];

The syntax might seem a bit misleading, but you can create multidimentional arrays like this:     int[][] foo = new int[][](5,10);     foo[4][9] = 31337; this also works for single-dimention arrays (e.g int[] foo = new int[](size);)
Dec 05 2010
prev sibling parent Jonathan M Davis <jmdavisProg gmx.com> writes:
On Sunday 05 December 2010 09:41:50 user domain.invalid wrote:
 Hello,
 
 I've been wondering what the easiest way is to set
 the dimension of an array during runtime.
 
 You can't write
 
     byte[][] a = new byte[size][size];
 
 because the compiler will give an error. The only
 thing I've been able to think of is
 
     byte[][] a;
     a.length = size;
     for (int i; i < size; i++) {
          a[i].length = size;
     }
 
 But it's slower (and less convenient) than
 writing
 
     byte[][] a = new byte[9][9];

auto a = new byte[][](9, 9); is the way to do it. Otherwise, I believe that you're trying to create a dynamic array of static arrays or somesuch. I'm not sure exactly what the problem is. However, if you just always put the array size in the parens rather than in the brackets when creating an array, then it works correctly. Setting the length in a loop like that (or creating inner arrays with new) is best when you want the inner arrays to be of different length. But when you want them to be the same length, then putting the sizes in the parens in the correct way to go. - Jonathan M Davis
Dec 05 2010