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digitalmars.D.learn - conversion error related to array index

reply thorstein <torsten.lange mail.de> writes:
Hi,

I get the following compile error with this function below:
source\mod_data\matrices.d(66,12): Error: cannot implicitly 
convert expression (j) of type ulong to uint

(66,12) is [j] in row[j]

Using uint as type for rows, cols (i.e. the indices) works. Is 
ulong not allowed for array indices? I could not find the 
respective information.

Thanks!


49	private double[][] matrix_uniform(ulong rows, ulong cols, 
double lbound, double ubound, ulong precision)
50	{
51	  double[][] array;
52	  double[] rowT;
53	  auto gen = Random(unpredictableSeed);
54	  auto rndUniform = uniform(lbound, ubound, gen);
55	
56	  foreach(ulong i; 0..cols)
57	  {
58	    rowT ~= 0;
59	  }
60	
61	  foreach(ulong i; 0..rows)
62	  {
63	    foreach(ulong j; 0..cols)
64	    {
65	      rndUniform = uniform(lbound, ubound, gen);
66	      rowT[j] = to!double(rndUniform) / 10^^precision;
67	    }
68	    array ~= rowT.dup;
69	  }
70	    return array;
71	}
Oct 04
parent Jonathan M Davis <newsgroup.d jmdavisprog.com> writes:
On Wednesday, October 04, 2017 09:04:10 thorstein via Digitalmars-d-learn 
wrote:
 Hi,

 I get the following compile error with this function below:
 source\mod_data\matrices.d(66,12): Error: cannot implicitly
 convert expression (j) of type ulong to uint

 (66,12) is [j] in row[j]

 Using uint as type for rows, cols (i.e. the indices) works. Is
 ulong not allowed for array indices? I could not find the
 respective information.
Array indices - and array length - are size_t. If you're on a 32-bit system, that's an alias to uint, whereas on a 64-bit system, it's an alias to ulong. In general, code should be using size_t when dealing with arrays not uint or ulong (unless you're talking about having elements of uint or ulong). If you don't use size_t, then you're likely to run into problems when compiling for a different architecture. But if you have a ulong that you need to convert to a uint, then you can always cast or use std.conv.to!uint so long as the number will actually fit in a uint. - Jonathan M Davis
Oct 04