On Monday, 4 February 2013 at 15:23:20 UTC, Sparsh Mittal wrote:
I am allocating 2d array as:
double[gridSize][gridSize] gridInfo;
which works for small dimension, but for large dimension, 16Mb
limit comes.
Would you please tell me how do allocate a large 2d array
(which has to be done as a dynamic array)? It is a square grid
and dimensions are already known.
I also searched internet but could not find an answer. Thanks.
If all (but last of) the dimensions are known at compile time,
then you can dynamically allocate an array of fixed sized arrays:
//----
enum size_t gridSize = 4_000;
enum size_t total = gridSize * gridSize;
static assert (total == 16_000_000); //16 million doubles total
static assert (total * double.sizeof == 128_000_000); //126 Megs
allocated
void main()
{
double[gridSize][] gridInfo = new
double[gridSize][](gridSize);
}
//----
This will give you a dense array: Eg: all the data is contiguous
in memory.
You can also use the "convenient 2D notation":
//----
import std.stdio;
enum gridSize = 4;
enum total = gridSize * gridSize;
void main()
{
double[][] gridInfo = new double[][](gridSize, gridSize);
}
//----
DO NOTE though that in this case, you have a (probably compact
but) jagged array. What this means is that instead of having one
single solid block of data, you have a top level array, that
references a second level of arrays.
EG: It is (should be) equivalent to:
//----
enum size_t gridSize = 4_000;
enum size_t total = gridSize * gridSize;
void main()
{
double[][] gridInfo = new double[][](gridSize); //Create an
array of empty array;
//Initialize gridInfo. Scope block to avoid polution
{
double[] megaBlock = new double[](total); //Create all
the data
foreach (i ; 0 .. gridSize) //Iterate on each gridInfo
entry
{
size_t offset = i * gridSize;
gridInfo[i] = megaBlock[offset .. offset +
gridSize];//Connect the arrays;
}
}
}
//----
It's not a big deal, but indexing *might* be a little slower with
this scheme.
