On 09/09/2011 10:25 PM, teo wrote:
On Fri, 09 Sep 2011 17:43:04 +0200, Timon Gehr wrote:
On 09/09/2011 05:19 PM, teo wrote:
Here is an example of what I am after:
struct DATA
{
ubyte D1;
ubyte D2;
ubyte D3;
ubyte D4;
}
void main()
{
ubyte[16] a = [ 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08,
0x01,
0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08 ];
auto b = (cast(DATA*)a.ptr)[0 .. 4];
auto c = (cast(DATA[]*)b.ptr)[0 .. 2][0 .. 2];
}
I need to have a DATA[2][2]. That code compiles but gives me a
segmentation fault.
If you actually want a dynamic DATA[2][] array of length 2, this works:
auto b=(*(cast(DATA[2][2]*)a.ptr))[];
Otherwise:
A simple reinterpret cast should do:
auto b=*(cast(DATA[2][2]*)a.ptr);
but note that this copies the data, because static arrays have value
semantics.
If you want to have refer the new array to the same location, you can
use a union.
void main(){
union Myunion{
ubyte[16] a = [ 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08,
0x01,
0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08 ];
DATA[2][2] b;
}
Myunion myunion;
assert(*(cast(DATA[2][2]*)myunion.a.ptr)==myunion.b);
}
Thank you Timon for the good explanation.
You are welcome. As bearophile suggests, those are nicer though:
auto b=(cast(DATA[2][2]a); // static array
auto b=(cast(DATA[2][2]a)[];// dynamic array
Just one more question (I suspect the answer will be no, but let me ask):
is it possible to directly cast to ubyte[][]?
Not directly, because you have to build some structure in memory.
an ubyte[][] is an array of dynamic arrays. Each of those dynamic arrays
is a 2 field struct consisting of a ptr and a length field.
That data you have to construct manually.
in case you wanted to turn the ubyte[16] a array to a ubyte[][] b array,
with b.length and b[i].length equal to 4, this would probably do the job:
ubyte[16] a=[ 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x02,
0x03, 0x04, 0x05, 0x06, 0x07, 0x08 ];
auto b=new ubyte[][](4);// create a ubyte[][] array that can hold 4
ubyte[] values
foreach(i,ref x;b) x=a[i*4 .. (i+1)*4]; // compute the values by slicing
the original array
