vector<bool> working_lattice(box.rect.length * box.rect.height * box.rect.width);
How do I access working_lattice[1][5][3] using the style of declaration above?
3 Answers
You need to access it as
(i * length * height) + (j * height) + k
So in your case
working_lattice[(i * box.rect.length * box.rect.height) + (j * box.rect.height) + k);
or
working_lattice[(1 * box.rect.length * box.rect.height) + (5 * box.rect.height) + 3);
EDIT: Since you mentioned x, y, z elsewhere
working_lattice[(x * box.rect.length * box.rect.height) + (y * box.rect.height) + z);
1 Comment
josephthomas
Can the downvoter comment as to why? He already accepted it as the answer too
This depends on whether you're using row-major or column-major ordering. Row-major is more typical in C/C++, but you can do either if you're doing it manually.
In row-major ordering, to get to the i, j, k'th element, you need to go through box.rect.height * box.rect.width * i elements to get up to the ith row, plus box.rect.width * j elements to get to the jth column of that row, plus k to get back to the kth element depthwise. To be super-explicit:
const size_t n_x = box.rect.length;
const size_t n_y = box.rect.height;
const size_t n_z = box.rect.width;
working_lattice[1 * n_x * n_z + 5 * n_z + 3]
This is obviously pretty annoying, so you might want to define an inline function or something to help out.
Comments
i.e considering this one:
A[R][S][T]
assuming that its base address is addr_base_A,
so you hope that you can get the address of one specific element A[i][j][k],
the answer I think is: S*T*i + T*j + k + addr_base_A.
Hope this helps :)
1 Comment
Xin
maybe you could draw a pic to help your understanding, I figured it out by doing this.
working_lattice[? * ? * ? + ?]. But how?vector<bool>, I showed a 3D matrix that you can access usingmatrix[a][b][c]notation in an old answer. For the moment, it passes the size as a template parameter, but it wouldn't take a huge amount to pass it as a ctor parameter instead. If I were writing it today, I'd undoubtedly use anstd::vectorinstead of an actual 3D array, which would make it trivial to pass the size to the ctor.