Boost:MultiArray
MultiArray exports information regarding the memory layout of its contained elements. Its memory model for elements is completely defined by 4 properties: the origin, shape, index bases, and strides. The origin is the address in memory of the element accessed as a[0][0]...[0], where a is a MultiArray. The shape is a list of numbers specifying the size of containers at each dimension. For example, the first extent is the size of the outermost container, the second extent is the size of its subcontainers, and so on. The index bases are a list of signed values specifying the index of the first value in a container. All containers at the same dimension share the same index base. Note that since positive index bases are possible, the origin need not exist in order to determine the location in memory of the MultiArray's elements. The strides determine how index values are mapped to memory offsets. They accomodate a number of possible element layouts. For example, the elements of a 2 dimensional array can be stored by row (i.e., the elements of each row are stored contiguously) or by column (i.e., the elements of each column are stored contiguously).
strides
메모리 오프셋에 변수를 위치시키는 방법을 정의한다.
Simple example
#include "boost/multi_array.hpp"
#include <cassert>
int
main () {
// Create a 3D array that is 3 x 4 x 2
typedef boost::multi_array<double, 3> array_type;
typedef array_type::index index;
array_type A(boost::extents[3][4][2]);
// Assign values to the elements
int values = 0;
for(index i = 0; i != 3; ++i)
for(index j = 0; j != 4; ++j)
for(index k = 0; k != 2; ++k)
A[i][j][k] = values++;
// Verify values
int verify = 0;
for(index i = 0; i != 3; ++i)
for(index j = 0; j != 4; ++j)
for(index k = 0; k != 2; ++k)
assert(A[i][j][k] == verify++);
return 0;
}
Resizing an Array
typedef boost::multi_array<int, 3> array_type;
array_type::extent_gen extents;
array_type A(extents[3][3][3]);
A[0][0][0] = 4;
A[2][2][2] = 5;
A.resize(extents[2][3][4]);
assert(A[0][0][0] == 4);
// A[2][2][2] is no longer valid.