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Showing content from https://cplusplus.com/reference/valarray/gslice/ below:

class

std::gslice

Valarray generalized slice selector

This class represents a valarray generalized slice selector (a multidimensional slice). It does not contain nor refers to any element - it only describes a selection of elements to be used as an index in valarray::operator[].

A valarray generalized slice is specified by a starting index, a set of sizes, and a set of strides. It produces a multidimensional combination of slice selections, where:

The starting index (start) is the index of the first element in the selection.

The size (size) is the number of elements in the selection.
The stride (stride) is the span that separates the elements selected.

For example, a gslice with:

 start = 1

  size = {2, 3}

  stride = {7, 2}

would select:

                    [0][1][2][3][4][5][6][7][8][9][10][11][12][13]
start=1:                *
                        |
size=2, stride=7:       *--------------------*
                        |                    |
size=3, stride=2:       *-----*-----*        *------*------*
                        |     |     |        |      |      |
gslice:                 *     *     *        *      *      *
                    [0][1][2][3][4][5][6][7][8][9][10][11][12][13]

Member functions

(constructor): gslice constructor (public member function)

gslice::start: Return start of gslice (public member function)

gslice::size: Return sizes of gslice (public member function)

gslice::stride: Return strides of gslice (public member function)

Example

// gslice example
#include <iostream>     // std::cout
#include <cstddef>      // std::size_t
#include <valarray>     // std::valarray, std::gslice

int main ()
{
  std::valarray<int> foo (14);
  for (int i=0; i<14; ++i) foo[i]=i;

  std::size_t start=1;
  std::size_t lengths[]= {2,3};
  std::size_t strides[]= {7,2};

  std::gslice mygslice (start,
                        std::valarray<std::size_t>(lengths,2),
                        std::valarray<std::size_t>(strides,2));

  std::valarray<int> bar = foo[mygslice];

  std::cout << "gslice:";
  for (std::size_t n=0; n<bar.size(); n++)
	  std::cout << ' ' << bar[n];
  std::cout << '\n';

  return 0;
}

Output

See also

slice: Valarray slice selector (class)

gslice_array: Valarray gslice selection (class template)

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