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std::gslice_array(3)	       C++ Standard Libary	    std::gslice_array(3)

NAME
     std::gslice_array - std::gslice_array

Synopsis
	Defined in header <valarray>
	template< class T > class gslice_array;

	std::gslice_array  is  a  helper template used by the valarray subscript
     operator with
	std::gslice argument. It has reference semantics to a subset of the  ar-
     ray specified
	by the std::gslice object.

Member types
	Type	   Definition
	value_type T

Member functions
	constructor   constructs a gslice_array
		      (public member function)
	destructor    destroys a gslice_array
		      (public member function)
	operator=     assigns contents
		      (public member function)
	operator+=
	operator-=
	operator*=
	operator/=
	operator%=     performs  arithmetic  operation	on the array referred by
     generic slice.
	operator&=    (public member function)
	operator|=
	operator^=
	operator<<=
	operator>>=

Example
     // Run this code

      #include <cassert>
      #include <cstddef>
      #include <iomanip>
      #include <iostream>
      #include <numeric>
      #include <valarray>

      int main()
      {
	  std::valarray<int> data(32);
	  std::iota(std::begin(data), std::end(data), 0);

	  const std::size_t offset = 1, z = 2, y = 3, x = 4;
	  const std::valarray<std::size_t> sizes{z, y, x};
	  const std::valarray<std::size_t> strides{15, 5, 1};
	  const std::gslice gslice = std::gslice(offset, sizes, strides);
	  // Indices are generated according to the formula:
	  // index[k] = offset + [0,1,2)*15 + [0,1,2,3)*5 + [0,1,2,3,4)*1
	  //	      = offset + inner_product(sizes[k], strides);
	  // where sizes[k] = {[0,z), [0,y), [0,x)}, while the	rightmost  index
     (x)
	  // runs fastest. As a result we have following set of indices:
	  //  index[0]	= 1 + 0*15 + 0*5 + 0*1 = 1
	  //  index[1]	= 1 + 0*15 + 0*5 + 1*1 = 2
	  //  index[2]	= 1 + 0*15 + 0*5 + 2*1 = 3
	  //  index[3]	= 1 + 0*15 + 0*5 + 3*1 = 4
	  //  index[4]	= 1 + 0*15 + 1*5 + 0*1 = 6
	  //  index[5]	= 1 + 0*15 + 1*5 + 1*1 = 7
	  //  index[6]	= 1 + 0*15 + 1*5 + 2*1 = 8
	  //  index[7]	= 1 + 0*15 + 1*5 + 3*1 = 9
	  //  ...
	  //  index[22] = 1 + 1*15 + 2*5 + 2*1 = 28
	  //  index[23] = 1 + 1*15 + 2*5 + 3*1 = 29

	  const std::valarray<int> indices = data[gslice];
	  for (unsigned i = 0; i != indices.size(); ++i)
	      std::cout  << std::setfill('0') << std::setw(2) << indices[i] << '
     ';
	  std::cout << "\nTotal indices: " << indices.size() << '\n';
	  assert(indices.size() == x * y * z);

	  data = 0;
	  std::gslice_array<int> gslice_array = data[gslice];
	  gslice_array = 1;
	  // Cells that correspond to generated indices = '1', skipped	cells  =
     '0'.
	  for (auto i : data)
	      std::cout << i << ' ';
	  std::cout << "\nSum of ones = " << data.sum() << '\n';
      }

Output:
      01 02 03 04 06 07 08 09 11 12 13 14 16 17 18 19 21 22 23 24 26 27 28 29
      Total indices: 24
      0 1 1 1 1 0 1 1 1 1 0 1 1 1 1 0 1 1 1 1 0 1 1 1 1 0 1 1 1 1 0 0
      Sum of ones = 24

See also
	slice_array proxy to a subset of a valarray after applying a slice
		    (class template)

http://cppreference.com 	   2024.06.10		    std::gslice_array(3)
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