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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 sub- script operator with std::gslice argument. It has reference semantics to a subset of the array 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 in- dex (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 2022.07.31 std::gslice_array(3)
NAME | Synopsis | Member types | Member functions | Example | Output: | See also
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