FreeBSD Manual Pages
std::slice(3) C++ Standard Libary std::slice(3) NAME std::slice - std::slice Synopsis Defined in header <valarray> class slice; std::slice is the selector class that identifies a subset of std::valarray similar to BLAS slice. An object of type std::slice holds three values: the starting index, the stride, and the total number of values in the subset. Objects of type std::slice can be used as indexes with valarray's operator[]. Member functions constructor constructs a slice (public member function) start returns the parameters of the slice size (public member function) stride std::slice::slice slice() (1) slice( std::size_t start, std::size_t size, std::size_t stride ); (2) slice( const slice& other ); (3) Constructs a new slice. 1) Default constructor. Equivalent to slice(0, 0, 0). This construc- tor exists only to allow construction of arrays of slices. 2) Constructs a new slice with parameters start, size, stride. This slice will refer to size number of elements, each with the position: start + 0*stride start + 1*stride ... start + (size-1)*stride 3) Constructs a copy of other. Parameters start - the position of the first element size - the number of elements in the slice stride - the number of positions between successive elements in the slice other - another slice to copy std::slice::start, size, stride std::size_t start() const; (1) std::size_t size() const; (2) std::size_t stride() const; (3) Returns the parameters passed to the slice on construction - start, size and stride respectively. Parameters (none) Return value The parameters of the slice -- start, size and stride respectively. Complexity Constant. Non-member functions operator==(std::slice) checks if two slices are equal (C++20) (function) operator==(std::slice) friend bool operator==( const slice& lhs, const slice& rhs ); (since C++20) Checks if the parameters of lhs and rhs - start, size and stride are equal respectively. This function is not visible to ordinary unqualified or qualified lookup, and can only be found by argument-dependent lookup when std::slice is an as- sociated class of the arguments. The != operator is synthesized from operator==. Parameters lhs, rhs - slices to compare Return value lhs.start() == rhs.start() && lhs.size() == rhs.size() && lhs.stride() == rhs.stride() Example Barebones valarray-backed Matrix class with a trace calculating function. // Run this code #include <iostream> #include <valarray> class Matrix { std::valarray<int> data; int dim; public: Matrix(int r, int c) : data(r*c), dim(c) {} int& operator()(int r, int c) {return data[r*dim + c];} int trace() const { return data[std::slice(0, dim, dim+1)].sum(); } }; int main() { Matrix m(3,3); int n = 0; for(int r=0; r<3; ++r) for(int c=0; c<3; ++c) m(r, c) = ++n; std::cout << "Trace of the matrix (1,2,3) (4,5,6) (7,8,9) is " << m.trace() << '\n'; } Output: Trace of the matrix (1,2,3) (4,5,6) (7,8,9) is 15 See also operator[] get/set valarray element, slice, or mask (public member function) generalized slice of a valarray: starting index, set of lengths, set of gslice strides (class) slice_array proxy to a subset of a valarray after applying a slice (class template) http://cppreference.com 2022.07.31 std::slice(3)
NAME | Synopsis | Member functions | Parameters | Parameters | Return value | Complexity | Non-member functions | Parameters | Return value | Example | Output: | See also
Want to link to this manual page? Use this URL:
<https://man.freebsd.org/cgi/man.cgi?query=std::slice&sektion=3&manpath=FreeBSD+Ports+15.0>