C++ In a Nutshell

Name

slice class — Slice of an array

Synopsis

class slice {
public:
  slice(  );
  slice(size_t, size_t, size_t);
  size_t start(  ) const;
  size_t size(  ) const;
  size_t stride(  ) const;
};

The slice class describes a slice of a valarray. A slice is a subset of the elements of a valarray at periodic indices. The slice has a starting index, a size, and a stride, in which the stride is the index interval. Figure 13-28 depicts slice(1,3,4) of a valarray.

Figure 13-28. Slicing a valarray

Use the subscript operator to take a slice of a valarray. You can assign a valarray to a slice, in which the righthand side of the assignment must have the same size as the size of the slice. You can also convert the slice to a valarray, which copies only those elements of the slice to the new valarray.

When you take a slice of a valarray, the result is a slice_array object, but the slice_array type is mostly transparent to the programmer. See slice_array later in this section for details.

You can use a slice to treat a valarray as a two-dimensional matrix. A slice can specify a row or column of the matrix. For an n × m matrix, row r is slice(r*m, m, 1), and column c is slice(c, n, m), as you can see in Example 13-46.

Example

Example 13-46. A simple 2-D matrix class

template<typename T> class matrix2D { public: matrix2D(std::size_t rows, std::size_t columns) : rows_(rows), cols_(columns), data_(rows * columns) {} std::size_t ...