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std::slice_array

From cppreference.com
< cpp‎ | numeric‎ | valarray
 
 
 
 
 
Defined in header <valarray>
template< class T > class slice_array;

std::slice_array is a helper template used by std::slice subscript operator. It has reference semantics to a subset of the array specified by the std::slice object.

Contents

[edit] Member types

Type Definition
value_type T

[edit] Member functions

constructs a slice_array
(public member function) [edit]
destroys a slice_array
(public member function) [edit]
assigns contents
(public member function) [edit]
performs arithmetic operation on the array referred by slice.
(public member function) [edit]

[edit] Example

#include <iostream>
#include <valarray>
 
class Matrix {
    int dim;
    std::valarray<int> data;
public:
    explicit Matrix(int dim, int init = 0)
        : dim{dim}, data(init, dim*dim) { }
    void clear(int value = 0) { data = value; }
    void identity() { clear(); diagonal() = 1; }
    int& operator()(int x, int y) { return data[dim * y + x]; }
 
    std::slice_array<int> diagonal() {
        return data[std::slice(0, dim, dim+1)];
    }
    std::slice_array<int> secondary_diagonal() {
        return data[std::slice(dim-1, dim, dim-1)];
    }
    std::slice_array<int> row(std::size_t row) {
        return data[std::slice(dim*row, dim, 1)];
    }
    std::slice_array<int> column(std::size_t col) {
        return data[std::slice(col, dim, dim)];
    }
    template<unsigned, unsigned> friend class MatrixStack;
};
 
template <unsigned dim = 3, unsigned max = 8> class MatrixStack {
    std::valarray<int> stack;
    unsigned count = 0;
public:
    MatrixStack() : stack(dim*dim*max) {}
    void print_all() const { 
        std::valarray<int> row(dim*count);
        for (unsigned r = 0; r != dim; ++r) { // screen row
            row = stack[std::gslice(r*dim, {count, dim}, {dim*dim, 1})];
            for (unsigned i = 0; i != row.size(); ++i)
                std::cout << row[i] << ((i+1) % dim ? " " : " │ ");
            std::cout << '\n';
        }
    }
    void push_back(Matrix const& m) {
        if (count < max) {
            stack[std::slice(count * dim * dim, dim * dim, 1)]
                = m.data[std::slice(0, dim * dim, 1)];
            ++count;
        }
    }
};
 
int main()
{
    constexpr int dim = 3;
    Matrix m{dim};
    MatrixStack<dim,12> stack;
 
    m.identity();
    stack.push_back(m);
 
    m.clear(1);
    m.secondary_diagonal() = 3;
    stack.push_back(m);
 
    for (int i = 0; i != dim; ++i) {
        m.clear();
        m.row(i) = i + 1;
        stack.push_back(m);
    }
 
    for (int i = 0; i != dim; ++i) {
        m.clear();
        m.column(i) = i + 1;
        stack.push_back(m);
    }
 
    m.clear();
    m.row(1) = std::valarray<int>{4, 5, 6};
    stack.push_back(m);
 
    m.clear();
    m.column(1) = std::valarray<int>{7, 8, 9};
    stack.push_back(m);
 
    stack.print_all();
}

Output:

1 0 0 │ 1 1 3 │ 1 1 1 │ 0 0 0 │ 0 0 0 │ 1 0 0 │ 0 2 0 │ 0 0 3 │ 0 0 0 │ 0 7 0 │
0 1 0 │ 1 3 1 │ 0 0 0 │ 2 2 2 │ 0 0 0 │ 1 0 0 │ 0 2 0 │ 0 0 3 │ 4 5 6 │ 0 8 0 │
0 0 1 │ 3 1 1 │ 0 0 0 │ 0 0 0 │ 3 3 3 │ 1 0 0 │ 0 2 0 │ 0 0 3 │ 0 0 0 │ 0 9 0 │

[edit] See also

proxy to a subset of a valarray after applying a gslice
(class template) [edit]