NAME¶

std::slice_array - std::slice_array

Synopsis¶

Defined in header <valarray>
template< class T > class slice_array;

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

Member types¶

Type Definition
value_type T

Member functions¶

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

Example¶

// Run this code

#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 │

See also¶

gslice_array proxy to a subset of a valarray after applying a gslice
(class template)