class template
<valarray>
std::indirect_array
template <class T> indirect_array;
Valarray indirect selection
This class is used as an intermediate type returned by valarray's subscript operator (operator[]) when used with a valarray of indices.
It references the elements from the valarray whose index is included in the object passed to the subscript operator.
The type is convertible to a valarray (see valarray constructor), producing a new object with copies of the referred elements.
Objects of this type are obtained as the return value of a call to
valarray::operator[]. They cannot be directly
constructed nor copied. It is declared as:
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template <class T> class indirect_array {
public:
typedef T value_type;
void operator= (const valarray<T>&) const;
void operator*= (const valarray<T>&) const;
void operator/= (const valarray<T>&) const;
void operator%= (const valarray<T>&) const;
void operator+= (const valarray<T>&) const;
void operator-= (const valarray<T>&) const;
void operator^= (const valarray<T>&) const;
void operator&= (const valarray<T>&) const;
void operator|= (const valarray<T>&) const;
void operator<<= (const valarray<T>&) const;
void operator>>= (const valarray<T>&) const;
void operator=(const T&);
~indirect_array();
private:
indirect_array();
indirect_array(const indirect_array&);
indirect_array& operator= (const indirect_array&);
};
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Objects of this type are obtained as the return value of a call to
valarray::operator[]. They cannot be
default-constructed, but can be copied. It is declared as:
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template <class T> class indirect_array {
public:
typedef T value_type;
void operator= (const valarray<T>&) const;
void operator*= (const valarray<T>&) const;
void operator/= (const valarray<T>&) const;
void operator%= (const valarray<T>&) const;
void operator+= (const valarray<T>&) const;
void operator-= (const valarray<T>&) const;
void operator^= (const valarray<T>&) const;
void operator&= (const valarray<T>&) const;
void operator|= (const valarray<T>&) const;
void operator<<= (const valarray<T>&) const;
void operator>>= (const valarray<T>&) const;
void operator=(const T&);
indirect_array() = delete;
indirect_array(const gslice_array&);
const indirect_array& operator= (const indirect_array&) const;
~indirect_array();
};
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Example
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// indirect_array example
#include <iostream> // std::cout
#include <cstddef> // std::size_t
#include <valarray> // std::valarray
int main ()
{
std::valarray<int> foo (8);
for (int i=0; i<8; ++i) foo[i]=i; // 0 1 2 3 4 5 6 7
std::size_t sel[] = {3,5,6};
std::valarray<std::size_t> selection (sel,3); // * * *
foo[selection] *= std::valarray<int>(10,3); // 0 1 2 30 4 50 60 7
foo[selection] = 0; // 0 1 2 0 4 0 0 7
std::cout << "foo:";
for (std::size_t i=0; i<foo.size(); ++i)
std::cout << ' ' << foo[i];
std::cout << '\n';
return 0;
}
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Output:
See also
- slice_array
- Valarray slice selection (class template
)
- gslice_array
- Valarray gslice selection (class template
)
- mask_array
- Valarray mask selection (class template
)