(1) | ||
T operator[]( std::size_t pos ) const; | (until C++11) | |
const T& operator[]( std::size_t pos ) const; | (since C++11) | |
T& operator[]( std::size_t pos ); | (2) | |
std::valarray<T> operator[]( std::slice slicearr ) const; | (3) | |
std::slice_array<T> operator[]( std::slice slicearr ); | (4) | |
std::valarray<T> operator[]( const std::gslice& gslicearr ) const; | (5) | |
std::gslice_array<T> operator[]( const std::gslice& gslicearr ); | (6) | |
std::valarray<T> operator[]( const valarray<bool>& boolarr ) const; | (7) | |
std::mask_array<T> operator[]( const valarray<bool>& boolarr ); | (8) | |
std::valarray<T> operator[]( const valarray<std::size_t>& indarr ) const; | (9) | |
std::indirect_array<T> operator[]( const valarray<std::size_t>& indarr ); | (10) |
Retrieve single elements or portions of the array.
The const
overloads that return element sequences create a new std::valarray
object. The non-const
overloads return classes holding references to the array elements.
std::valarray
object containing copies of the selected items(none).
The selected elements must exist.
i
and j
, the following properties are true: (a[i] = q, a[i]) == q
For a non-const a
.&a[i+j] == &a[i] + j
This means that valarray elements are adjacent in memory.&a[i] != &b[j]
a
and b
that are not aliases of one another. For overloads (3,5,7,9), The function can be implemented with the return type different from std::valarray
. In this case, the replacement type has the following properties:
const
member functions of std::valarray
are provided. std::valarray
, std::slice_array
, std::gslice_array
, std::mask_array
and std::indirect_array
can be constructed from the replacement type. const std::valarray&
except begin()
and end()
(since C++11) should also accept the replacement type. const std::valarray&
should accept every combination of const std::valarray&
and the replacement type. Slice/mask/indirect index accesses do not chain: v[v==n][std::slice(0,5,2)] = x;
is an error because std::mask_array
(the type of v[v==n]
) does not have operator[]
.
#include <iostream> #include <valarray> int main() { std::valarray<int> data = {0,1,2,3,4,5,6,7,8,9}; std::cout << "Initial valarray: "; for(int n: data) std::cout << n << ' '; std::cout << '\n'; data[data > 5] = -1; // valarray<bool> overload of operator[] // the type of data>5 is std::valarray<bool> // the type of data[data>5] is std::mask_array<int> std::cout << "After v[v>5]=-1: "; for(std::size_t n = 0; n < data.size(); ++n) std::cout << data[n] << ' '; // regular operator[] std::cout << '\n'; }
Output:
Initial valarray: 0 1 2 3 4 5 6 7 8 9 After v[v>5]=-1: 0 1 2 3 4 5 -1 -1 -1 -1
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