NAME¶

std::mask_array - std::mask_array

Synopsis¶

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

std::mask_array is a helper template used by the valarray subscript operator with
std::valarray<bool> argument. It has reference semantics and provides access to the
subset of the valarray consisting of the elements whose indices correspond to true
values in the std::valarray<bool> mask.

Member types¶

Type Definition
value_type T

Member functions¶

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

Example¶

// Run this code

#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;
// 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(int n: data) std::cout << n << ' ';
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