std::mask_array (3) Linux Manual Page

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

              constructs a mask_array
constructor (public member function)
              destroys a mask_array
destructor (public member function)
              assigns contents
operator= (public member function)

operator+=
operator-=
operator*=
operator/= performs arithmetic operation on the array referred by mask.
operator%= (public member function)
operator&=
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