std::mask_array (3) - Linux Manuals

std::mask_array: std::mask_array

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

              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