std::mask_array

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std::valarray

Member functions
valarray::valarray valarray::~valarray valarray::operator= valarray::operator[] valarray::swap valarray::size valarray::resize valarray::sum valarray::min valarray::max valarray::shift valarray::cshift valarray::apply	valarray::operator+valarray::operator-valarray::operator~valarray::operator! valarray::operator+=valarray::operator-=valarray::operator*=valarray::operator/=valarray::operator%=valarray::operator&=valarray::operator|=valarray::operator^=valarray::operator<<=valarray::operator>>=
Non-member functions
swap (C++11) begin (C++11) end (C++11) abs exp log log10 pow sqrt sin cos tan asin acos atan atan2 sinh cosh tanh	operator*operator/operator%operator+operator-operator^operator&operator|operator<<operator>>operator&&operator|| operator==operator!=operator<operator>operator<=operator>=
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slice_array gslice_array indirect_array	slice gslice mask_array
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std::mask_array

Member functions

mask_array::mask_array

mask_array::~mask_array

mask_array::operator=

mask_array::operator+=mask_array::operator-=mask_array::operator*=mask_array::operator/=mask_array::operator%=mask_array::operator&=mask_array::operator|=mask_array::operator^=mask_array::operator<<=mask_array::operator>>=

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%=operator&=operator|=operator^=operator<<=operator>>=	performs arithmetic operation on the array referred by mask. (public member function)

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