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.
| Type | Definition |
|---|---|
value_type | T |
constructs a mask_array (public member function) |
|
destroys a mask_array (public member function) |
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| assigns contents (public member function) |
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| performs arithmetic operation on the array referred by mask. (public member function) |
#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
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