Difference between revisions of "cpp/numeric/valarray/mask array"
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Revision as of 02:48, 4 May 2017
| Defined in header <valarray>
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| template< class T > class mask_array; |
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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 (public member function) | |
destroys a mask_array (public member function) | |
| assigns contents (public member function) | |
| 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
