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C++ valarray Library - Function operator[]
Description
It access element or subscript.
Declaration
Following is the declaration for std::valarray::operator[] function.
T operator[] (size_t n) const; T& operator[] (size_t n);
C++11
const T& operator[] (size_t n) const; T& operator[] (size_t n);
Parameters
n − It is the position of an element in the valarray.
slc − It is a slice object specifying which elements of the valarray are selected.
gslc − It is a gslice object specifying which elements of the valarray are selected.
msk − It is a valarray
with its elements identifying whether each element of *this is selected or not: If an element in *this has its corresponding element in msk set to true it is part of the returned sub-array, otherwise it is not.. ind − It is a valarray
with its elements identifying which elements of *this are selected: Each element in ind is the index of an element in *this that will be part of the returned sub-array.
Return Value
It returns *this.
Exceptions
Basic guarantee − if any operation performed on the elements throws an exception.
Data races
All elements effectively copied are accessed.
Example
In below example explains about std::valarray::operator[] function.
#include <iostream> #include <valarray> int main () { std::valarray<int> myarray (10); myarray[std::slice(2,3,3)]=10; size_t lengths[]={2,2}; size_t strides[]={6,2}; myarray[std::gslice(1, std::valarray<size_t>(lengths,2), std::valarray<size_t>(strides,2))]=20; std::valarray<bool> mymask (10); for (int i=0; i<10; ++i) mymask[i]= ((i%2)==0); myarray[mymask] += std::valarray<int>(3,5); //indirect: size_t sel[]= {2,5,7}; std::valarray<size_t> myselection (sel,3); myarray[myselection]=99; std::cout << "myarray: "; for (size_t i=0; i<myarray.size(); ++i) std::cout << myarray[i] << ' '; std::cout << '\n'; return 0; }
Let us compile and run the above program, this will produce the following result −
myarray: 3 20 99 20 3 99 3 99 13 20