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std::valarray::operator=

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valarray<T>& operator=( const valarray<T>& other );
(1)
valarray<T>& operator=( valarray<T>&& other );
(2) (since C++11)
valarray<T>& operator=( const T& val );
(3)
valarray<T>& operator=( const std::slice_array& other);
(4)
valarray<T>& operator=( const std::gslice_array& other);
(5)
valarray<T>& operator=( const std::mask_array& other );
(6)
valarray<T>& operator=( const std::indirect_array& other );
(7)
valarray<T>& operator=( std::initializer_list<T> il );
(8) (since C++11)

Replaces the contents of the numeric array.

1) Copy assignment operator. If the length of other does not equal the length of *this, first resizes as if by resize(other.size()), then replaces each element of *this with a copy of the corresponding element of other
2) Move assignment operator. Replaces the contents of *this with those of other. The value of other is unspecified after this operation. The complexity of this operation may be linear if T has non-trivial destructors, but is usually constant otherwise.
3) Replaces each value in *this with a copy of val.
4-7) Replaces the contents of *this with the result of a generalized subscripting operation. The behavior is undefined if the length of the argument does not equal the length of *this or if any value on the left depends on the value on the right (e.g v=v[v>2]).
8) Assigns the contents of initializer list il. Equivalent to *this = valarray(il).

Contents

[edit] Parameters

other - another numeric array (or a mask) to assign
val - the value to initialize each element with
il - initializer list to assign

[edit] Return value

*this

[edit] Exceptions

1) (none)
2)
noexcept specification:  
noexcept
  
3-8) (none)

[edit] Example

#include <valarray>
#include <iostream>
 
int main()
{
    std::valarray<int> v1(3);
    v1 = -1; // from a scalar 
    std::cout << "assigned from scalar: ";
    for(int n: v1) std::cout << n << ' '; std::cout << '\n';
 
    v1 = {1, 2, 3, 4, 5, 6}; // from initializer list of different size
    std::cout << "assigned from initializer_list:      ";
    for(int n: v1) std::cout << n << ' '; std::cout << '\n';
 
    std::valarray<int> v2(3);
    v2 = v1[std::slice(0,3,2)]; // from slice array
    std::cout << "every 2nd element starting at pos 0: ";
    for(int n: v2) std::cout << n << ' '; std::cout << '\n';
 
    v2 = v1[v1 % 2 == 0]; // from mask array
    std::cout << "values that are even          :      ";
    for(int n: v2) std::cout << n << ' '; std::cout << '\n';
 
    std::valarray<std::size_t> idx = {0,1,2,4}; // index array
    v2.resize(4); // sizes must match when assigning from gen subscript
    v2 = v1[idx]; // from indirect array
    std::cout << "values at positions 0,1,2,4:         ";
    for(int n: v2) std::cout << n << ' '; std::cout << '\n';
}

Output:

assigned from scalar: -1 -1 -1 
assigned from initializer_list:      1 2 3 4 5 6 
every 2nd element starting at pos 0: 1 3 5 
values that are even          :      2 4 6 
values at positions 0,1,2,4:         1 2 3 5