std::unordered_set::operator=
From cppreference.com
< cpp | container | unordered set
| unordered_set& operator=( const unordered_set& other );
|
(1) | (since C++11) |
| unordered_set& operator=( unordered_set&& other );
|
(2) | (since C++11) |
| unordered_set& operator=( std::initializer_list<value_type> ilist );
|
(3) | (since C++11) |
Replaces the contents of the container.
1) Copy assignment operator. Replaces the contents with a copy of the contents of
other.If std::allocator_traits<allocator_type>::propagate_on_container_copy_assignment() is true, the target allocator is replaced by a copy of the source allocator. If the target and the source allocators do not compare equal, the target (*this) allocator is used to deallocate the memory, then other's allocator is used to allocate it before copying the elements. (since C++11)
2) Move assignment operator. Replaces the contents with those of
other using move semantics (i.e. the data in other is moved from other into this container). other is in a valid but unspecified state afterwards. If std::allocator_traits<allocator_type>::propagate_on_container_move_assignment() is true, the target allocator is replaced by a copy of the source allocator. If it is false and the source and the target allocators do not compare equal, the target cannot take ownership of the source memory and must move-assign each element individually, allocating additional memory using its own allocator as needed.
3) Replaces the contents with those identified by initializer list
ilist.
Contents |
[edit] Parameters
| other | - | another container to use as data source |
| ilist | - | initializer list to use as data source |
[edit] Return value
*this
[edit] Complexity
1) Linear in the size of the
other.
2) Constant unless std::allocator_traits<allocator_type>::propagate_on_container_move_assignment() is false and the allocators do not compare equal (in which case linear).
3) Linear in the size of
ilist.
Exceptions
2)
noexcept specification:
noexcept(std::allocator_traits<Allocator>::is_always_equal::value
&& std::is_nothrow_move_assignable<Hash>::value |
(since C++17) |
[edit] Notes
After container move assignment (overload (2)), unless elementwise move assignment is forced by incompatible allocators, references, pointers, and iterators (other than the end iterator) to other remain valid, but refer to elements that are now in *this. The current standard makes this guarantee via the blanket statement in §23.2.1[container.requirements.general]/12, and a more direct guarantee is under consideration via LWG 2321.
[edit] Example
The following code uses to assign one std::unordered_set to another:
Run this code
#include <unordered_set> #include <iostream> void display_sizes(const std::unordered_set<int> &nums1, const std::unordered_set<int> &nums2, const std::unordered_set<int> &nums3) { std::cout << "nums1: " << nums1.size() << " nums2: " << nums2.size() << " nums3: " << nums3.size() << '\n'; } int main() { std::unordered_set<int> nums1 {3, 1, 4, 6, 5, 9}; std::unordered_set<int> nums2; std::unordered_set<int> nums3; std::cout << "Initially:\n"; display_sizes(nums1, nums2, nums3); // copy assignment copies data from nums1 to nums2 nums2 = nums1; std::cout << "After assigment:\n"; display_sizes(nums1, nums2, nums3); // move assignment moves data from nums1 to nums3, // modifying both nums1 and nums3 nums3 = std::move(nums1); std::cout << "After move assigment:\n"; display_sizes(nums1, nums2, nums3); }
Output:
Initially: nums1: 6 nums2: 0 nums3: 0 After assigment: nums1: 6 nums2: 6 nums3: 0 After move assigment: nums1: 0 nums2: 6 nums3: 6
[edit] See also
constructs the unordered_set (public member function) |