< cpp‎ | container‎ | unordered set
Revision as of 18:18, 2 November 2012 by P12bot (Talk | contribs)

(diff) ← Older revision | Latest revision (diff) | Newer revision → (diff)
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.


[edit] Parameters

other - another container to use as data source
ilist - initializer list to use as data source

[edit] Return value


[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.


noexcept specification:  

&& std::is_nothrow_move_assignable<Hash>::value

&& std::is_nothrow_move_assignable<Pred>::value)
(since C++17)

[edit] Example

The following code uses to assign one std::unordered_set to another:

#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);


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) [edit]