std::unordered_set swap() method
- since C++17
- until C++17
// Non const version only
void swap( unordered_set& other ) noexcept(/* see below */);
// Non const version only
void swap( unordered_set& other );
Exchanges the contents of the container with those of other
. Does not invoke any move, copy, or swap operations on individual elements.
All iterators and references remain valid.
The past-the-end iterator is invalidated.
The Hash
and KeyEqual
objects must be Swappable
, and they are exchanged using unqualified calls to non-member swap.
- since C++11
If std::allocator_traits<allocator_type>::propagate_on_container_swap::value
is true
, then the allocators are exchanged using an unqualified call to non-member swap.
Otherwise, they are not swapped (and if get_allocator() != other.get_allocator()
, the behavior is undefined).
Parameters
other
- container to exchange the contents with
Return value
(none)
Complexity
Constant - O(1).
Exceptions
- since C++17
- until C++17
noexcept specification:
noexcept(std::allocator_traits<Allocator>::is_always_equal::value
&& std::is_nothrow_swappable<Hash>::value
&& std::is_nothrow_swappable<key_equal>::value)
Hash
or KeyEqual
objects.Example
#include <iostream>
#include <unordered_set>
template<class Os, class Co> Os& operator<<(Os& os, const Co& co) {
os << "{";
for (auto const& i : co) { os << ' ' << i; }
return os << " } ";
}
int main()
{
std::unordered_set<int> a1{3, 1, 3, 2}, a2{5, 4, 5};
auto it1 = std::next(a1.begin());
auto it2 = std::next(a2.begin());
const int& ref1 = *(a1.begin());
const int& ref2 = *(a2.begin());
std::cout << a1 << a2 << *it1 << ' ' << *it2 << ' ' << ref1 << ' ' << ref2 << '\n';
a1.swap(a2);
std::cout << a1 << a2 << *it1 << ' ' << *it2 << ' ' << ref1 << ' ' << ref2 << '\n';
// Note that every iterator referring to an element in one container before the swap
// refers to the same element in the other container after the swap. Same is true
// for references.
}
{ 2 1 3 } { 4 5 } 1 5 2 4
{ 4 5 } { 2 1 3 } 1 5 2 4
Hover to see the original license.