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std::unordered_multimap::swap(3) | C++ Standard Libary | std::unordered_multimap::swap(3) |
NAME¶
std::unordered_multimap::swap - std::unordered_multimap::swap
Synopsis¶
void swap( unordered_multimap& other ); (since C++11)
(until C++17)
void swap( unordered_multimap& other ) noexcept(/* see below */);
(since C++17)
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.
If
std::allocator_traits<allocator_type>::propagate_on_container_swap::value
is true, then the allocators are exchanged using an unqualified call to
(since
non-member swap. Otherwise, they are not swapped (and if get_allocator() !=
C++11)
other.get_allocator(), the behavior is undefined).
Parameters¶
other - container to exchange the contents with
Return value¶
(none)
Exceptions¶
Any exception thrown by the swap of the Hash or KeyEqual objects.
(until C++17)
noexcept specification:
noexcept(std::allocator_traits<Allocator>::is_always_equal::value
(since C++17)
&& std::is_nothrow_swappable<Hash>::value
&& std::is_nothrow_swappable<key_equal>::value)
Complexity¶
Constant.
Example¶
// Run this code
#include <iostream>
#include <string>
#include <utility>
#include <unordered_map>
// print out a std::pair
template <class Os, class U, class V>
Os& operator<<(Os& os, const std::pair<U, V>& p) {
return os << p.first << ":" << p.second;
}
// print out a container
template <class Os, class Co>
Os& operator<<(Os& os, const Co& co) {
os << "{";
for (auto const& i : co) { os << ' ' << i; }
return os << " }\n";
}
int main()
{
std::unordered_multimap<std::string, std::string>
m1 { {"γ", "gamma"}, {"β",
"beta"}, {"α", "alpha"},
{"γ", "gamma"}, },
m2 { {"ε", "epsilon"}, {"δ",
"delta"}, {"ε", "epsilon"} };
const auto& ref = *(m1.begin());
const auto iter = std::next(m1.cbegin());
std::cout <<
"────────
before swap
────────\n"
<< "m1: " << m1 << "m2: " << m2
<< "ref: " << ref
<< "\niter: " << *iter << '\n';
m1.swap(m2);
std::cout <<
"──────── after
swap
────────\n"
<< "m1: " << m1 << "m2: " << m2
<< "ref: " << ref
<< "\niter: " << *iter << '\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.
}
Possible output:¶
────────
before swap ────────
m1: { α:alpha β:beta γ:gamma γ:gamma }
m2: { δ:delta ε:epsilon ε:epsilon }
ref: α:alpha
iter: β:beta
──────── after swap
────────
m1: { δ:delta ε:epsilon ε:epsilon }
m2: { α:alpha β:beta γ:gamma γ:gamma }
ref: α:alpha
iter: β:beta
See also¶
std::swap(std::unordered_multimap) specializes the std::swap
algorithm
(C++11) (function template)
2022.07.31 | http://cppreference.com |