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std::multiset swap() method

// Non const version only
void swap( multiset& other ) noexcept(/* see below */);

Exchanges the contents of the container with those of other. Does not invoke any move, copy, or swap operations on individual elements.

Invalidation

The past-the-end iterator is invalidated.

All other iterators and references remain valid.

The Compare objects must be Swappable, and they are exchanged using unqualified call 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 non-member swap.

Otherwise, they are not swapped.

Undefined behaviour

If get_allocator() != other.get_allocator(), the behavior is undefined.

Parameters

  • other - container to exchange the contents with

Return value

(none)

Exceptions

noexcept specification:
noexcept(std::allocator_traits<Allocator>::is_always_equal::value
&& std::is_nothrow_swappable<Compare>::value)

Complexity

Constant - O(1).

Example

Main.cpp
#include <functional>
#include <iostream>
#include <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::multiset<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.

struct Cmp : std::less<int> {
int id{};
Cmp(int i) : id{i} { }
};

std::multiset<int, Cmp> s1{ {2, 2, 1, 1}, Cmp{6} }, s2{ {4, 4, 3, 3}, Cmp{9} };

std::cout << s1 << s2 << s1.key_comp().id << ' ' << s2.key_comp().id << '\n';
s1.swap(s2);
std::cout << s1 << s2 << s1.key_comp().id << ' ' << s2.key_comp().id << '\n';

// So, comparator objects (Cmp) are also exchanged after the swap.
}
Output
{ 1 2 3 3 } { 4 5 5 } 2 5 1 4
{ 4 5 5 } { 1 2 3 3 } 2 5 1 4
{ 1 1 2 2 } { 3 3 4 4 } 6 9
{ 3 3 4 4 } { 1 1 2 2 } 9 6
This article originates from this CppReference page. It was likely altered for improvements or editors' preference. Click "Edit this page" to see all changes made to this document.
Hover to see the original license.

std::multiset swap() method

// Non const version only
void swap( multiset& other ) noexcept(/* see below */);

Exchanges the contents of the container with those of other. Does not invoke any move, copy, or swap operations on individual elements.

Invalidation

The past-the-end iterator is invalidated.

All other iterators and references remain valid.

The Compare objects must be Swappable, and they are exchanged using unqualified call 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 non-member swap.

Otherwise, they are not swapped.

Undefined behaviour

If get_allocator() != other.get_allocator(), the behavior is undefined.

Parameters

  • other - container to exchange the contents with

Return value

(none)

Exceptions

noexcept specification:
noexcept(std::allocator_traits<Allocator>::is_always_equal::value
&& std::is_nothrow_swappable<Compare>::value)

Complexity

Constant - O(1).

Example

Main.cpp
#include <functional>
#include <iostream>
#include <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::multiset<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.

struct Cmp : std::less<int> {
int id{};
Cmp(int i) : id{i} { }
};

std::multiset<int, Cmp> s1{ {2, 2, 1, 1}, Cmp{6} }, s2{ {4, 4, 3, 3}, Cmp{9} };

std::cout << s1 << s2 << s1.key_comp().id << ' ' << s2.key_comp().id << '\n';
s1.swap(s2);
std::cout << s1 << s2 << s1.key_comp().id << ' ' << s2.key_comp().id << '\n';

// So, comparator objects (Cmp) are also exchanged after the swap.
}
Output
{ 1 2 3 3 } { 4 5 5 } 2 5 1 4
{ 4 5 5 } { 1 2 3 3 } 2 5 1 4
{ 1 1 2 2 } { 3 3 4 4 } 6 9
{ 3 3 4 4 } { 1 1 2 2 } 9 6
This article originates from this CppReference page. It was likely altered for improvements or editors' preference. Click "Edit this page" to see all changes made to this document.
Hover to see the original license.