std::map<Key,T,Compare,Allocator>::swap

void swap( map& other );		(until C++17)
void swap( map& 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 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 (and if get_allocator() != other.get_allocator(), the behavior is undefined).

(since C++11)

Parameters

other

-

container to exchange the contents with

Return value

(none)

Exceptions

Any exception thrown by the swap of the `Compare` objects.	(until C++17)
`noexcept` specification: noexcept(std::allocator_traits<Allocator>::is_always_equal::value && std::is_nothrow_swappable<Compare>::value)	(since C++17)

Complexity

Constant.

Example

Run this code

#include <iostream>
#include <string>
#include <utility>
#include <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::map<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.
}

Output:

──────── before swap ────────
m1: { α:alpha β:beta γ:gamma }
m2: { δ:delta ε:epsilon }
ref: α:alpha
iter: β:beta
──────── after swap ────────
m1: { δ:delta ε:epsilon }
m2: { α:alpha β:beta γ:gamma }
ref: α:alpha
iter: β:beta

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Sequence
array (C++11)
vector
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forward_list (C++11)
list
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set
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map
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unordered_set (C++11)
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unordered_map (C++11)
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Adaptors
stack
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Views
span (C++20)

Member functions
map::map
map::~map
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Element access
map::at
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map::beginmap::cbegin (C++11)
map::endmap::cend (C++11)
map::rbeginmap::crbegin (C++11)
map::rendmap::crend (C++11)
Capacity
map::empty
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map::clear
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map::insert_or_assign (C++17)
map::emplace (C++11)
map::emplace_hint (C++11)
map::try_emplace (C++17)
map::erase
map::swap
map::extract (C++17)
map::merge (C++17)
Lookup
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map::find
map::contains (C++20)
map::equal_range
map::lower_bound
map::upper_bound
Observers
map::key_comp
map::value_comp
Non-member functions
std::swap
erase_if (C++20)
operator==operator!=operator<operator>operator<=operator>=operator<=> (until C++20)(until C++20)(until C++20)(until C++20)(until C++20)(C++20)
Deduction guides (C++17)