From cppreference.com
voidswap(unordered_multimap&other);(since C++11)
(until C++17)voidswap(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
iterator is invalidated. The Hash and KeyEqual objects must be
, 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 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 Complexity
Constant.
Exceptions
Any exception thrown by the swap of the Hash or KeyEqual objects.
(until C++17)
specification:
noexcept(std::allocator_traits<Allocator>::is_always_equal::valueandstd::is_nothrow_swappable<Hash>::valueandstd::is_nothrow_swappable<key_equal>::value)(since C++17)Example
Run this code
importstd;intmain(){std::unordered_multimap<std::string,std::string>m1{{"γ","gamma"},{"β","beta"},{"α","alpha"},{"γ","gamma"}},m2{{"ε","epsilon"},{"δ","delta"},{"ε","epsilon"}};constauto&ref=*(m1.begin());constautoiter=std::next(m1.cbegin());std::println("Before swap:\nm1: {}\nm2: {}\nref: {}\niter: {}",m1,m2,ref,*iter);m1.swap(m2);std::println("After swap:\nm1: {}\nm2: {}\nref: {}\niter: {}",m1,m2,ref,*iter);// 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. The 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