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std::unordered_multimap<Key,T,Hash,KeyEqual,Allocator>:: unordered_multimap

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C++
Containers library
std::unordered_multimap
Member types
Member functions
Non-member functions
Deduction guides (C++17)
(1)
unordered_multimap ( )
: unordered_multimap ( size_type ( /* unspecified */ ) ) { }
(since C++11)
(until C++20)
unordered_multimap ( ) ;
(since C++20)
explicit unordered_multimap ( size_type bucket_count,

const Hash & hash = Hash ( ) ,
const key_equal & equal = key_equal ( ) ,

const Allocator & alloc = Allocator ( ) ) ;
(2) (since C++11)
unordered_multimap ( size_type bucket_count,

const Allocator & alloc )

: unordered_multimap ( bucket_count, Hash ( ) , key_equal ( ) , alloc ) { }
(3) (since C++14)
unordered_multimap ( size_type bucket_count,

const Hash & hash,
const Allocator & alloc )

: unordered_multimap ( bucket_count, hash, key_equal ( ) , alloc ) { }
(4) (since C++14)
explicit unordered_multimap ( const Allocator & alloc ) ;
(5) (since C++11)
template < class InputIt >

unordered_multimap ( InputIt first, InputIt last,
size_type bucket_count = /* unspecified */ ,
const Hash & hash = Hash ( ) ,
const key_equal & equal = key_equal ( ) ,

const Allocator & alloc = Allocator ( ) ) ;
(6) (since C++11)
template < class InputIt >

unordered_multimap ( InputIt first, InputIt last,
size_type bucket_count,
const Allocator & alloc )
: unordered_multimap ( first, last,

bucket_count, Hash ( ) , key_equal ( ) , alloc ) { }
(7) (since C++14)
template < class InputIt >

unordered_multimap ( InputIt first, InputIt last,
size_type bucket_count,
const Hash & hash,
const Allocator & alloc )
: unordered_multimap ( first, last,

bucket_count, hash, key_equal ( ) , alloc ) { }
(8) (since C++14)
unordered_multimap ( const unordered_multimap & other ) ;
(9) (since C++11)
unordered_multimap ( const unordered_multimap & other, const Allocator & alloc ) ;
(10) (since C++11)
unordered_multimap ( unordered_multimap && other ) ;
(11) (since C++11)
unordered_multimap ( unordered_multimap && other, const Allocator & alloc ) ;
(12) (since C++11)
unordered_multimap ( std:: initializer_list < value_type > init,

size_type bucket_count = /* unspecified */ ,
const Hash & hash = Hash ( ) ,
const key_equal & equal = key_equal ( ) ,

const Allocator & alloc = Allocator ( ) ) ;
(13) (since C++11)
unordered_multimap ( std:: initializer_list < value_type > init,

size_type bucket_count,
const Allocator & alloc )
: unordered_multimap ( init, bucket_count,

Hash ( ) , key_equal ( ) , alloc ) { }
(14) (since C++14)
unordered_multimap ( std:: initializer_list < value_type > init,

size_type bucket_count,
const Hash & hash,
const Allocator & alloc )
: unordered_multimap ( init, bucket_count,

hash, key_equal ( ) , alloc ) { }
(15) (since C++14)
template < container-compatible-range < value_type > R >

unordered_multimap ( std:: from_range_t , R && rg,
size_type bucket_count = /* see description */ ,
const Hash & hash = Hash ( ) ,
const key_equal & equal = key_equal ( ) ,

const Allocator & alloc = Allocator ( ) ) ;
(16) (since C++23)
template < container-compatible-range < value_type > R >

unordered_multimap ( std:: from_range_t , R && rg,
size_type bucket_count,
const Allocator & alloc )
: unordered_multimap ( std:: from_range , std:: forward < R > ( rg ) ,

bucket_count, Hash ( ) , key_equal ( ) , alloc ) { }
(17) (since C++23)
template < container-compatible-range < value_type > R >

unordered_multimap ( std:: from_range_t , R && rg,
size_type bucket_count,
const Hash & hash,
const Alloc & alloc )
: unordered_multimap ( std:: from_range , std:: forward < R > ( rg ) ,

bucket_count, hash, key_equal ( ) , alloc ) { }
(18) (since C++23)

Constructs new container from a variety of data sources. Optionally uses user supplied bucket_count as a minimal number of buckets to create, hash as the hash function, equal as the function to compare keys and alloc as the allocator.

1-5) Constructs empty container. Sets max_load_factor() to 1.0 . For the default constructor, the number of buckets is unspecified.
6-8) Constructs the container with the contents of the range [ first , last ) . Sets max_load_factor() to 1.0 .
9,10) Copy constructor. Constructs the container with the copy of the contents of other , copies the load factor, the predicate, and the hash function as well. If alloc is not provided, allocator is obtained by calling std:: allocator_traits < allocator_type > :: select_on_container_copy_construction ( other. get_allocator ( ) ) .

The template parameter Allocator is only deduced from the first argument while used in class template argument deduction .

(since C++23)
11,12) Move constructor . Constructs the container with the contents of other using move semantics. If alloc is not provided, allocator is obtained by move-construction from the allocator belonging to other .

The template parameter Allocator is only deduced from the first argument while used in class template argument deduction .

(since C++23)
13-15) Initializer-list constructor . Constructs the container with the contents of the initializer list init , same as unordered_multimap ( init. begin ( ) , init. end ( ) ) .
16-18) Constructs the container with the contents of rg .

Contents

Parameters

alloc - allocator to use for all memory allocations of this container
bucket_count - minimal number of buckets to use on initialization. If it is not specified, an unspecified default value is used
hash - hash function to use
equal - comparison function to use for all key comparisons of this container
first, last - the pair of iterators defining the source range of elements to copy
rg - a container compatible range , that is, an input_range whose elements are convertible to value_type
other - another container to be used as source to initialize the elements of the container with
init - initializer list to initialize the elements of the container with
Type requirements
-
InputIt must meet the requirements of LegacyInputIterator .

Complexity

1-5) Constant.
6-8) Average case linear (i.e. O(N) , where N is std:: distance ( first, last ) ), worst case quadratic, i.e. O(N 2 ) .
9,10) Linear in size of other .
11,12) Constant. If alloc is given and alloc ! = other. get_allocator ( ) , then linear.
13-15) Average case O(N) ( N is std:: size ( init ) ), worst case O(N 2 ) .
16-18) Average case O(N) ( N is ranges:: distance ( rg ) ), worst case O(N 2 ) .

Exceptions

Calls to Allocator::allocate may throw.

Notes

After container move construction (overload ( 11,12 ) ), references, pointers, and iterators (other than the end iterator) to other remain valid, but refer to elements that are now in * this . The current standard makes this guarantee via the blanket statement in [container.reqmts]/67 , and a more direct guarantee is under consideration via LWG issue 2321 .

Although not formally required until C++23, some implementations have already put the template parameter Allocator into non-deduced contexts in earlier modes.

Feature-test macro Value Std Feature
__cpp_lib_containers_ranges 202202L (C++23) Ranges-aware construction and insertion; overloads ( 16-18 )

Example

This section is incomplete
Reason: no example

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR Applied to Behavior as published Correct behavior
LWG 2193 C++11 the default constructor ( 1 ) was explicit made non-explicit
LWG 2230 C++11 the semantics of overload ( 13 ) was not specified specified

See also

assigns values to the container
(public member function)