class template

<set>

std::multiset

template < class T,                        // multiset::key_type/value_type
           class Compare = less<T>,        // multiset::key_compare/value_compare
           class Alloc = allocator<T> >    // multiset::allocator_type
           > class multiset;

Multiple-key set

Multisets are containers that store elements following a specific order, and where multiple elements can have equivalent values.

In a multiset, the value of an element also identifies it (the value is itself the key, of type T). The value of the elements in a multiset cannot be modified once in the container (the elements are always const), but they can be inserted or removed from the container.

Internally, the elements in a multiset are always sorted following a specific strict weak ordering criterion indicated by its internal comparison object (of type Compare).

multiset containers are generally slower than unordered_multiset containers to access individual elements by their key, but they allow the direct iteration on subsets based on their order.

Multisets are typically implemented as binary search trees.

Container properties

Associative: Elements in associative containers are referenced by their key and not by their absolute position in the container.
Ordered: The elements in the container follow a strict order at all times. All inserted elements are given a position in this order.
Set: The value of an element is also the key used to identify it.
Multiple equivalent keys: Multiple elements in the container can have equivalent keys.
Allocator-aware: The container uses an allocator object to dynamically handle its storage needs.

Template parameters

T: Type of the elements. Each element in a multiset container is also identified by this value (each value is itself also the element's key).
Aliased as member types multiset::key_type and multiset::value_type.
Compare: A binary predicate that takes two arguments of the same type as the elements and returns a bool. The expression comp(a,b), where comp is an object of this type and a and b are key values, shall return true if a is considered to go before b in the strict weak ordering the function defines.
The multiset object uses this expression to determine both the order the elements follow in the container and whether two element keys are equivalent (by comparing them reflexively: they are equivalent if !comp(a,b) && !comp(b,a)).
This can be a function pointer or a function object (see constructor for an example). This defaults to less<T>, which returns the same as applying the less-than operator (a<b).
Aliased as member types multiset::key_compare and multiset::value_compare.
Alloc: Type of the allocator object used to define the storage allocation model. By default, the allocator class template is used, which defines the simplest memory allocation model and is value-independent.
Aliased as member type multiset::allocator_type.

Member types

member type	definition	notes
`key_type`	The first template parameter (`T`)
`value_type`	The first template parameter (`T`)
`key_compare`	The second template parameter (`Compare`)	defaults to: `less<key_type>`
`value_compare`	The second template parameter (`Compare`)	defaults to: `less<value_type>`
`allocator_type`	The third template parameter (`Alloc`)	defaults to: `allocator<value_type>`
`reference`	`allocator_type::reference`	for the default allocator: `value_type&`
`const_reference`	`allocator_type::const_reference`	for the default allocator: `const value_type&`
`pointer`	`allocator_type::pointer`	for the default allocator: `value_type*`
`const_pointer`	`allocator_type::const_pointer`	for the default allocator: `const value_type*`
`iterator`	a bidirectional iterator to `value_type`	convertible to `const_iterator`
`const_iterator`	a bidirectional iterator to `const value_type`
`reverse_iterator`	`reverse_iterator<iterator>`
`const_reverse_iterator`	`reverse_iterator<const_iterator>`
`difference_type`	a signed integral type, identical to: `iterator_traits<iterator>::difference_type`	usually the same as ptrdiff_t
`size_type`	an unsigned integral type that can represent any non-negative value of `difference_type`	usually the same as size_t

member type	definition	notes
`key_type`	The first template parameter (`T`)
`value_type`	The first template parameter (`T`)
`key_compare`	The second template parameter (`Compare`)	defaults to: `less<key_type>`
`value_compare`	The second template parameter (`Compare`)	defaults to: `less<value_type>`
`allocator_type`	The third template parameter (`Alloc`)	defaults to: `allocator<value_type>`
`reference`	`value_type&`
`const_reference`	`const value_type&`
`pointer`	`allocator_traits<allocator_type>::pointer`	for the default allocator: `value_type*`
`const_pointer`	`allocator_traits<allocator_type>::const_pointer`	for the default allocator: `const value_type*`
`iterator`	a bidirectional iterator to `const value_type`	* convertible to `const_iterator`
`const_iterator`	a bidirectional iterator to `const value_type`	*
`reverse_iterator`	`reverse_iterator<iterator>`	*
`const_reverse_iterator`	`reverse_iterator<const_iterator>`	*
`difference_type`	a signed integral type, identical to: `iterator_traits<iterator>::difference_type`	usually the same as ptrdiff_t
`size_type`	an unsigned integral type that can represent any non-negative value of `difference_type`	usually the same as size_t

*Note: All iterators in a multiset point to const elements. Whether the const_ member type is the same type as its non-const_ counterpart depends on the particular library implementation, but programs should not rely on them being different to overload functions: const_iterator is more generic, since iterator is always convertible to it.

Member functions

(constructor): Construct multiset (public member function )

(destructor): Multiset destructor (public member function )

operator=: Copy container content (public member function )

Iterators:

begin: Return iterator to beginning (public member function )

end: Return iterator to end (public member function )

rbegin: Return reverse iterator to reverse beginning (public member function )

rend: Return reverse iterator to reverse end (public member function )

cbegin: Return const_iterator to beginning (public member function )

cend: Return const_iterator to end (public member function )

crbegin: Return const_reverse_iterator to reverse beginning (public member function )

crend: Return const_reverse_iterator to reverse end (public member function )

Capacity:

empty: Test whether container is empty (public member function )

size: Return container size (public member function )

max_size: Return maximum size (public member function )

Modifiers:

insert: Insert element (public member function )

erase: Erase elements (public member function )

swap: Swap content (public member function )

clear: Clear content (public member function )

emplace: Construct and insert element (public member function )

emplace_hint: Construct and insert element with hint (public member function )

Observers:

key_comp: Return comparison object (public member function )

value_comp: Return comparison object (public member function )

Operations:

find: Get iterator to element (public member function )

count: Count elements with a specific key (public member function )

lower_bound: Return iterator to lower bound (public member function )

upper_bound: Return iterator to upper bound (public member function )

equal_range: Get range of equal elements (public member function )

Allocator:

get_allocator: Get allocator (public member function )

multiset
set

std::multiset

Container properties

Template parameters

Member types

Member functions

C++

Reference

C library:

Containers:

Input/Output:

Multi-threading:

Other:

<set>

multiset

member functions:

non-member overloads: