---
name: "std::multiset"
section: "3cxx"
platform: "linux"
package: "libstdc++-12-doc"
version: "12.4.0-5"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/std::multiset/3cxx"
---

# std::multiset(3cxx)

A standard container made up of elements, which can be retrieved in logarithmic time.

## NAME

std::multiset\< \_Key, \_Compare, \_Alloc \> - A standard container made up of elements, which can be retrieved in logarithmic time.

## SYNOPSIS

`#include <set>`

### Public Types

**typedef** \_Alloc **allocator\_type**\
 **typedef** **\_Rep\_type::const\_iterator** **const\_iterator**\
 **typedef** \_Alloc\_traits::const\_pointer **const\_pointer**\
 **typedef** \_Alloc\_traits::const\_reference **const\_reference**\
 **typedef** **\_Rep\_type::const\_reverse\_iterator** **const\_reverse\_iterator**\
 **typedef** \_Rep\_type::difference\_type **difference\_type**\
 **typedef** **\_Rep\_type::const\_iterator** **iterator**\
 **typedef** \_Compare **key\_compare**\
 **typedef** **\_Key** **key\_type**\
 **using** **node\_type** = **typename** **\_Rep\_type::node\_type**\
 **typedef** **\_Alloc\_traits::pointer** **pointer**\
 **typedef** \_Alloc\_traits::reference **reference**\
 **typedef** **\_Rep\_type::const\_reverse\_iterator** **reverse\_iterator**\
 **typedef** \_Rep\_type::size\_type **size\_type**\
 **typedef** \_Compare **value\_compare**\
 **typedef** **\_Key** **value\_type**\

### Public Member Functions

**multiset** ()=**default**\
 Default constructor creates no elements.  template\<**typename** **\_InputIterator** \> **multiset** (**\_InputIterator** \_\_first, **\_InputIterator** \_\_last)\
 Builds a multiset from a range.  template\<**typename** **\_InputIterator** \> **multiset** (**\_InputIterator** \_\_first, **\_InputIterator** \_\_last, const \_Compare &\_\_comp, const allocator\_type &\_\_a=allocator\_type())\
 Builds a multiset from a range.  template\<**typename** **\_InputIterator** \> **multiset** (**\_InputIterator** \_\_first, **\_InputIterator** \_\_last, const allocator\_type &\_\_a)\
 Allocator-extended range constructor.  **multiset** (const \_Compare &\_\_comp, const allocator\_type &\_\_a=allocator\_type())\
 Creates a multiset with no elements.  **multiset** (const allocator\_type &\_\_a)\
 Allocator-extended default constructor.  **multiset** (const **multiset** &)=**default**\
 Multiset copy constructor.  **multiset** (const **multiset** &**\_\_m**, const **\_\_type\_identity\_t**\< allocator\_type \> &\_\_a)\
 Allocator-extended copy constructor.  **multiset** (**initializer\_list**\< **value\_type** \> **\_\_l**, const \_Compare &\_\_comp=\_Compare(), const allocator\_type &\_\_a=allocator\_type())\
 Builds a multiset from an initializer\_list.  **multiset** (**initializer\_list**\< **value\_type** \> **\_\_l**, const allocator\_type &\_\_a)\
 Allocator-extended initialier-list constructor.  **multiset** (**multiset** &&)=**default**\
 Multiset move constructor.  **multiset** (**multiset** &&**\_\_m**, const **\_\_type\_identity\_t**\< allocator\_type \> &\_\_a) noexcept(**is\_nothrow\_copy\_constructible**\< \_Compare \>::value &&\_Alloc\_traits::\_S\_always\_equal())\
 Allocator-extended move constructor.  **~multiset** ()=**default**\
 **iterator** **begin** () const noexcept\
 **iterator** **cbegin** () const noexcept\
 **iterator** **cend** () const noexcept\
 **void** **clear** () noexcept\
 **reverse\_iterator** **crbegin** () const noexcept\
 **reverse\_iterator** **crend** () const noexcept\
 template\<typename... \_Args\> **iterator** **emplace** (**\_Args** &&... **\_\_args**)\
 Builds and inserts an element into the multiset.  template\<typename... \_Args\> **iterator** **emplace\_hint** (**const\_iterator** **\_\_pos**, **\_Args** &&... **\_\_args**)\
 Builds and inserts an element into the multiset.  bool **empty** () const noexcept\
 Returns true if the set is empty.  **iterator** **end** () const noexcept\
 size\_type **erase** (const **key\_type** &\_\_x)\
 Erases elements according to the provided key.  \_GLIBCXX\_ABI\_TAG\_CXX11 **iterator** **erase** (**const\_iterator** \_\_first, **const\_iterator** \_\_last)\
 Erases a \[first,last) range of elements from a multiset.  \_GLIBCXX\_ABI\_TAG\_CXX11 **iterator** **erase** (**const\_iterator** **\_\_position**)\
 Erases an element from a multiset.  node\_type **extract** (const **key\_type** &\_\_x)\
 Extract a node.  node\_type **extract** (**const\_iterator** **\_\_pos**)\
 Extract a node.  allocator\_type **get\_allocator** () const noexcept\
 Returns the memory allocation object.  template\<**typename** **\_InputIterator** \> **void** **insert** (**\_InputIterator** \_\_first, **\_InputIterator** \_\_last)\
 A template function that tries to insert a range of elements.  **iterator** **insert** (const **value\_type** &\_\_x)\
 Inserts an element into the multiset.  **iterator** **insert** (**const\_iterator** **\_\_hint**, node\_type &&**\_\_nh**)\
 Re-insert an extracted node.  **iterator** **insert** (**const\_iterator** **\_\_position**, const **value\_type** &\_\_x)\
 Inserts an element into the multiset.  **iterator** **insert** (**const\_iterator** **\_\_position**, **value\_type** &&\_\_x)\
 **void** **insert** (**initializer\_list**\< **value\_type** \> **\_\_l**)\
 Attempts to insert a list of elements into the multiset.  **iterator** **insert** (node\_type &&**\_\_nh**)\
 Re-insert an extracted node.  **iterator** **insert** (**value\_type** &&\_\_x)\
 key\_compare **key\_comp** () const\
 Returns the comparison object.  size\_type **max\_size** () const noexcept\
 Returns the maximum size of the set.  template\<**typename** **\_Compare1** \> **void** **merge** (**multiset**\< **\_Key**, **\_Compare1**, \_Alloc \> &&**\_\_source**)\
 template\<**typename** **\_Compare1** \> **void** **merge** (**multiset**\< **\_Key**, **\_Compare1**, \_Alloc \> &**\_\_source**)\
 template\<**typename** **\_Compare1** \> **void** **merge** (**set**\< **\_Key**, **\_Compare1**, \_Alloc \> &&**\_\_source**)\
 template\<**typename** **\_Compare1** \> **void** **merge** (**set**\< **\_Key**, **\_Compare1**, \_Alloc \> &**\_\_source**)\
 **multiset** & **operator=** (const **multiset** &)=**default**\
 Multiset assignment operator.  **multiset** & **operator=** (**initializer\_list**\< **value\_type** \> **\_\_l**)\
 Multiset list assignment operator.  **multiset** & **operator=** (**multiset** &&)=**default**\
 Move assignment operator.  **reverse\_iterator** **rbegin** () const noexcept\
 **reverse\_iterator** **rend** () const noexcept\
 size\_type **size** () const noexcept\
 Returns the size of the set.  **void** **swap** (**multiset** &\_\_x) noexcept(/\***conditional** \*/)\
 Swaps data with another multiset.  value\_compare **value\_comp** () const\
 Returns the comparison object.

size\_type **count** (const **key\_type** &\_\_x) const\
 Finds the number of elements with given key.  template\<**typename** **\_Kt** \> **auto** **count** (const **\_Kt** &\_\_x) const -\> **decltype**(\_M\_t.\_M\_count\_tr(\_\_x))\
 Finds the number of elements with given key.

bool **contains** (const **key\_type** &\_\_x) const\
 Finds whether an element with the given key exists.  template\<**typename** **\_Kt** \> **auto** **contains** (const **\_Kt** &\_\_x) const -\> **decltype**(\_M\_t.\_M\_find\_tr(\_\_x), **void**(), **true**)\
 Finds whether an element with the given key exists.

**iterator** **find** (const **key\_type** &\_\_x)\
 Tries to locate an element in a set.  **const\_iterator** **find** (const **key\_type** &\_\_x) const\
 Tries to locate an element in a set.  template\<**typename** **\_Kt** \> **auto** **find** (const **\_Kt** &\_\_x) -\> **decltype**(**iterator**{\_M\_t.\_M\_find\_tr(\_\_x)})\
 Tries to locate an element in a set.  template\<**typename** **\_Kt** \> **auto** **find** (const **\_Kt** &\_\_x) const -\> **decltype**(**const\_iterator**{\_M\_t.\_M\_find\_tr(\_\_x)})\
 Tries to locate an element in a set.

**iterator** **lower\_bound** (const **key\_type** &\_\_x)\
 Finds the beginning of a subsequence matching given key.  **const\_iterator** **lower\_bound** (const **key\_type** &\_\_x) const\
 Finds the beginning of a subsequence matching given key.  template\<**typename** **\_Kt** \> **auto** **lower\_bound** (const **\_Kt** &\_\_x) -\> **decltype**(**iterator**(\_M\_t.\_M\_lower\_bound\_tr(\_\_x)))\
 Finds the beginning of a subsequence matching given key.  template\<**typename** **\_Kt** \> **auto** **lower\_bound** (const **\_Kt** &\_\_x) const -\> **decltype**(**iterator**(\_M\_t.\_M\_lower\_bound\_tr(\_\_x)))\
 Finds the beginning of a subsequence matching given key.

**iterator** **upper\_bound** (const **key\_type** &\_\_x)\
 Finds the end of a subsequence matching given key.  **const\_iterator** **upper\_bound** (const **key\_type** &\_\_x) const\
 Finds the end of a subsequence matching given key.  template\<**typename** **\_Kt** \> **auto** **upper\_bound** (const **\_Kt** &\_\_x) -\> **decltype**(**iterator**(\_M\_t.\_M\_upper\_bound\_tr(\_\_x)))\
 Finds the end of a subsequence matching given key.  template\<**typename** **\_Kt** \> **auto** **upper\_bound** (const **\_Kt** &\_\_x) const -\> **decltype**(**iterator**(\_M\_t.\_M\_upper\_bound\_tr(\_\_x)))\
 Finds the end of a subsequence matching given key.

**std::pair**\< **iterator**, **iterator** \> **equal\_range** (const **key\_type** &\_\_x)\
 Finds a subsequence matching given key.  **std::pair**\< **const\_iterator**, **const\_iterator** \> **equal\_range** (const **key\_type** &\_\_x) const\
 Finds a subsequence matching given key.  template\<**typename** **\_Kt** \> **auto** **equal\_range** (const **\_Kt** &\_\_x) -\> **decltype**(**pair**\< **iterator**, **iterator** \>(\_M\_t.\_M\_equal\_range\_tr(\_\_x)))\
 Finds a subsequence matching given key.  template\<**typename** **\_Kt** \> **auto** **equal\_range** (const **\_Kt** &\_\_x) const -\> **decltype**(**pair**\< **iterator**, **iterator** \>(\_M\_t.\_M\_equal\_range\_tr(\_\_x)))\
 Finds a subsequence matching given key.

### Friends

template\<**typename** **\_K1** , **typename** **\_C1** , **typename** **\_A1** \> bool **operator\<** (const **multiset**\< **\_K1**, **\_C1**, **\_A1** \> &, const **multiset**\< **\_K1**, **\_C1**, **\_A1** \> &)\
 template\<**typename** **\_K1** , **typename** **\_C1** , **typename** **\_A1** \> bool **operator==** (const **multiset**\< **\_K1**, **\_C1**, **\_A1** \> &, const **multiset**\< **\_K1**, **\_C1**, **\_A1** \> &)\
 template\<**typename** , **typename** \> **struct** **std::\_Rb\_tree\_merge\_helper**\

## Detailed Description

### template\<typename \_Key, typename \_Compare = std::less\<\_Key\>, typename \_Alloc = std::allocator\<\_Key\>\>

class std::multiset\< \_Key, \_Compare, \_Alloc \>"A standard container made up of elements, which can be retrieved in logarithmic time.

**Since**

C++98

**Template Parameters**

*\_Key* Type of key objects. \
 *\_Compare* Comparison function object type, defaults to less\<\_Key\>. \
 *\_Alloc* Allocator type, defaults to allocator\<\_Key\>.

Meets the requirements of a `container`, a `reversible container`, and an `associative container` (using equivalent keys). For a `multiset<Key>` the key\_type and value\_type are Key.

Multisets support bidirectional iterators.

The private tree data is declared exactly the same way for set and multiset; the distinction is made entirely in how the tree functions are called (\*\_unique versus \*\_equal, same as the standard).

## Constructor & Destructor Documentation

### template\<typename \_Key , typename \_Compare = std::less\<\_Key\>, typename \_Alloc = std::allocator\<\_Key\>\> std::multiset\< \_Key, \_Compare, \_Alloc \>::multiset ()` [default]`

Default constructor creates no elements.

### template\<typename \_Key , typename \_Compare = std::less\<\_Key\>, typename \_Alloc = std::allocator\<\_Key\>\> std::multiset\< \_Key, \_Compare, \_Alloc \>::multiset (const \_Compare & \_\_comp, const allocator\_type & \_\_a = `allocator_type()`)` [inline]`, ` [explicit]`

Creates a multiset with no elements.

**Parameters**

*\_\_comp* Comparator to use. \
 *\_\_a* An allocator object.

### template\<typename \_Key , typename \_Compare = std::less\<\_Key\>, typename \_Alloc = std::allocator\<\_Key\>\> template\<typename \_InputIterator \> std::multiset\< \_Key, \_Compare, \_Alloc \>::multiset (\_InputIterator \_\_first, \_InputIterator \_\_last)` [inline]`

Builds a multiset from a range.

**Parameters**

*\_\_first* An input iterator. \
 *\_\_last* An input iterator.

Create a multiset consisting of copies of the elements from \[first,last). This is linear in N if the range is already sorted, and NlogN otherwise (where N is distance(\_\_first,\_\_last)).

### template\<typename \_Key , typename \_Compare = std::less\<\_Key\>, typename \_Alloc = std::allocator\<\_Key\>\> template\<typename \_InputIterator \> std::multiset\< \_Key, \_Compare, \_Alloc \>::multiset (\_InputIterator \_\_first, \_InputIterator \_\_last, const \_Compare & \_\_comp, const allocator\_type & \_\_a = `allocator_type()`)` [inline]`

Builds a multiset from a range.

**Parameters**

*\_\_first* An input iterator. \
 *\_\_last* An input iterator. \
 *\_\_comp* A comparison functor. \
 *\_\_a* An allocator object.

Create a multiset consisting of copies of the elements from \[\_\_first,\_\_last). This is linear in N if the range is already sorted, and NlogN otherwise (where N is distance(\_\_first,\_\_last)).

### template\<typename \_Key , typename \_Compare = std::less\<\_Key\>, typename \_Alloc = std::allocator\<\_Key\>\> std::multiset\< \_Key, \_Compare, \_Alloc \>::multiset (const multiset\< \_Key, \_Compare, \_Alloc \> &)` [default]`

Multiset copy constructor. Whether the allocator is copied depends on the allocator traits.

### template\<typename \_Key , typename \_Compare = std::less\<\_Key\>, typename \_Alloc = std::allocator\<\_Key\>\> std::multiset\< \_Key, \_Compare, \_Alloc \>::multiset (multiset\< \_Key, \_Compare, \_Alloc \> &&)` [default]`

Multiset move constructor. The newly-created multiset contains the exact contents of the moved instance. The moved instance is a valid, but unspecified multiset.

### template\<typename \_Key , typename \_Compare = std::less\<\_Key\>, typename \_Alloc = std::allocator\<\_Key\>\> std::multiset\< \_Key, \_Compare, \_Alloc \>::multiset (initializer\_list\< value\_type \> \_\_l, const \_Compare & \_\_comp = `_Compare()`, const allocator\_type & \_\_a = `allocator_type()`)` [inline]`

Builds a multiset from an initializer\_list.

**Parameters**

*\_\_l* An initializer\_list. \
 *\_\_comp* A comparison functor. \
 *\_\_a* An allocator object.

Create a multiset consisting of copies of the elements from the list. This is linear in N if the list is already sorted, and NlogN otherwise (where N is *\_\_l.size()*).

### template\<typename \_Key , typename \_Compare = std::less\<\_Key\>, typename \_Alloc = std::allocator\<\_Key\>\> std::multiset\< \_Key, \_Compare, \_Alloc \>::multiset (const allocator\_type & \_\_a)` [inline]`, ` [explicit]`

Allocator-extended default constructor.

### template\<typename \_Key , typename \_Compare = std::less\<\_Key\>, typename \_Alloc = std::allocator\<\_Key\>\> std::multiset\< \_Key, \_Compare, \_Alloc \>::multiset (const multiset\< \_Key, \_Compare, \_Alloc \> & \_\_m, const \_\_type\_identity\_t\< allocator\_type \> & \_\_a)` [inline]`

Allocator-extended copy constructor.

### template\<typename \_Key , typename \_Compare = std::less\<\_Key\>, typename \_Alloc = std::allocator\<\_Key\>\> std::multiset\< \_Key, \_Compare, \_Alloc \>::multiset (multiset\< \_Key, \_Compare, \_Alloc \> && \_\_m, const \_\_type\_identity\_t\< allocator\_type \> & \_\_a)` [inline]`, ` [noexcept]`

Allocator-extended move constructor.

### template\<typename \_Key , typename \_Compare = std::less\<\_Key\>, typename \_Alloc = std::allocator\<\_Key\>\> std::multiset\< \_Key, \_Compare, \_Alloc \>::multiset (initializer\_list\< value\_type \> \_\_l, const allocator\_type & \_\_a)` [inline]`

Allocator-extended initialier-list constructor.

### template\<typename \_Key , typename \_Compare = std::less\<\_Key\>, typename \_Alloc = std::allocator\<\_Key\>\> template\<typename \_InputIterator \> std::multiset\< \_Key, \_Compare, \_Alloc \>::multiset (\_InputIterator \_\_first, \_InputIterator \_\_last, const allocator\_type & \_\_a)` [inline]`

Allocator-extended range constructor.

### template\<typename \_Key , typename \_Compare = std::less\<\_Key\>, typename \_Alloc = std::allocator\<\_Key\>\> std::multiset\< \_Key, \_Compare, \_Alloc \>::~multiset ()` [default]`

The dtor only erases the elements, and note that if the elements themselves are pointers, the pointed-to memory is not touched in any way. Managing the pointer is the user's responsibility.

## Member Function Documentation

### template\<typename \_Key , typename \_Compare = std::less\<\_Key\>, typename \_Alloc = std::allocator\<\_Key\>\> iterator std::multiset\< \_Key, \_Compare, \_Alloc \>::begin () const` [inline]`, ` [noexcept]`

Returns a read-only (constant) iterator that points to the first element in the multiset. Iteration is done in ascending order according to the keys.

### template\<typename \_Key , typename \_Compare = std::less\<\_Key\>, typename \_Alloc = std::allocator\<\_Key\>\> iterator std::multiset\< \_Key, \_Compare, \_Alloc \>::cbegin () const` [inline]`, ` [noexcept]`

Returns a read-only (constant) iterator that points to the first element in the multiset. Iteration is done in ascending order according to the keys.

### template\<typename \_Key , typename \_Compare = std::less\<\_Key\>, typename \_Alloc = std::allocator\<\_Key\>\> iterator std::multiset\< \_Key, \_Compare, \_Alloc \>::cend () const` [inline]`, ` [noexcept]`

Returns a read-only (constant) iterator that points one past the last element in the multiset. Iteration is done in ascending order according to the keys.

### template\<typename \_Key , typename \_Compare = std::less\<\_Key\>, typename \_Alloc = std::allocator\<\_Key\>\> void std::multiset\< \_Key, \_Compare, \_Alloc \>::clear ()` [inline]`, ` [noexcept]`

Erases all elements in a multiset. Note that this function only erases the elements, and that if the elements themselves are pointers, the pointed-to memory is not touched in any way. Managing the pointer is the user's responsibility.

### template\<typename \_Key , typename \_Compare = std::less\<\_Key\>, typename \_Alloc = std::allocator\<\_Key\>\> template\<typename \_Kt \> auto std::multiset\< \_Key, \_Compare, \_Alloc \>::contains (const \_Kt & \_\_x) const -\> decltype(\_M\_t.\_M\_find\_tr(\_\_x), void(), true)

	` [inline]`"

Finds whether an element with the given key exists.

**Parameters**

*\_\_x* Key of elements to be located.

**Returns**

True if there is any element with the specified key.

### template\<typename \_Key , typename \_Compare = std::less\<\_Key\>, typename \_Alloc = std::allocator\<\_Key\>\> bool std::multiset\< \_Key, \_Compare, \_Alloc \>::contains (const key\_type & \_\_x) const` [inline]`

Finds whether an element with the given key exists.

**Parameters**

*\_\_x* Key of elements to be located.

**Returns**

True if there is any element with the specified key.

### template\<typename \_Key , typename \_Compare = std::less\<\_Key\>, typename \_Alloc = std::allocator\<\_Key\>\> template\<typename \_Kt \> auto std::multiset\< \_Key, \_Compare, \_Alloc \>::count (const \_Kt & \_\_x) const -\> decltype(\_M\_t.\_M\_count\_tr(\_\_x))

	` [inline]`"

Finds the number of elements with given key.

**Parameters**

*\_\_x* Key of elements to be located.

**Returns**

Number of elements with specified key.

### template\<typename \_Key , typename \_Compare = std::less\<\_Key\>, typename \_Alloc = std::allocator\<\_Key\>\> size\_type std::multiset\< \_Key, \_Compare, \_Alloc \>::count (const key\_type & \_\_x) const` [inline]`

Finds the number of elements with given key.

**Parameters**

*\_\_x* Key of elements to be located.

**Returns**

Number of elements with specified key.

### template\<typename \_Key , typename \_Compare = std::less\<\_Key\>, typename \_Alloc = std::allocator\<\_Key\>\> reverse\_iterator std::multiset\< \_Key, \_Compare, \_Alloc \>::crbegin () const` [inline]`, ` [noexcept]`

Returns a read-only (constant) reverse iterator that points to the last element in the multiset. Iteration is done in descending order according to the keys.

### template\<typename \_Key , typename \_Compare = std::less\<\_Key\>, typename \_Alloc = std::allocator\<\_Key\>\> reverse\_iterator std::multiset\< \_Key, \_Compare, \_Alloc \>::crend () const` [inline]`, ` [noexcept]`

Returns a read-only (constant) reverse iterator that points to the last element in the multiset. Iteration is done in descending order according to the keys.

### template\<typename \_Key , typename \_Compare = std::less\<\_Key\>, typename \_Alloc = std::allocator\<\_Key\>\> template\<typename... \_Args\> iterator std::multiset\< \_Key, \_Compare, \_Alloc \>::emplace (\_Args &&... \_\_args)` [inline]`

Builds and inserts an element into the multiset.

**Parameters**

*\_\_args* Arguments used to generate the element instance to be inserted.

**Returns**

An iterator that points to the inserted element.

This function inserts an element into the multiset. Contrary to a std::set the multiset does not rely on unique keys and thus multiple copies of the same element can be inserted.

Insertion requires logarithmic time.

### template\<typename \_Key , typename \_Compare = std::less\<\_Key\>, typename \_Alloc = std::allocator\<\_Key\>\> template\<typename... \_Args\> iterator std::multiset\< \_Key, \_Compare, \_Alloc \>::emplace\_hint (const\_iterator \_\_pos, \_Args &&... \_\_args)` [inline]`

Builds and inserts an element into the multiset.

**Parameters**

*\_\_pos* An iterator that serves as a hint as to where the element should be inserted. \
 *\_\_args* Arguments used to generate the element instance to be inserted.

**Returns**

An iterator that points to the inserted element.

This function inserts an element into the multiset. Contrary to a std::set the multiset does not rely on unique keys and thus multiple copies of the same element can be inserted.

Note that the first parameter is only a hint and can potentially improve the performance of the insertion process. A bad hint would cause no gains in efficiency.

See https://gcc.gnu.org/onlinedocs/libstdc++/manual/associative.html#containers.associative.insert\_hints for more on *hinting*.

Insertion requires logarithmic time (if the hint is not taken).

### template\<typename \_Key , typename \_Compare = std::less\<\_Key\>, typename \_Alloc = std::allocator\<\_Key\>\> bool std::multiset\< \_Key, \_Compare, \_Alloc \>::empty () const` [inline]`, ` [noexcept]`

Returns true if the set is empty.

### template\<typename \_Key , typename \_Compare = std::less\<\_Key\>, typename \_Alloc = std::allocator\<\_Key\>\> iterator std::multiset\< \_Key, \_Compare, \_Alloc \>::end () const` [inline]`, ` [noexcept]`

Returns a read-only (constant) iterator that points one past the last element in the multiset. Iteration is done in ascending order according to the keys.

Referenced by **std::multiset\< \_Key, \_Compare, \_Alloc \>::extract()**.

### template\<typename \_Key , typename \_Compare = std::less\<\_Key\>, typename \_Alloc = std::allocator\<\_Key\>\> template\<typename \_Kt \> auto std::multiset\< \_Key, \_Compare, \_Alloc \>::equal\_range (const \_Kt & \_\_x) -\> decltype(pair\<iterator, iterator\>(\_M\_t.\_M\_equal\_range\_tr(\_\_x)))

	` [inline]`"

Finds a subsequence matching given key.

**Parameters**

*\_\_x* Key to be located.

**Returns**

Pair of iterators that possibly points to the subsequence matching given key.

This function is equivalent to

```
std::make_pair(c.lower_bound(val),
               c.upper_bound(val))
```

 (but is faster than making the calls separately).

This function probably only makes sense for multisets.

### template\<typename \_Key , typename \_Compare = std::less\<\_Key\>, typename \_Alloc = std::allocator\<\_Key\>\> template\<typename \_Kt \> auto std::multiset\< \_Key, \_Compare, \_Alloc \>::equal\_range (const \_Kt & \_\_x) const -\> decltype(pair\<iterator, iterator\>(\_M\_t.\_M\_equal\_range\_tr(\_\_x)))

	` [inline]`"

Finds a subsequence matching given key.

**Parameters**

*\_\_x* Key to be located.

**Returns**

Pair of iterators that possibly points to the subsequence matching given key.

This function is equivalent to

```
std::make_pair(c.lower_bound(val),
               c.upper_bound(val))
```

 (but is faster than making the calls separately).

This function probably only makes sense for multisets.

### template\<typename \_Key , typename \_Compare = std::less\<\_Key\>, typename \_Alloc = std::allocator\<\_Key\>\> std::pair\< iterator, iterator \> std::multiset\< \_Key, \_Compare, \_Alloc \>::equal\_range (const key\_type & \_\_x)` [inline]`

Finds a subsequence matching given key.

**Parameters**

*\_\_x* Key to be located.

**Returns**

Pair of iterators that possibly points to the subsequence matching given key.

This function is equivalent to

```
std::make_pair(c.lower_bound(val),
               c.upper_bound(val))
```

 (but is faster than making the calls separately).

This function probably only makes sense for multisets.

### template\<typename \_Key , typename \_Compare = std::less\<\_Key\>, typename \_Alloc = std::allocator\<\_Key\>\> std::pair\< const\_iterator, const\_iterator \> std::multiset\< \_Key, \_Compare, \_Alloc \>::equal\_range (const key\_type & \_\_x) const` [inline]`

Finds a subsequence matching given key.

**Parameters**

*\_\_x* Key to be located.

**Returns**

Pair of iterators that possibly points to the subsequence matching given key.

This function is equivalent to

```
std::make_pair(c.lower_bound(val),
               c.upper_bound(val))
```

 (but is faster than making the calls separately).

This function probably only makes sense for multisets.

### template\<typename \_Key , typename \_Compare = std::less\<\_Key\>, typename \_Alloc = std::allocator\<\_Key\>\> size\_type std::multiset\< \_Key, \_Compare, \_Alloc \>::erase (const key\_type & \_\_x)` [inline]`

Erases elements according to the provided key.

**Parameters**

*\_\_x* Key of element to be erased.

**Returns**

The number of elements erased.

This function erases all elements located by the given key from a multiset. Note that this function only erases the element, and that if the element is itself a pointer, the pointed-to memory is not touched in any way. Managing the pointer is the user's responsibility.

### template\<typename \_Key , typename \_Compare = std::less\<\_Key\>, typename \_Alloc = std::allocator\<\_Key\>\> \_GLIBCXX\_ABI\_TAG\_CXX11 iterator std::multiset\< \_Key, \_Compare, \_Alloc \>::erase (const\_iterator \_\_first, const\_iterator \_\_last)` [inline]`

Erases a \[first,last) range of elements from a multiset.

**Parameters**

*\_\_first* Iterator pointing to the start of the range to be erased. \
 *\_\_last* Iterator pointing to the end of the range to be erased.

**Returns**

The iterator *last*.

This function erases a sequence of elements from a multiset. Note that this function only erases the elements, and that if the elements themselves are pointers, the pointed-to memory is not touched in any way. Managing the pointer is the user's responsibility.

### template\<typename \_Key , typename \_Compare = std::less\<\_Key\>, typename \_Alloc = std::allocator\<\_Key\>\> \_GLIBCXX\_ABI\_TAG\_CXX11 iterator std::multiset\< \_Key, \_Compare, \_Alloc \>::erase (const\_iterator \_\_position)` [inline]`

Erases an element from a multiset.

**Parameters**

*\_\_position* An iterator pointing to the element to be erased.

**Returns**

An iterator pointing to the element immediately following *position* prior to the element being erased. If no such element exists, end() is returned.

This function erases an element, pointed to by the given iterator, from a multiset. Note that this function only erases the element, and that if the element is itself a pointer, the pointed-to memory is not touched in any way. Managing the pointer is the user's responsibility.

### template\<typename \_Key , typename \_Compare = std::less\<\_Key\>, typename \_Alloc = std::allocator\<\_Key\>\> node\_type std::multiset\< \_Key, \_Compare, \_Alloc \>::extract (const key\_type & \_\_x)` [inline]`

Extract a node.

### template\<typename \_Key , typename \_Compare = std::less\<\_Key\>, typename \_Alloc = std::allocator\<\_Key\>\> node\_type std::multiset\< \_Key, \_Compare, \_Alloc \>::extract (const\_iterator \_\_pos)` [inline]`

Extract a node.

References **std::multiset\< \_Key, \_Compare, \_Alloc \>::end()**.

### template\<typename \_Key , typename \_Compare = std::less\<\_Key\>, typename \_Alloc = std::allocator\<\_Key\>\> template\<typename \_Kt \> auto std::multiset\< \_Key, \_Compare, \_Alloc \>::find (const \_Kt & \_\_x) -\> decltype(iterator{\_M\_t.\_M\_find\_tr(\_\_x)})

	` [inline]`"

Tries to locate an element in a set.

**Parameters**

*\_\_x* Element to be located.

**Returns**

Iterator pointing to sought-after element, or end() if not found.

This function takes a key and tries to locate the element with which the key matches. If successful the function returns an iterator pointing to the sought after element. If unsuccessful it returns the past-the-end ( `end()` ) iterator.

### template\<typename \_Key , typename \_Compare = std::less\<\_Key\>, typename \_Alloc = std::allocator\<\_Key\>\> template\<typename \_Kt \> auto std::multiset\< \_Key, \_Compare, \_Alloc \>::find (const \_Kt & \_\_x) const -\> decltype(const\_iterator{\_M\_t.\_M\_find\_tr(\_\_x)})

	` [inline]`"

Tries to locate an element in a set.

**Parameters**

*\_\_x* Element to be located.

**Returns**

Iterator pointing to sought-after element, or end() if not found.

This function takes a key and tries to locate the element with which the key matches. If successful the function returns an iterator pointing to the sought after element. If unsuccessful it returns the past-the-end ( `end()` ) iterator.

### template\<typename \_Key , typename \_Compare = std::less\<\_Key\>, typename \_Alloc = std::allocator\<\_Key\>\> iterator std::multiset\< \_Key, \_Compare, \_Alloc \>::find (const key\_type & \_\_x)` [inline]`

Tries to locate an element in a set.

**Parameters**

*\_\_x* Element to be located.

**Returns**

Iterator pointing to sought-after element, or end() if not found.

This function takes a key and tries to locate the element with which the key matches. If successful the function returns an iterator pointing to the sought after element. If unsuccessful it returns the past-the-end ( `end()` ) iterator.

### template\<typename \_Key , typename \_Compare = std::less\<\_Key\>, typename \_Alloc = std::allocator\<\_Key\>\> const\_iterator std::multiset\< \_Key, \_Compare, \_Alloc \>::find (const key\_type & \_\_x) const` [inline]`

Tries to locate an element in a set.

**Parameters**

*\_\_x* Element to be located.

**Returns**

Iterator pointing to sought-after element, or end() if not found.

This function takes a key and tries to locate the element with which the key matches. If successful the function returns an iterator pointing to the sought after element. If unsuccessful it returns the past-the-end ( `end()` ) iterator.

### template\<typename \_Key , typename \_Compare = std::less\<\_Key\>, typename \_Alloc = std::allocator\<\_Key\>\> allocator\_type std::multiset\< \_Key, \_Compare, \_Alloc \>::get\_allocator () const` [inline]`, ` [noexcept]`

Returns the memory allocation object.

### template\<typename \_Key , typename \_Compare = std::less\<\_Key\>, typename \_Alloc = std::allocator\<\_Key\>\> template\<typename \_InputIterator \> void std::multiset\< \_Key, \_Compare, \_Alloc \>::insert (\_InputIterator \_\_first, \_InputIterator \_\_last)` [inline]`

A template function that tries to insert a range of elements.

**Parameters**

*\_\_first* Iterator pointing to the start of the range to be inserted. \
 *\_\_last* Iterator pointing to the end of the range.

Complexity similar to that of the range constructor.

### template\<typename \_Key , typename \_Compare = std::less\<\_Key\>, typename \_Alloc = std::allocator\<\_Key\>\> iterator std::multiset\< \_Key, \_Compare, \_Alloc \>::insert (const value\_type & \_\_x)` [inline]`

Inserts an element into the multiset.

**Parameters**

*\_\_x* Element to be inserted.

**Returns**

An iterator that points to the inserted element.

This function inserts an element into the multiset. Contrary to a std::set the multiset does not rely on unique keys and thus multiple copies of the same element can be inserted.

Insertion requires logarithmic time.

Referenced by **std::multiset\< \_Key, \_Compare, \_Alloc \>::insert()**.

### template\<typename \_Key , typename \_Compare = std::less\<\_Key\>, typename \_Alloc = std::allocator\<\_Key\>\> iterator std::multiset\< \_Key, \_Compare, \_Alloc \>::insert (const\_iterator \_\_hint, node\_type && \_\_nh)` [inline]`

Re-insert an extracted node.

References **std::move()**.

### template\<typename \_Key , typename \_Compare = std::less\<\_Key\>, typename \_Alloc = std::allocator\<\_Key\>\> iterator std::multiset\< \_Key, \_Compare, \_Alloc \>::insert (const\_iterator \_\_position, const value\_type & \_\_x)` [inline]`

Inserts an element into the multiset.

**Parameters**

*\_\_position* An iterator that serves as a hint as to where the element should be inserted. \
 *\_\_x* Element to be inserted.

**Returns**

An iterator that points to the inserted element.

This function inserts an element into the multiset. Contrary to a std::set the multiset does not rely on unique keys and thus multiple copies of the same element can be inserted.

Note that the first parameter is only a hint and can potentially improve the performance of the insertion process. A bad hint would cause no gains in efficiency.

See https://gcc.gnu.org/onlinedocs/libstdc++/manual/associative.html#containers.associative.insert\_hints for more on *hinting*.

Insertion requires logarithmic time (if the hint is not taken).

### template\<typename \_Key , typename \_Compare = std::less\<\_Key\>, typename \_Alloc = std::allocator\<\_Key\>\> void std::multiset\< \_Key, \_Compare, \_Alloc \>::insert (initializer\_list\< value\_type \> \_\_l)` [inline]`

Attempts to insert a list of elements into the multiset.

**Parameters**

*\_\_l* A std::initializer\_list\<value\_type\> of elements to be inserted.

Complexity similar to that of the range constructor.

References **std::multiset\< \_Key, \_Compare, \_Alloc \>::insert()**.

### template\<typename \_Key , typename \_Compare = std::less\<\_Key\>, typename \_Alloc = std::allocator\<\_Key\>\> iterator std::multiset\< \_Key, \_Compare, \_Alloc \>::insert (node\_type && \_\_nh)` [inline]`

Re-insert an extracted node.

References **std::move()**.

### template\<typename \_Key , typename \_Compare = std::less\<\_Key\>, typename \_Alloc = std::allocator\<\_Key\>\> key\_compare std::multiset\< \_Key, \_Compare, \_Alloc \>::key\_comp () const` [inline]`

Returns the comparison object.

### template\<typename \_Key , typename \_Compare = std::less\<\_Key\>, typename \_Alloc = std::allocator\<\_Key\>\> template\<typename \_Kt \> auto std::multiset\< \_Key, \_Compare, \_Alloc \>::lower\_bound (const \_Kt & \_\_x) -\> decltype(iterator(\_M\_t.\_M\_lower\_bound\_tr(\_\_x)))

	` [inline]`"

Finds the beginning of a subsequence matching given key.

**Parameters**

*\_\_x* Key to be located.

**Returns**

Iterator pointing to first element equal to or greater than key, or end().

This function returns the first element of a subsequence of elements that matches the given key. If unsuccessful it returns an iterator pointing to the first element that has a greater value than given key or end() if no such element exists.

### template\<typename \_Key , typename \_Compare = std::less\<\_Key\>, typename \_Alloc = std::allocator\<\_Key\>\> template\<typename \_Kt \> auto std::multiset\< \_Key, \_Compare, \_Alloc \>::lower\_bound (const \_Kt & \_\_x) const -\> decltype(iterator(\_M\_t.\_M\_lower\_bound\_tr(\_\_x)))

	` [inline]`"

Finds the beginning of a subsequence matching given key.

**Parameters**

*\_\_x* Key to be located.

**Returns**

Iterator pointing to first element equal to or greater than key, or end().

This function returns the first element of a subsequence of elements that matches the given key. If unsuccessful it returns an iterator pointing to the first element that has a greater value than given key or end() if no such element exists.

### template\<typename \_Key , typename \_Compare = std::less\<\_Key\>, typename \_Alloc = std::allocator\<\_Key\>\> iterator std::multiset\< \_Key, \_Compare, \_Alloc \>::lower\_bound (const key\_type & \_\_x)` [inline]`

Finds the beginning of a subsequence matching given key.

**Parameters**

*\_\_x* Key to be located.

**Returns**

Iterator pointing to first element equal to or greater than key, or end().

This function returns the first element of a subsequence of elements that matches the given key. If unsuccessful it returns an iterator pointing to the first element that has a greater value than given key or end() if no such element exists.

### template\<typename \_Key , typename \_Compare = std::less\<\_Key\>, typename \_Alloc = std::allocator\<\_Key\>\> const\_iterator std::multiset\< \_Key, \_Compare, \_Alloc \>::lower\_bound (const key\_type & \_\_x) const` [inline]`

Finds the beginning of a subsequence matching given key.

**Parameters**

*\_\_x* Key to be located.

**Returns**

Iterator pointing to first element equal to or greater than key, or end().

This function returns the first element of a subsequence of elements that matches the given key. If unsuccessful it returns an iterator pointing to the first element that has a greater value than given key or end() if no such element exists.

### template\<typename \_Key , typename \_Compare = std::less\<\_Key\>, typename \_Alloc = std::allocator\<\_Key\>\> size\_type std::multiset\< \_Key, \_Compare, \_Alloc \>::max\_size () const` [inline]`, ` [noexcept]`

Returns the maximum size of the set.

### template\<typename \_Key , typename \_Compare = std::less\<\_Key\>, typename \_Alloc = std::allocator\<\_Key\>\> multiset & std::multiset\< \_Key, \_Compare, \_Alloc \>::operator= (const multiset\< \_Key, \_Compare, \_Alloc \> &)` [default]`

Multiset assignment operator. Whether the allocator is copied depends on the allocator traits.

### template\<typename \_Key , typename \_Compare = std::less\<\_Key\>, typename \_Alloc = std::allocator\<\_Key\>\> multiset & std::multiset\< \_Key, \_Compare, \_Alloc \>::operator= (initializer\_list\< value\_type \> \_\_l)` [inline]`

Multiset list assignment operator.

**Parameters**

*\_\_l* An initializer\_list.

This function fills a multiset with copies of the elements in the initializer list *\_\_l*.

Note that the assignment completely changes the multiset and that the resulting multiset's size is the same as the number of elements assigned.

### template\<typename \_Key , typename \_Compare = std::less\<\_Key\>, typename \_Alloc = std::allocator\<\_Key\>\> multiset & std::multiset\< \_Key, \_Compare, \_Alloc \>::operator= (multiset\< \_Key, \_Compare, \_Alloc \> &&)` [default]`

Move assignment operator.

### template\<typename \_Key , typename \_Compare = std::less\<\_Key\>, typename \_Alloc = std::allocator\<\_Key\>\> reverse\_iterator std::multiset\< \_Key, \_Compare, \_Alloc \>::rbegin () const` [inline]`, ` [noexcept]`

Returns a read-only (constant) reverse iterator that points to the last element in the multiset. Iteration is done in descending order according to the keys.

### template\<typename \_Key , typename \_Compare = std::less\<\_Key\>, typename \_Alloc = std::allocator\<\_Key\>\> reverse\_iterator std::multiset\< \_Key, \_Compare, \_Alloc \>::rend () const` [inline]`, ` [noexcept]`

Returns a read-only (constant) reverse iterator that points to the last element in the multiset. Iteration is done in descending order according to the keys.

### template\<typename \_Key , typename \_Compare = std::less\<\_Key\>, typename \_Alloc = std::allocator\<\_Key\>\> size\_type std::multiset\< \_Key, \_Compare, \_Alloc \>::size () const` [inline]`, ` [noexcept]`

Returns the size of the set.

### template\<typename \_Key , typename \_Compare = std::less\<\_Key\>, typename \_Alloc = std::allocator\<\_Key\>\> void std::multiset\< \_Key, \_Compare, \_Alloc \>::swap (multiset\< \_Key, \_Compare, \_Alloc \> & \_\_x)` [inline]`, ` [noexcept]`

Swaps data with another multiset.

**Parameters**

*\_\_x* A multiset of the same element and allocator types.

This exchanges the elements between two multisets in constant time. (It is only swapping a pointer, an integer, and an instance of the `Compare` type (which itself is often stateless and empty), so it should be quite fast.) Note that the global std::swap() function is specialized such that std::swap(s1,s2) will feed to this function.

Whether the allocators are swapped depends on the allocator traits.

### template\<typename \_Key , typename \_Compare = std::less\<\_Key\>, typename \_Alloc = std::allocator\<\_Key\>\> template\<typename \_Kt \> auto std::multiset\< \_Key, \_Compare, \_Alloc \>::upper\_bound (const \_Kt & \_\_x) -\> decltype(iterator(\_M\_t.\_M\_upper\_bound\_tr(\_\_x)))

	` [inline]`"

Finds the end of a subsequence matching given key.

**Parameters**

*\_\_x* Key to be located.

**Returns**

Iterator pointing to the first element greater than key, or end().

### template\<typename \_Key , typename \_Compare = std::less\<\_Key\>, typename \_Alloc = std::allocator\<\_Key\>\> template\<typename \_Kt \> auto std::multiset\< \_Key, \_Compare, \_Alloc \>::upper\_bound (const \_Kt & \_\_x) const -\> decltype(iterator(\_M\_t.\_M\_upper\_bound\_tr(\_\_x)))

	` [inline]`"

Finds the end of a subsequence matching given key.

**Parameters**

*\_\_x* Key to be located.

**Returns**

Iterator pointing to the first element greater than key, or end().

### template\<typename \_Key , typename \_Compare = std::less\<\_Key\>, typename \_Alloc = std::allocator\<\_Key\>\> iterator std::multiset\< \_Key, \_Compare, \_Alloc \>::upper\_bound (const key\_type & \_\_x)` [inline]`

Finds the end of a subsequence matching given key.

**Parameters**

*\_\_x* Key to be located.

**Returns**

Iterator pointing to the first element greater than key, or end().

### template\<typename \_Key , typename \_Compare = std::less\<\_Key\>, typename \_Alloc = std::allocator\<\_Key\>\> const\_iterator std::multiset\< \_Key, \_Compare, \_Alloc \>::upper\_bound (const key\_type & \_\_x) const` [inline]`

Finds the end of a subsequence matching given key.

**Parameters**

*\_\_x* Key to be located.

**Returns**

Iterator pointing to the first element greater than key, or end().

### template\<typename \_Key , typename \_Compare = std::less\<\_Key\>, typename \_Alloc = std::allocator\<\_Key\>\> value\_compare std::multiset\< \_Key, \_Compare, \_Alloc \>::value\_comp () const` [inline]`

Returns the comparison object.

## Author

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