`<hash_map>`

Include the STL
standard header ** <hash_map>** to define the
container
template classes

`hash_map`

and
`hash_multimap`

, and their supporting
templates.namespace std { template<class Key, class Pr> classhash_compare; template<class Key, class Ty, class Tr, class Alloc> classhash_map; template<class Key, class Ty, class Tr, class Alloc> classhash_multimap; // TEMPLATE FUNCTIONS template<class Key, class Ty, class Tr, class Alloc> booloperator==( const hash_map<Key, Ty, Tr, Alloc>& left, const hash_map<Key, Ty, Tr, Alloc>& right); template<class Key, class Ty, class Tr, class Alloc> booloperator==( const hash_multimap<Key, Ty, Tr, Alloc>& left, const hash_multimap<Key, Ty, Tr, Alloc>& right); template<class Key, class Ty, class Tr, class Alloc> booloperator!=( const hash_map<Key, Ty, Tr, Alloc>& left, const hash_map<Key, Ty, Tr, Alloc>& right); template<class Key, class Ty, class Tr, class Alloc> booloperator!=( const hash_multimap<Key, Ty, Tr, Alloc>& left, const hash_multimap<Key, Ty, Tr, Alloc>& right); template<class Key, class Ty, class Tr, class Alloc> booloperator<( const hash_map<Key, Ty, Tr, Alloc>& left, const hash_map<Key, Ty, Tr, Alloc>& right); template<class Key, class Ty, class Tr, class Alloc> booloperator<( const hash_multimap<Key, Ty, Tr, Alloc>& left, const hash_multimap<Key, Ty, Tr, Alloc>& right); template<class Key, class Ty, class Tr, class Alloc> booloperator>( const hash_map<Key, Ty, Tr, Alloc>& left, const hash_map<Key, Ty, Tr, Alloc>& right); template<class Key, class Ty, class Tr, class Alloc> booloperator>( const hash_multimap<Key, Ty, Tr, Alloc>& left, const hash_multimap<Key, Ty, Tr, Alloc>& right); template<class Key, class Ty, class Tr, class Alloc> booloperator<=( const hash_map<Key, Ty, Tr, Alloc>& left, const hash_map<Key, Ty, Tr, Alloc>& right); template<class Key, class Ty, class Tr, class Alloc> booloperator<=( const hash_multimap<Key, Ty, Tr, Alloc>& left, const hash_multimap<Key, Ty, Tr, Alloc>& right); template<class Key, class Ty, class Tr, class Alloc> booloperator>=( const hash_map<Key, Ty, Tr, Alloc>& left, const hash_map<Key, Ty, Tr, Alloc>& right); template<class Key, class Ty, class Tr, class Alloc> booloperator>=( const hash_multimap<Key, Ty, Tr, Alloc>& left, const hash_multimap<Key, Ty, Tr, Alloc>& right); template<class Key, class Ty, class Tr, class Alloc> voidswap( hash_map<Key, Ty, Tr, Alloc>& left, hash_map<Key, Ty, Tr, Alloc>& right); template<class Key, class Ty, class Tr, class Alloc> voidswap( hash_multimap<Key, Ty, Tr, Alloc>& left, hash_multimap<Key, Ty, Tr, Alloc>& right); } // namespace std

`hash_compare`

template<class Key, class Pr = less<Key> > classhash_compare{ Prcomp; public: const size_tbucket_size= 4; const size_tmin_buckets= 8;hash_compare();hash_compare(Pr pred); size_toperator()(const Key& Key) const; booloperator()(const Key& keyval1, const Key& keyval2) const; };

The template class describes an object that can be used by
any of the containers
`hash_map`

,
`hash_multimap`

,
`hash_set`

, or
`hash_multiset`

as a
**hash traits** object
to order the sequence it controls.
Each of these stores hash traits object of type `Tr`

(a template parameter). You can derive a class from a specialization of
`hash_compare`

, to selectively override certain functions
and objects. Or you can supply your own version of this class,
provided you meet certain minimum requirements.
Specifically, for an object `hash_comp`

of type
`hash_compare<Key, Pr>`

,
the following behavior is required by the above containers:

- For all values
`keyval`

of type`Key`

, the call`hash_comp(keyval)`

serves as a**hash function**, which yields a distribution of values of type`size_t`

. The function supplied by`hash_compare`

simply returns`keyval`

. - For any value
`keyval1`

of type`Key`

that precedes`keyval2`

in the sequence and has the same hash value (value returned by the hash function),`hash_comp(keyval2, keyval1)`

is false. The function must impose a strict weak ordering on values of type`Key`

. The function supplied by`hash_compare`

returns`comp(keyval1, keyval2)`

where`comp`

is a stored object of type`Tr`

that you can specify when you construct the object`hash_comp`

. For the default`Pr`

parameter type`less<Key>`

, sort keys never decrease in value. - The integer constant
`bucket_size`

specifies the mean number of elements per ``bucket'' (hash-table entry) that the container should endeavor not to exceed. It must be greater than zero. The value supplied by`hash_compare`

is 4. - The integer constant
`min_buckets`

specifies the minimum number of buckets to maintain in the hash table. It must be a power of two and greater than zero. The value supplied by`hash_compare`

is 8.

`hash_map`

```
allocator_type
· begin
· bucket
· bucket_count
· bucket_size
· clear
· const_iterator
· const_local_iterator
· const_pointer
· const_reference
· const_reverse_iterator
· count
· difference_type
· empty
· end
· equal_range
· erase
· find
· get_allocator
· insert
· iterator
· key_comp
· key_compare
· key_type
· load_factor
· local_iterator
· lower_bound
· mapped_type
· max_bucket_count
· max_load_factor
· max_size
· operator[]
· hash_map
· rbegin
· reference
· rehash
· rend
· reverse_iterator
· size
· size_type
· swap
· upper_bound
· value_comp
· value_compare
· value_type
```

template<class Key, class Ty, class Tr = hash_compare<Key, less<Key> >, class Alloc = allocator<pair<const Key, Ty> > > classhash_map{ public: typedef Keykey_type; typedef Tymapped_type; typedef Trkey_compare; typedef Allocallocator_type; typedef pair<const Key, Ty>value_type; classvalue_compare; typedef Alloc::pointerpointer; typedef Alloc::const_pointerconst_pointer; typedef Alloc::referencereference; typedef Alloc::const_referenceconst_reference; typedef T0iterator; typedef T1const_iterator; typedef T2size_type; typedef T3difference_type; typedef T4local_iterator; typedef T5const_local_iterator; typedef reverse_iterator<const_iterator>const_reverse_iterator; typedef reverse_iterator<iterator>reverse_iterator;hash_map(); explicithash_map(const Tr& traits);hash_map(const Tr& traits, const Alloc& al);hash_map(const hash_map& right); template<class InIt>hash_map(InIt first, InIt last); template<class InIt>hash_map(InIt first, InIt last, const Tr& traits); template<class InIt>hash_map(InIt first, InIt last, const Tr& traits, const Alloc& al); iteratorbegin(); const_iteratorbegin() const; local_iteratorbegin(size_type nbucket); const_local_iteratorbegin(size_type nbucket) const; iteratorend(); const_iteratorend() const; local_iteratorend(size_type nbucket); const_local_iteratorend(size_type nbucket) const; reverse_iteratorrbegin(); const_reverse_iteratorrbegin() const; reverse_iteratorrend(); const_reverse_iteratorrend() const; size_typesize() const; size_typemax_size() const; boolempty() const; size_typebucket_count() const; size_typemax_bucket_count() const; size_typebucket(const Key& keyval) const; size_typebucket_size(size_type nbucket) const; key_comparekey_comp() const; value_comparevalue_comp() const; Allocget_allocator() const; floatload_factor() const; floatmax_load_factor() const; voidmax_load_factor(float factor); voidrehash(size_type nbuckets); mapped_type&operator[](const Key& keyval); iteratorinsert(const value_type& val); iteratorinsert(iterator where, const value_type& val); template<class InIt> voidinsert(InIt first, InIt last); iteratorerase(iterator where); iteratorerase(iterator first, iterator last); size_typeerase(const Key& keyval); voidclear(); voidswap(hash_map& right); iteratorfind(const Key& keyval); const_iteratorfind(const Key& keyval) const; size_typecount(const Key& keyval) const; iteratorlower_bound(const Key& keyval); const_iteratorlower_bound(const Key& keyval) const; iteratorupper_bound(const Key& keyval); const_iteratorupper_bound(const Key& keyval) const; pair<iterator, iterator>equal_range(const Key& keyval); pair<const_iterator, const_iterator>equal_range(const Key& keyval) const; };

The template class describes an object that controls a
varying-length sequence of elements of type
`pair<const Key, Ty>`

.
The sequence is
ordered by the
hash traits object
`Tr`

, which includes two functions:

- a one-operand
**hash function**, which partitions the sequence into an ordered set of subsequences called**buckets**. -
a two-operand
**comparison function**for imposing a strict weak ordering within each bucket.

Each element stores two objects, a **sort key** and a **value**.
The sequence is represented in a way that permits lookup, insertion,
and removal of an arbitrary element with a number of operations that can be
independent of the number of elements in the sequence (constant time),
at least when all buckets are of roughly equal length.
In the worst case, when all of the elements are in one bucket,
the number of operations is proportional to the number of elements
in the sequence (linear time). Moreover, inserting an element
invalidates no iterators, and removing an element
invalidates only those iterators which point at the removed element.

The object orders the sequence it controls by calling a stored
hash traits object of type `Tr`

.
You access this stored object by calling the member function
`key_comp()`

.
Such a traits object must behave the same as an object of class
`hash_compare<Key, Pr>`

.
Specifically, for all values `keyval`

of type `Key`

,
the call `key_comp()(keyval)`

yields a distribution
of values of type `size_t`

.
Moreover, class `Tr`

imposes a
strict weak ordering
on sort keys of type `Key`

.
For any element `X`

that precedes
`Y`

in the sequence and has the same hash value,
```
key_comp()(Y.first,
X.first)
```

is false. (For the default function object
`less<Key>`

,
sort keys never decrease in value.)
Unlike template class `hash_multimap`

,
an object of template class `hash_map`

does not ensure that
`key_comp()(X.first, Y.first)`

is true.
(Keys need not be unique.)

The object also stores a **maximum load factor**, which specifies the
maximum desired average number of elements per bucket. If inserting an element
causes `load_factor()`

to exceed the maximum load factor, the container increases the number of
buckets and rebuilds the hash table as needed.

The actual order of elements in the controlled sequence depends on the hash function, the comparison function, the order of insertion, the maximum load factor, and the current number of buckets. You cannot in general predict the order of elements in the controlled sequence. You can always be assured, however, that any subset of elements that have equivalent ordering are adjacent in the controlled sequence.

The object allocates and frees storage for the sequence it controls
through a stored allocator object
of class `Alloc`

. Such an allocator object must have
the same external interface as an object of template class
`allocator`

.
Note that the stored allocator object is *not* copied when the container
object is assigned.

`hash_map::allocator_type`

typedef Allocallocator_type;

The type is a synonym for the template parameter `Alloc`

.

`hash_map::begin`

iteratorbegin(); const_iteratorbegin() const; local_iteratorbegin(size_type nbucket); const_local_iteratorbegin(size_type nbucket) const;

The first two member functions return a forward iterator that points at
the first element of the sequence (or just beyond the end of an empty
sequence). The last two member functions return a forward iterator that points at
the first element of bucket `nbucket`

(or just beyond the end of an empty
bucket).

`hash_map::bucket`

size_typebucket(const Key& keyval) const;

The member function returns the bucket number currently corresponding
to the key value `keyval`

.

`hash_map::bucket_count`

size_typebucket_count() const;

The member function returns the current number of buckets.

`hash_map::bucket_size`

size_typebucket_size(size_type nbucket) const;

The member functions returns the size of bucket number `nbucket`

.

`hash_map::clear`

voidclear();

The member function calls
```
erase(
begin(),
end())
```

.

`hash_map::const_iterator`

typedef T1const_iterator;

The type describes an object that can serve as a constant
bidirectional iterator for the controlled sequence.
It is described here as a
synonym for the implementation-defined type `T1`

.

`hash_map::const_local_iterator`

typedef T5const_local_iterator;

The type describes an object that can serve as a constant
forward iterator for a bucket.
It is described here as a
synonym for the implementation-defined type `T5`

.

`hash_map::const_pointer`

typedef Alloc::const_pointerconst_pointer;

The type describes an object that can serve as a constant pointer to an element of the controlled sequence.

`hash_map::const_reference`

typedef Alloc::const_referenceconst_reference;

The type describes an object that can serve as a constant reference to an element of the controlled sequence.

`hash_map::const_reverse_iterator`

typedef reverse_iterator<const_iterator>const_reverse_iterator;

The type describes an object that can serve as a constant reverse bidirectional iterator for the controlled sequence.

`hash_map::count`

size_typecount(const Key& keyval) const;

The member function returns the number of elements in the range
```
[lower_bound(keyval),
upper_bound(keyval)).
```

`hash_map::difference_type`

typedef T3difference_type;

The signed integer type describes an object that can represent the
difference between the addresses of any two elements in the controlled
sequence. It is described here as a
synonym for the implementation-defined type `T3`

.

`hash_map::empty`

boolempty() const;

The member function returns true for an empty controlled sequence.

`hash_map::end`

iteratorend(); const_iteratorend() const; local_iteratorend(size_type nbucket); const_local_iteratorend(size_type nbucket) const;

The first two member functions return a forward iterator that points
just beyond the end of the sequence.
The last two member functions return a forward iterator that points
just beyond the end of bucket `nbucket`

.

`hash_map::equal_range`

pair<iterator, iterator>equal_range(const Key& keyval); pair<const_iterator, const_iterator>equal_range(const Key& keyval) const;

The member function returns a pair of iterators `X`

such that ```
X.first ==
lower_bound(keyval)
```

and ```
X.second ==
upper_bound(keyval)
```

.

`hash_map::erase`

iteratorerase(iterator where); iteratorerase(iterator first, iterator last); size_typeerase(const Key& keyval);

The first member function removes the element of the controlled
sequence pointed to by `where`

.
The second member function removes the elements
in the range `[first, last)`

.
Both return an iterator that designates the first element remaining
beyond any elements removed, or
`end()`

if no such element exists.

The third member removes
the elements with sort keys in the range
```
[lower_bound(keyval),
upper_bound(keyval)).
```

It returns the number of elements it removes.

The member functions never throw an exception.

`hash_map::find`

iteratorfind(const Key& keyval); const_iteratorfind(const Key& keyval) const;

The member function returns
`lower_bound(keyval)`

.

`hash_map::get_allocator`

Allocget_allocator() const;

The member function returns the stored allocator object.

`hash_map::hash_map`

hash_map(); explicithash_map(const Tr& traits);hash_map(const Tr& traits, const Alloc& al);hash_map(const hash_map& right); template<class InIt>hash_map(InIt first, InIt last); template<class InIt>hash_map(InIt first, InIt last, const Tr& traits); template<class InIt>hash_map(InIt first, InIt last, const Tr& traits, const Alloc& al);

All constructors store an
allocator object and
initialize the controlled sequence. The allocator object is the argument
`al`

, if present. For the copy constructor, it is
`right.get_allocator()`

.
Otherwise, it is `Alloc()`

.

All constructors also store a
hash traits object that can later
be returned by calling
`key_comp()`

.
The hash traits object is the argument `traits`

, if present.
For the copy constructor, it is
`right.key_comp()`

).
Otherwise, it is `Tr()`

.

The first three constructors specify an
empty initial controlled sequence. The fourth constructor specifies
a copy of the sequence controlled by `right`

.
The last three constructors specify the sequence of element values
`[first, last)`

.

`hash_map::insert`

iteratorinsert(const value_type& val); iteratorinsert(iterator where, const value_type& val); template<class InIt> voidinsert(InIt first, InIt last);

The first member function inserts the element `val`

in the controlled sequence, then returns
the iterator that designates the inserted element.
The second member function returns `insert(val)`

,
using `where`

as a starting place within the controlled
sequence to search for the insertion point. (Insertion can
possibly occur somewhat faster, if the
insertion point immediately precedes or follows `where`

.)
The third member function
inserts the sequence of element values,
for each `where`

in the range `[first, last)`

,
by calling `insert(*where)`

.

If an exception is thrown during the insertion of a single element, the container is left unaltered and the exception is rethrown. If an exception is thrown during the insertion of multiple elements, the container is left in a stable but unspecified state and the exception is rethrown.

`hash_map::iterator`

typedef T0iterator;

The type describes an object that can serve as a bidirectional
iterator for the controlled sequence.
It is described here as a
synonym for the implementation-defined type `T0`

.

`hash_map::key_comp`

key_comparekey_comp() const;

The member function returns the stored hash traits object that determines the order of elements in the controlled sequence. In particular, the stored object defines the member function:

bool operator()(const Key& left, const Key& right);

which returns true if `left`

strictly
precedes `right`

in the sort order.

`hash_map::key_compare`

typedef Trkey_compare;

The type describes a traits object that behaves much like an object of class
`hash_compare<Key, Pr>`

.
In particular, it can compare two
sort keys to determine the relative order of two
elements in the controlled sequence.

`hash_map::key_type`

typedef Keykey_type;

The type describes the sort key object stored in each element of the controlled sequence.

`hash_map::load_factor`

floatload_factor() const;

The member function returns
```
(float)size() /
(float)bucket_count()
```

,
the average number of elements per bucket.

`hash_map::local_iterator`

typedef T4local_iterator;

The type describes an object that can serve as a
forward iterator for a bucket.
It is described here as a
synonym for the implementation-defined type `T4`

.

`hash_map::lower_bound`

iteratorlower_bound(const Key& keyval); const_iteratorlower_bound(const Key& keyval) const;

The member function returns an iterator that designates the
earliest element `X`

in the controlled sequence for which
```
key_comp()(X.
first, keyval)
```

is
false.

`end()`

.
`hash_map::mapped_type`

typedef Tymapped_type;

The type is a synonym for the template parameter `Ty`

.

`hash_map::max_bucket_count`

size_typemax_bucket_count() const;

The member function returns the maximum number of buckets currently permitted.

`hash_map::max_load_factort`

floatmax_load_factor() const; voidmax_load_factor(float factor);

The first member function returns the stored maximum load factor.
The second member function replaces the stored maximum load factor with `factor`

.

`hash_map::max_size`

size_typemax_size() const;

The member function returns the length of the longest sequence that the object can control.

`hash_map::operator[]`

mapped_type&operator[](const Key& keyval);

The member function determines the iterator `where`

as the return value of
```
insert(
value_type(keyval, Ty())
```

.
(It inserts an element with the specified key if no such element
exists.) It then returns a reference to
`(*where).second`

.

`hash_map::pointer`

typedef Alloc::pointerpointer;

The type describes an object that can serve as a pointer to an element of the controlled sequence.

`hash_map::rbegin`

const_reverse_iteratorrbegin() const; reverse_iteratorrbegin();

The member function returns a reverse bidirectional iterator that points just beyond the end of the controlled sequence. Hence, it designates the beginning of the reverse sequence.

`hash_map::reference`

typedef Alloc::referencereference;

The type describes an object that can serve as a reference to an element of the controlled sequence.

`hash_map::rehash`

voidrehash(size_type nbuckets);

The member function alters the number of buckets to be at least `nbuckets`

and rebuilds the hash table as needed.

`hash_map::rend`

const_reverse_iteratorrend() const; reverse_iteratorrend();

The member function returns a reverse bidirectional iterator that points at the first element of the sequence (or just beyond the end of an empty sequence). Hence, it designates the end of the reverse sequence.

`hash_map::reverse_iterator`

typedef reverse_iterator<iterator>reverse_iterator;

The type describes an object that can serve as a reverse bidirectional iterator for the controlled sequence.

`hash_map::size`

size_typesize() const;

The member function returns the length of the controlled sequence.

`hash_map::size_type`

typedef T2size_type;

The unsigned integer type describes an object that can represent the
length of any controlled sequence. It is described here as a
synonym for the implementation-defined type `T2`

.

`hash_map::swap`

voidswap(hash_map& right);

The member function swaps the controlled sequences between
`*this`

and `right`

. If
```
get_allocator()
== right.get_allocator()
```

, it does so in constant time,
it throws an exception only as a result of copying the stored
traits object of type `Tr`

, and it invalidates no references, pointers,
or iterators that designate elements in the two controlled sequences.
Otherwise, it performs a number of element assignments and constructor calls
proportional to the number of elements in the two controlled sequences.

`hash_map::upper_bound`

iteratorupper_bound(const Key& keyval); const_iteratorupper_bound(const Key& keyval) const;

The member function returns an iterator
just beyond the iterator that designates the
latest element `X`

in the controlled sequence
for which `X.first`

has
equivalent ordering
to `keyval`

.
If no such element exists, the function returns
`end()`

.

`hash_map::value_comp`

value_comparevalue_comp() const;

The member function returns a function object that determines the order of elements in the controlled sequence.

`hash_map::value_compare`

classvalue_compare: public binary_function<value_type, value_type, bool> { public: bool operator()(const value_type& left, const value_type& right) const {return (comp(left.first, right.first)); } protected: value_compare(key_compare pr) : comp(pr) {} key_compare comp; };

The type describes a function object that can compare the
sort keys in two elements to determine their relative order
in the controlled sequence. The function object stores an object
** comp**
of type

`key_type`

.
The member function **uses this object to compare the sort-key components of two element.**

`operator()`

`hash_map::value_type`

typedef pair<const Key, Ty>value_type;

The type describes an element of the controlled sequence.

`hash_multimap`

```
allocator_type
· begin
· bucket
· bucket_count
· bucket_size
· clear
· const_iterator
· const_local_iterator
· const_pointer
· const_reference
· const_reverse_iterator
· count
· difference_type
· empty
· end
· equal_range
· erase
· find
· get_allocator
· insert
· iterator
· key_comp
· key_compare
· key_type
· load_factor
· local_iterator
· lower_bound
· mapped_type
· max_bucket_count
· max_load_factor
· max_size
· hash_multimap
· rbegin
· reference
· rehash
· rend
· reverse_iterator
· size
· size_type
· swap
· upper_bound
· value_comp
· value_compare
· value_type
```

template<class Key, class Ty, class Tr = hash_compare<Key, less<Key> >, class Alloc = allocator<pair<const Key, Ty> > > classhash_multimap{ public: typedef Keykey_type; typedef Tymapped_type; typedef Trkey_compare; typedef Allocallocator_type; typedef pair<const Key, Ty>value_type; classvalue_compare; typedef Alloc::pointerpointer; typedef Alloc::const_pointerconst_pointer; typedef Alloc::referencereference; typedef Alloc::const_referenceconst_reference; typedef T0iterator; typedef T1const_iterator; typedef T2size_type; typedef T3difference_type; typedef T4local_iterator; typedef T5const_local_iterator; typedef reverse_iterator<const_iterator>const_reverse_iterator; typedef reverse_iterator<iterator>reverse_iterator;hash_multimap(); explicithash_multimap(const Tr& traits);hash_multimap(const Tr& traits, const Alloc& al);hash_multimap(const hash_multimap& right); template<class InIt>hash_multimap(InIt first, InIt last); template<class InIt>hash_multimap(InIt first, InIt last, const Tr& traits); template<class InIt>hash_multimap(InIt first, InIt last, const Tr& traits, const Alloc& al); iteratorbegin(); const_iteratorbegin() const; local_iteratorbegin(size_type nbucket); const_local_iteratorbegin(size_type nbucket) const; iteratorend(); const_iteratorend() const; local_iteratorend(size_type nbucket); const_local_iteratorend(size_type nbucket) const; reverse_iteratorrbegin(); const_reverse_iteratorrbegin() const; reverse_iteratorrend(); const_reverse_iteratorrend() const; size_typesize() const; size_typemax_size() const; boolempty() const; size_typebucket_count() const; size_typemax_bucket_count() const; size_typebucket(const Key& keyval) const; size_typebucket_size(size_type nbucket) const; key_comparekey_comp() const; value_comparevalue_comp() const; Allocget_allocator() const; floatload_factor() const; floatmax_load_factor() const; voidmax_load_factor(float factor); voidrehash(size_type nbuckets); iteratorinsert(const value_type& val); iteratorinsert(iterator where, const value_type& val); template<class InIt> voidinsert(InIt first, InIt last); iteratorerase(iterator where); iteratorerase(iterator first, iterator last); size_typeerase(const Key& keyval); voidclear(); voidswap(hash_multimap& right); iteratorfind(const Key& keyval); const_iteratorfind(const Key& keyval) const; size_typecount(const Key& keyval) const; iteratorlower_bound(const Key& keyval); const_iteratorlower_bound(const Key& keyval) const; iteratorupper_bound(const Key& keyval); const_iteratorupper_bound(const Key& keyval) const; pair<iterator, iterator>equal_range(const Key& keyval); pair<const_iterator, const_iterator>equal_range(const Key& keyval) const; };

The template class describes an object that controls a
varying-length sequence of elements of type
`pair<const Key, Ty>`

.
The sequence is
ordered by the
hash traits object
`Tr`

, which includes two functions:

- a one-operand
**hash function**, which partitions the sequence into an ordered set of subsequences called**buckets**. -
a two-operand
**comparison function**for imposing a strict weak ordering within each bucket.

Each element stores two objects, a **sort key** and a **value**.
The sequence is represented in a way that permits lookup, insertion,
and removal of an arbitrary element with a number of operations that can be
independent of the number of elements in the sequence (constant time),
at least when all buckets are of roughly equal length.
In the worst case, when all of the elements are in one bucket,
the number of operations is proportional to the number of elements
in the sequence (linear time). Moreover, inserting an element
invalidates no iterators, and removing an element
invalidates only those iterators which point at the removed element.

The object orders the sequence it controls by calling a stored
hash traits object of type `Tr`

.
You access this stored object by calling the member function
`key_comp()`

.
Such a traits object must behave the same as an object of class
`hash_compare<Key, Pr>`

.
Specifically, for all values `keyval`

of type `Key`

,
the call `key_comp()(keyval)`

yields a distribution
of values of type `size_t`

.
Moreover, class `Tr`

imposes a
strict weak ordering
on sort keys of type `Key`

.
For any element `X`

that precedes
`Y`

in the sequence and has the same hash value,
```
key_comp()(Y.first,
X.first)
```

is false. (For the default function object
`less<Key>`

,
sort keys never decrease in value.)
Unlike template class `hash_map`

,
an object of template class `hash_multimap`

does not ensure that
`key_comp()(X.first, Y.first)`

is true.
(Keys need not be unique.)

The object also stores a **maximum load factor**, which specifies the
maximum desired average number of elements per bucket. If inserting an element
causes `load_factor()`

to exceed the maximum load factor, the container increases the number of
buckets and rebuilds the hash table as needed.

The actual order of elements in the controlled sequence depends on the hash function, the comparison function, the order of insertion, the maximum load factor, and the current number of buckets. You cannot in general predict the order of elements in the controlled sequence. You can always be assured, however, that any subset of elements that have equivalent ordering are adjacent in the controlled sequence.

The object allocates and frees storage for the sequence it controls
through a stored allocator object
of class `Alloc`

. Such an allocator object must have
the same external interface as an object of template class
`allocator`

.
Note that the stored allocator object is *not* copied when the container
object is assigned.

`hash_multimap::allocator_type`

typedef Allocallocator_type;

The type is a synonym for the template parameter `Alloc`

.

`hash_multimap::begin`

iteratorbegin(); const_iteratorbegin() const; local_iteratorbegin(size_type nbucket); const_local_iteratorbegin(size_type nbucket) const;

The first two member functions return a forward iterator that points at
the first element of the sequence (or just beyond the end of an empty
sequence). The last two member functions return a forward iterator that points at
the first element of bucket `nbucket`

(or just beyond the end of an empty
bucket).

`hash_multimap::bucket`

size_typebucket(const Key& keyval) const;

The member function returns the bucket number currently corresponding
to the key value `keyval`

.

`hash_multimap::bucket_count`

size_typebucket_count() const;

The member function returns the current number of buckets.

`hash_multimap::bucket_size`

size_typebucket_size(size_type nbucket) const;

The member functions returns the size of bucket number `nbucket`

.

`hash_multimap::clear`

voidclear();

The member function calls
```
erase(
begin(),
end())
```

.

`hash_multimap::const_iterator`

typedef T1const_iterator;

The type describes an object that can serve as a constant
bidirectional iterator for the controlled sequence.
It is described here as a
synonym for the implementation-defined type `T1`

.

`hash_multimap::const_local_iterator`

typedef T5const_local_iterator;

The type describes an object that can serve as a constant
forward iterator for a bucket.
It is described here as a
synonym for the implementation-defined type `T5`

.

`hash_multimap::const_pointer`

typedef Alloc::const_pointerconst_pointer;

The type describes an object that can serve as a constant pointer to an element of the controlled sequence.

`hash_multimap::const_reference`

typedef Alloc::const_referenceconst_reference;

The type describes an object that can serve as a constant reference to an element of the controlled sequence.

`hash_multimap::const_reverse_iterator`

typedef reverse_iterator<const_iterator>const_reverse_iterator;

The type describes an object that can serve as a constant reverse bidirectional iterator for the controlled sequence.

`hash_multimap::count`

size_typecount(const Key& keyval) const;

The member function returns the number of elements in the range
```
[lower_bound(keyval),
upper_bound(keyval)).
```

`hash_multimap::difference_type`

typedef T3difference_type;

The signed integer type describes an object that can represent the
difference between the addresses of any two elements in the controlled
sequence. It is described here as a
synonym for the implementation-defined type `T3`

.

`hash_multimap::empty`

boolempty() const;

The member function returns true for an empty controlled sequence.

`hash_multimap::end`

iteratorend(); const_iteratorend() const; local_iteratorend(size_type nbucket); const_local_iteratorend(size_type nbucket) const;

The first two member functions return a forward iterator that points
just beyond the end of the sequence.
The last two member functions return a forward iterator that points
just beyond the end of bucket `nbucket`

.

`hash_multimap::equal_range`

pair<iterator, iterator>equal_range(const Key& keyval); pair<const_iterator, const_iterator>equal_range(const Key& keyval) const;

The member function returns a pair of iterators `X`

such that ```
X.first ==
lower_bound(keyval)
```

and ```
X.second ==
upper_bound(keyval)
```

.

`hash_multimap::erase`

iteratorerase(iterator where); iteratorerase(iterator first, iterator last); size_typeerase(const Key& keyval);

The first member function removes the element of the controlled
sequence pointed to by `where`

.
The second member function removes the elements
in the range `[first, last)`

.
Both return an iterator that designates the first element remaining
beyond any elements removed, or
`end()`

if no such element exists.

The third member removes
the elements with sort keys in the range
```
[lower_bound(keyval),
upper_bound(keyval)).
```

It returns the number of elements it removes.

The member functions never throw an exception.

`hash_multimap::find`

iteratorfind(const Key& keyval); const_iteratorfind(const Key& keyval) const;

The member function returns
`lower_bound(keyval)`

.

`hash_multimap::get_allocator`

Allocget_allocator() const;

The member function returns the stored allocator object.

`hash_multimap::hash_multimap`

hash_multimap(); explicithash_multimap(const Tr& traits);hash_multimap(const Tr& traits, const Alloc& al);hash_multimap(const hash_multimap& right); template<class InIt>hash_multimap(InIt first, InIt last); template<class InIt>hash_multimap(InIt first, InIt last, const Tr& traits); template<class InIt>hash_multimap(InIt first, InIt last, const Tr& traits, const Alloc& al);

All constructors store an
allocator object and
initialize the controlled sequence. The allocator object is the argument
`al`

, if present. For the copy constructor, it is
`right.get_allocator()`

.
Otherwise, it is `Alloc()`

.

All constructors also store a
hash traits object that can later
be returned by calling
`key_comp()`

.
The hash traits object is the argument `traits`

, if present.
For the copy constructor, it is
`right.key_comp()`

).
Otherwise, it is `Tr()`

.

The first three constructors specify an
empty initial controlled sequence. The fourth constructor specifies
a copy of the sequence controlled by `right`

.
The last three constructors specify the sequence of element values
`[first, last)`

.

`hash_multimap::insert`

iteratorinsert(const value_type& val); iteratorinsert(iterator where, const value_type& val); template<class InIt> voidinsert(InIt first, InIt last);

The first member function inserts the element `val`

in the controlled sequence, then returns
the iterator that designates the inserted element.
The second member function returns `insert(val)`

,
using `where`

as a starting place within the controlled
sequence to search for the insertion point. (Insertion can
possibly occur somewhat faster, if the
insertion point immediately precedes or follows `where`

.)
The third member function
inserts the sequence of element values,
for each `where`

in the range `[first, last)`

,
by calling `insert(*where)`

.

If an exception is thrown during the insertion of a single element, the container is left unaltered and the exception is rethrown. If an exception is thrown during the insertion of multiple elements, the container is left in a stable but unspecified state and the exception is rethrown.

`hash_multimap::iterator`

typedef T0iterator;

The type describes an object that can serve as a bidirectional
iterator for the controlled sequence.
It is described here as a
synonym for the implementation-defined type `T0`

.

`hash_multimap::key_comp`

key_comparekey_comp() const;

The member function returns the stored hash traits object that determines the order of elements in the controlled sequence. In particular, the stored object defines the member function:

bool operator()(const Key& left, const Key& right);

which returns true if `left`

strictly
precedes `right`

in the sort order.

`hash_multimap::key_compare`

typedef Trkey_compare;

The type describes a traits object that behaves much like an object of class
`hash_compare<Key, Pr>`

.
In particular, it can compare two
sort keys to determine the relative order of two
elements in the controlled sequence.

`hash_multimap::key_type`

typedef Keykey_type;

The type describes the sort key object stored in each element of the controlled sequence.

`hash_multimap::load_factor`

floatload_factor() const;

The member function returns
```
(float)size() /
(float)bucket_count()
```

,
the average number of elements per bucket.

`hash_multimap::local_iterator`

typedef T4local_iterator;

The type describes an object that can serve as a
forward iterator for a bucket.
It is described here as a
synonym for the implementation-defined type `T4`

.

`hash_multimap::lower_bound`

iteratorlower_bound(const Key& keyval); const_iteratorlower_bound(const Key& keyval) const;

The member function returns an iterator that designates the
earliest element `X`

in the controlled sequence for which
```
key_comp()(X.
first, keyval)
```

is
false.

`end()`

.
`hash_multimap::mapped_type`

typedef Tymapped_type;

The type is a synonym for the template parameter `Ty`

.

`hash_multimap::max_bucket_count`

size_typemax_bucket_count() const;

The member function returns the maximum number of buckets currently permitted.

`hash_multimap::max_load_factort`

floatmax_load_factor() const; voidmax_load_factor(float factor);

The first member function returns the stored maximum load factor.
The second member function replaces the stored maximum load factor with `factor`

.

`hash_multimap::max_size`

size_typemax_size() const;

The member function returns the length of the longest sequence that the object can control.

`hash_multimap::pointer`

typedef Alloc::pointerpointer;

The type describes an object that can serve as a pointer to an element of the controlled sequence.

`hash_multimap::rbegin`

const_reverse_iteratorrbegin() const; reverse_iteratorrbegin();

The member function returns a reverse bidirectional iterator that points just beyond the end of the controlled sequence. Hence, it designates the beginning of the reverse sequence.

`hash_multimap::reference`

typedef Alloc::referencereference;

The type describes an object that can serve as a reference to an element of the controlled sequence.

`hash_multimap::rehash`

voidrehash(size_type nbuckets);

The member function alters the number of buckets to be at least `nbuckets`

and rebuilds the hash table as needed.

`hash_multimap::rend`

const_reverse_iteratorrend() const; reverse_iteratorrend();

The member function returns a reverse bidirectional iterator that points at the first element of the sequence (or just beyond the end of an empty sequence). Hence, it designates the end of the reverse sequence.

`hash_multimap::reverse_iterator`

typedef reverse_iterator<iterator>reverse_iterator;

The type describes an object that can serve as a reverse bidirectional iterator for the controlled sequence.

`hash_multimap::size`

size_typesize() const;

The member function returns the length of the controlled sequence.

`hash_multimap::size_type`

typedef T2size_type;

The unsigned integer type describes an object that can represent the
length of any controlled sequence. It is described here as a
synonym for the implementation-defined type `T2`

.

`hash_multimap::swap`

voidswap(hash_multimap& right);

The member function swaps the controlled sequences between
`*this`

and `right`

. If
```
get_allocator()
== right.get_allocator()
```

, it does so in constant time,
it throws an exception only as a result of copying the stored
traits object of type `Tr`

, and it invalidates no references, pointers,
or iterators that designate elements in the two controlled sequences.
Otherwise, it performs a number of element assignments and constructor calls
proportional to the number of elements in the two controlled sequences.

`hash_multimap::upper_bound`

iteratorupper_bound(const Key& keyval); const_iteratorupper_bound(const Key& keyval) const;

The member function returns an iterator
just beyond the iterator that designates the
latest element `X`

in the controlled sequence
for which `X.first`

has
equivalent ordering
to `keyval`

.
If no such element exists, the function returns
`end()`

.

`hash_multimap::value_comp`

value_comparevalue_comp() const;

The member function returns a function object that determines the order of elements in the controlled sequence.

`hash_multimap::value_compare`

classvalue_compare: public binary_function<value_type, value_type, bool> { public: bool operator()(const value_type& left, const value_type& right) const {return (comp(left.first, right.first)); } protected: value_compare(key_compare pr) : comp(pr) {} key_compare comp; };

The type describes a function object that can compare the
sort keys in two elements to determine their relative order
in the controlled sequence. The function object stores an object
** comp**
of type

`key_type`

.
The member function **uses this object to compare the sort-key components of two element.**

`operator()`

`hash_multimap::value_type`

typedef pair<const Key, Ty>value_type;

The type describes an element of the controlled sequence.

`operator!=`

template<class Key, class Ty, class Tr, class Alloc> booloperator!=( const hash_map <Key, Ty, Tr, Alloc>& left, const hash_map <Key, Ty, Tr, Alloc>& right); template<class Key, class Ty, class Tr, class Alloc> booloperator!=( const hash_multimap <Key, Ty, Tr, Alloc>& left, const hash_multimap <Key, Ty, Tr, Alloc>& right);

The template function returns `!(left == right)`

.

`operator==`

template<class Key, class Ty, class Tr, class Alloc> booloperator==( const hash_map <Key, Ty, Tr, Alloc>& left, const hash_map <Key, Ty, Tr, Alloc>& right); template<class Key, class Ty, class Tr, class Alloc> booloperator==( const hash_multimap <Key, Ty, Tr, Alloc>& left, const hash_multimap <Key, Ty, Tr, Alloc>& right);

The first template function overloads `operator==`

to compare two objects of template class
`hash_map`

.
The second template function overloads `operator==`

to compare two objects of template class
`hash_multimap`

.
Both functions return
```
left.size() == right.size() &&
equal(left.
begin(), left.
end(), right.begin())
```

.

`operator<`

template<class Key, class Ty, class Tr, class Alloc> booloperator<( const hash_map <Key, Ty, Tr, Alloc>& left, const hash_map <Key, Ty, Tr, Alloc>& right); template<class Key, class Ty, class Tr, class Alloc> booloperator<( const hash_multimap <Key, Ty, Tr, Alloc>& left, const hash_multimap <Key, Ty, Tr, Alloc>& right);

The first template function overloads `operator<`

to compare two objects of template class
`hash_map`

.
The second template function overloads `operator<`

to compare two objects of template class
`hash_multimap`

.
Both functions return
```
lexicographical_compare(left.
begin(), left.
end(), right.begin(), right.end(),
left.value_comp())
```

.

`operator<=`

template<class Key, class Ty, class Tr, class Alloc> booloperator<=( const hash_map <Key, Ty, Tr, Alloc>& left, const hash_map <Key, Ty, Tr, Alloc>& right); template<class Key, class Ty, class Tr, class Alloc> booloperator<=( const hash_multimap <Key, Ty, Tr, Alloc>& left, const hash_multimap <Key, Ty, Tr, Alloc>& right);

The template function returns `!(right < left)`

.

`operator>`

template<class Key, class Ty, class Tr, class Alloc> booloperator>( const hash_map <Key, Ty, Tr, Alloc>& left, const hash_map <Key, Ty, Tr, Alloc>& right); template<class Key, class Ty, class Tr, class Alloc> booloperator>( const hash_multimap <Key, Ty, Tr, Alloc>& left, const hash_multimap <Key, Ty, Tr, Alloc>& right);

The template function returns `right < left`

.

`operator>=`

template<class Key, class Ty, class Tr, class Alloc> booloperator>=( const hash_map <Key, Ty, Tr, Alloc>& left, const hash_map <Key, Ty, Tr, Alloc>& right); template<class Key, class Ty, class Tr, class Alloc> booloperator!=( const hash_multimap <Key, Ty, Tr, Alloc>& left, const hash_multimap <Key, Ty, Tr, Alloc>& right);

The template function returns `!(left < right)`

.

`swap`

template<class Key, class Ty, class Tr, class Alloc> voidswap( hash_map <Key, Ty, Tr, Alloc>& left, hash_map <Key, Ty, Tr, Alloc>& right); template<class Key, class Ty, class Tr, class Alloc> voidswap( hash_multimap <Key, Ty, Tr, Alloc>& left, hash_multimap <Key, Ty, Tr, Alloc>& right);

The template function executes
`left.swap(right)`

.

See also the
**Table of Contents** and the
**Index**.

*
Copyright © 1992-2006
by P.J. Plauger. All rights reserved.*

Last modified: 2013-12-21