<hash_map>

<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>
    class hash_compare;
template<class Key, class Ty, class Tr, class Alloc>
    class hash_map;
template<class Key, class Ty, class Tr, class Alloc>
    class hash_multimap;

        // TEMPLATE FUNCTIONS
template<class Key, class Ty, class Tr, class Alloc>
    bool operator==(
        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>
    bool operator==(
        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>
    bool operator!=(
        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>
    bool operator!=(
        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>
    bool operator<(
        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>
    bool operator<(
        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>
    bool operator>(
        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>
    bool operator>(
        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>
    bool operator<=(
        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>
    bool operator<=(
        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>
    bool operator>=(
        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>
    bool operator>=(
        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>
    void swap(
        hash_map<Key, Ty, Tr, Alloc>& left,
        hash_map<Key, Ty, Tr, Alloc>& right);
template<class Key, class Ty, class Tr, class Alloc>
    void swap(
        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> >
    class hash_compare {
    Pr comp;
public:
    const size_t bucket_size = 4;
    const size_t min_buckets = 8;
    hash_compare();
    hash_compare(Pr pred);
    size_t operator()(const Key& Key) const;
    bool operator()(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> > >
    class hash_map {
public:
    typedef Key key_type;
    typedef Ty mapped_type;
    typedef Tr key_compare;
    typedef Alloc allocator_type;

    typedef pair<const Key, Ty> value_type;
    class value_compare;
    typedef Alloc::pointer pointer;
    typedef Alloc::const_pointer const_pointer;
    typedef Alloc::reference reference;
    typedef Alloc::const_reference const_reference;

    typedef T0 iterator;
    typedef T1 const_iterator;
    typedef T2 size_type;
    typedef T3 difference_type;
    typedef T4 local_iterator;
    typedef T5 const_local_iterator;
    typedef reverse_iterator<const_iterator>
        const_reverse_iterator;
    typedef reverse_iterator<iterator> reverse_iterator;

    hash_map();
    explicit hash_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);

    iterator begin();
    const_iterator begin() const;
    local_iterator begin(size_type nbucket);
    const_local_iterator begin(size_type nbucket) const;

    iterator end();
    const_iterator end() const;
    local_iterator end(size_type nbucket);
    const_local_iterator end(size_type nbucket) const;

    reverse_iterator rbegin();
    const_reverse_iterator rbegin() const;
    reverse_iterator rend();
    const_reverse_iterator rend() const;

    size_type size() const;
    size_type max_size() const;
    bool empty() const;

    size_type bucket_count() const;
    size_type max_bucket_count() const;
    size_type bucket(const Key& keyval) const;
    size_type bucket_size(size_type nbucket) const;

    key_compare key_comp() const;
    value_compare value_comp() const;
    Alloc get_allocator() const;

    float load_factor() const;
    float max_load_factor() const;
    void max_load_factor(float factor);
    void rehash(size_type nbuckets);

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

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

    iterator erase(iterator where);
    iterator erase(iterator first, iterator last);
    size_type erase(const Key& keyval);
    void clear();

    void swap(hash_map& right);

    iterator find(const Key& keyval);
    const_iterator find(const Key& keyval) const;
    size_type count(const Key& keyval) const;
    iterator lower_bound(const Key& keyval);
    const_iterator lower_bound(const Key& keyval) const;
    iterator upper_bound(const Key& keyval);
    const_iterator upper_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 Alloc allocator_type;

The type is a synonym for the template parameter Alloc.

hash_map::begin

iterator begin();
    const_iterator begin() const;
    local_iterator begin(size_type nbucket);
    const_local_iterator begin(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_type bucket(const Key& keyval) const;

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

hash_map::bucket_count

size_type bucket_count() const;

The member function returns the current number of buckets.

hash_map::bucket_size

size_type bucket_size(size_type nbucket) const;

The member functions returns the size of bucket number nbucket.

hash_map::clear

void clear();

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

hash_map::const_iterator

typedef T1 const_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 T5 const_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_pointer const_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_reference const_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_type count(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 T3 difference_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

bool empty() const;

The member function returns true for an empty controlled sequence.

hash_map::end

iterator end();
    const_iterator end() const;
    local_iterator end(size_type nbucket);
    const_local_iterator end(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

iterator erase(iterator where);
iterator erase(iterator first, iterator last);
size_type erase(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

iterator find(const Key& keyval);
const_iterator find(const Key& keyval) const;

The member function returns lower_bound(keyval).

hash_map::get_allocator

Alloc get_allocator() const;

The member function returns the stored allocator object.

hash_map::hash_map

hash_map();
explicit hash_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

iterator insert(const value_type& val);
iterator insert(iterator where, const value_type& val);
template<class InIt>
    void insert(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 T0 iterator;

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_compare key_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 Tr key_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 Key key_type;

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

hash_map::load_factor

float load_factor() const;

The member function returns (float)size() / (float)bucket_count(), the average number of elements per bucket.

hash_map::local_iterator

typedef T4 local_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

iterator lower_bound(const Key& keyval);
const_iterator lower_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.

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

hash_map::mapped_type

typedef Ty mapped_type;

The type is a synonym for the template parameter Ty.

hash_map::max_bucket_count

size_type max_bucket_count() const;

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

hash_map::max_load_factort

float max_load_factor() const;
void max_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_type max_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::pointer pointer;

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

hash_map::rbegin

const_reverse_iterator rbegin() const;
reverse_iterator rbegin();

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::reference reference;

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

hash_map::rehash

void rehash(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_iterator rend() const;
reverse_iterator rend();

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_type size() const;

The member function returns the length of the controlled sequence.

hash_map::size_type

typedef T2 size_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

void swap(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

iterator upper_bound(const Key& keyval);
const_iterator upper_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_compare value_comp() const;

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

hash_map::value_compare

class value_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 operator() uses this object to compare the sort-key components of two element.

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> > >
    class hash_multimap {
public:
    typedef Key key_type;
    typedef Ty mapped_type;
    typedef Tr key_compare;
    typedef Alloc allocator_type;

    typedef pair<const Key, Ty> value_type;
    class value_compare;
    typedef Alloc::pointer pointer;
    typedef Alloc::const_pointer const_pointer;
    typedef Alloc::reference reference;
    typedef Alloc::const_reference const_reference;

    typedef T0 iterator;
    typedef T1 const_iterator;
    typedef T2 size_type;
    typedef T3 difference_type;
    typedef T4 local_iterator;
    typedef T5 const_local_iterator;
    typedef reverse_iterator<const_iterator>
        const_reverse_iterator;
    typedef reverse_iterator<iterator> reverse_iterator;

    hash_multimap();
    explicit hash_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);

    iterator begin();
    const_iterator begin() const;
    local_iterator begin(size_type nbucket);
    const_local_iterator begin(size_type nbucket) const;

    iterator end();
    const_iterator end() const;
    local_iterator end(size_type nbucket);
    const_local_iterator end(size_type nbucket) const;

    reverse_iterator rbegin();
    const_reverse_iterator rbegin() const;
    reverse_iterator rend();
    const_reverse_iterator rend() const;

    size_type size() const;
    size_type max_size() const;
    bool empty() const;

    size_type bucket_count() const;
    size_type max_bucket_count() const;
    size_type bucket(const Key& keyval) const;
    size_type bucket_size(size_type nbucket) const;

    key_compare key_comp() const;
    value_compare value_comp() const;
    Alloc get_allocator() const;

    float load_factor() const;
    float max_load_factor() const;
    void max_load_factor(float factor);
    void rehash(size_type nbuckets);

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

    iterator erase(iterator where);
    iterator erase(iterator first, iterator last);
    size_type erase(const Key& keyval);
    void clear();

    void swap(hash_multimap& right);

    iterator find(const Key& keyval);
    const_iterator find(const Key& keyval) const;
    size_type count(const Key& keyval) const;
    iterator lower_bound(const Key& keyval);
    const_iterator lower_bound(const Key& keyval) const;
    iterator upper_bound(const Key& keyval);
    const_iterator upper_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 Alloc allocator_type;

The type is a synonym for the template parameter Alloc.

hash_multimap::begin

iterator begin();
    const_iterator begin() const;
    local_iterator begin(size_type nbucket);
    const_local_iterator begin(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_type bucket(const Key& keyval) const;

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

hash_multimap::bucket_count

size_type bucket_count() const;

The member function returns the current number of buckets.

hash_multimap::bucket_size

size_type bucket_size(size_type nbucket) const;

The member functions returns the size of bucket number nbucket.

hash_multimap::clear

void clear();

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

hash_multimap::const_iterator

typedef T1 const_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 T5 const_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_pointer const_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_reference const_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_type count(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 T3 difference_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

bool empty() const;

The member function returns true for an empty controlled sequence.

hash_multimap::end

iterator end();
    const_iterator end() const;
    local_iterator end(size_type nbucket);
    const_local_iterator end(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

iterator erase(iterator where);
iterator erase(iterator first, iterator last);
size_type erase(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

iterator find(const Key& keyval);
const_iterator find(const Key& keyval) const;

The member function returns lower_bound(keyval).

hash_multimap::get_allocator

Alloc get_allocator() const;

The member function returns the stored allocator object.

hash_multimap::hash_multimap

hash_multimap();
explicit hash_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

iterator insert(const value_type& val);
iterator insert(iterator where, const value_type& val);
template<class InIt>
    void insert(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 T0 iterator;

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_compare key_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 Tr key_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 Key key_type;

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

hash_multimap::load_factor

float load_factor() const;

The member function returns (float)size() / (float)bucket_count(), the average number of elements per bucket.

hash_multimap::local_iterator

typedef T4 local_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

iterator lower_bound(const Key& keyval);
const_iterator lower_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.

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

hash_multimap::mapped_type

typedef Ty mapped_type;

The type is a synonym for the template parameter Ty.

hash_multimap::max_bucket_count

size_type max_bucket_count() const;

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

hash_multimap::max_load_factort

float max_load_factor() const;
void max_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_type max_size() const;

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

hash_multimap::pointer

typedef Alloc::pointer pointer;

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

hash_multimap::rbegin

const_reverse_iterator rbegin() const;
reverse_iterator rbegin();

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::reference reference;

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

hash_multimap::rehash

void rehash(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_iterator rend() const;
reverse_iterator rend();

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_type size() const;

The member function returns the length of the controlled sequence.

hash_multimap::size_type

typedef T2 size_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

void swap(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

iterator upper_bound(const Key& keyval);
const_iterator upper_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_compare value_comp() const;

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

hash_multimap::value_compare

class value_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 operator() uses this object to compare the sort-key components of two element.

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>
    bool operator!=(
        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>
    bool operator!=(
        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>
    bool operator==(
        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>
    bool operator==(
        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>
    bool operator<(
        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>
    bool operator<(
        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>
    bool operator<=(
        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>
    bool operator<=(
        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>
    bool operator>(
        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>
    bool operator>(
        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>
    bool operator>=(
        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>
    bool operator!=(
        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>
    void swap(
        hash_map <Key, Ty, Tr, Alloc>& left,
        hash_map <Key, Ty, Tr, Alloc>& right);
template<class Key, class Ty, class Tr, class Alloc>
    void swap(
        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



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