hash_multimap

Category: containers		Component type: type

Description

Hash_multimap is a HashedAssociativeContainer that associates objects of type Key with objects of type Data. Hash_multimap is a PairAssociativeContainer, meaning that its value type is pair<const Key, Data>. It is also a MultipleAssociativeContainer, meaning that there is no limit on the number of elements whose keys may compare equal using EqualKey.

Looking up an element in a hash_multimap by its key is efficient, so hash_multimap is useful for "dictionaries" where the order of elements is irrelevant. If it is important for the elements to be in a particular order, however, then Multimap is more appropriate.

Example

struct eqstr
{
  bool operator()(const char* s1, const char* s2) const
  {
    return strcmp(s1, s2) == 0;
  }
};

typedef hash_multimap<const char*, int, hash<const char*>, eqstr> map_type;

void lookup(const map_type& Map, const char* str)
{
  cout << str << ": ";
  pair<map_type::const_iterator, map_type::const_iterator> p =
    Map.equal_range(str);
  for (map_type::const_iterator i = p.first; i != p.second; ++i)
    cout << (*i).second << " ";
  cout << endl;
}

int main()
{
  map_type M;
  M.insert(map_type::value_type("H", 1));
  M.insert(map_type::value_type("H", 2));
  M.insert(map_type::value_type("C", 12));
  M.insert(map_type::value_type("C", 13));
  M.insert(map_type::value_type("O", 16));
  M.insert(map_type::value_type("O", 17));
  M.insert(map_type::value_type("O", 18));
  M.insert(map_type::value_type("I", 127));

  lookup(M, "I");
  lookup(M, "O");
  lookup(M, "Rn");
}

Definition

Defined in the header hash_map, and in the backward-compatibility header hash_map.h. This class is an SGI extension; it is not part of the C++ standard.

Template parameters

Parameter	Description	Default
Key	The hash_multimap's key type. This is also defined as hash_multimap::key_type.
Data	The hash_multimap's data type. This is also defined as hash_multimap::data_type.
HashFcn	The HashFunction used by the hash_multimap. This is also defined as hash_multimap::hasher.	hash<Key>
EqualKey	The hash_multimap's key equality function: a BinaryPredicate that determines whether two keys are equal. This is also defined as hash_multimap::key_equal.	equal_to<Key>
Alloc	The hash_set's allocator, used for all internal memory management.	Allocators

Model of

MultipleHashedAssociativeContainer, PairAssociativeContainer

Type requirements

• Key is Assignable.
• EqualKey is a BinaryPredicate whose argument type is Key.
• EqualKey is an equivalence relation.
• Alloc is an Allocators.

Public base classes

None.

Members

Member	Where defined	Description
key_type	AssociativeContainer	The hash_multimap's key type, Key.
data_type	PairAssociativeContainer	The type of object associated with the keys.
value_type	PairAssociativeContainer	The type of object, pair<const key_type, data_type>, stored in the hash_multimap.
hasher	HashedAssociativeContainer	The hash_multimap's HashFunction.
key_equal	HashedAssociativeContainer	functors that compares keys for equality.
pointer	Container	Pointer to T.
reference	Container	Reference to T
const_reference	Container	Const reference to T
size_type	Container	An unsigned integral type.
difference_type	Container	A signed integral type.
iterator	Container	Iterator used to iterate through a hash_multimap. [1]
const_iterator	Container	Const iterator used to iterate through a hash_multimap.
iterator begin()	Container	Returns an iterator pointing to the beginning of the hash_multimap.
iterator end()	Container	Returns an iterator pointing to the end of the hash_multimap.
const_iterator begin() const	Container	Returns an const_iterator pointing to the beginning of the hash_multimap.
const_iterator end() const	Container	Returns an const_iterator pointing to the end of the hash_multimap.
size_type size() const	Container	Returns the size of the hash_multimap.
size_type max_size() const	Container	Returns the largest possible size of the hash_multimap.
bool empty() const	Container	true if the hash_multimap's size is 0.
size_type bucket_count() const	HashedAssociativeContainer	Returns the number of buckets used by the hash_multimap.
void resize(size_type n)	HashedAssociativeContainer	Increases the bucket count to at least n.
hasher hash_funct() const	HashedAssociativeContainer	Returns the hasher object used by the hash_multimap.
key_equal key_eq() const	HashedAssociativeContainer	Returns the key_equal object used by the hash_multimap.
hash_multimap()	Container	Creates an empty hash_multimap.
hash_multimap(size_type n)	HashedAssociativeContainer	Creates an empty hash_multimap with at least n buckets.
hash_multimap(size_type n, const hasher& h)	HashedAssociativeContainer	Creates an empty hash_multimap with at least n buckets, using h as the hash function.
hash_multimap(size_type n, const hasher& h, const key_equal& k)	HashedAssociativeContainer	Creates an empty hash_multimap with at least n buckets, using h as the hash function and k as the key equal function.
template <class InputIterator> hash_multimap(InputIterator, InputIterator) [2]	MultipleHashedAssociativeContainer	Creates a hash_multimap with a copy of a range.
template <class InputIterator> hash_multimap(InputIterator, InputIterator, size_type n) [2]	MultipleHashedAssociativeContainer	Creates a hash_multimap with a copy of a range and a bucket count of at least n.
template <class InputIterator> hash_multimap(InputIterator, InputIterator, size_type n, const hasher& h) [2]	MultipleHashedAssociativeContainer	Creates a hash_multimap with a copy of a range and a bucket count of at least n, using h as the hash function.
template <class InputIterator> hash_multimap(InputIterator, InputIterator, size_type n, const hasher& h, const key_equal& k) [2]	MultipleHashedAssociativeContainer	Creates a hash_multimap with a copy of a range and a bucket count of at least n, using h as the hash function and k as the key equal function.
hash_multimap(const hash_multimap&)	Container	The copy constructor.
hash_multimap& operator=(const hash_multimap&)	Container	The assignment operator
void swap(hash_multimap&)	Container	Swaps the contents of two hash_multimaps.
iterator insert(const value_type& x)	MultipleAssociativeContainer	Inserts x into the hash_multimap.
template <class InputIterator> void insert(InputIterator, InputIterator) [2]	MultipleAssociativeContainer	Inserts a range into the hash_multimap.
void erase(iterator pos)	AssociativeContainer	Erases the element pointed to by pos.
size_type erase(const key_type& k)	AssociativeContainer	Erases the element whose key is k.
void erase(iterator first, iterator last)	AssociativeContainer	Erases all elements in a range.
void clear()	AssociativeContainer	Erases all of the elements.
const_iterator find(const key_type& k) const	AssociativeContainer	Finds an element whose key is k.
iterator find(const key_type& k)	AssociativeContainer	Finds an element whose key is k.
size_type count(const key_type& k) const	AssociativeContainer	Counts the number of elements whose key is k.
pair<const_iterator, const_iterator> equal_range(const key_type& k) const	AssociativeContainer	Finds a range containing all elements whose key is k.
pair<iterator, iterator> equal_range(const key_type& k)	AssociativeContainer	Finds a range containing all elements whose key is k.
bool operator==(const hash_multimap&, const hash_multimap&)	HashedAssociativeContainer	Tests two hash_multimaps for equality. This is a global function, not a member function.

New members

All of hash_multimap's members are defined in the MultipleHashedAssociativeContainer and PairAssociativeContainer requirements. Hash_multimap does not introduce any new members.

Notes

[1] Hash_multimap::iterator is not a mutable iterator, because hash_multimap::value_type is not Assignable. That is, if i is of type hash_multimap::iterator and p is of type hash_multimap::value_type, then *i = p is not a valid expression. However, hash_multimap::iterator isn't a constant iterator either, because it can be used to modify the object that it points to. Using the same notation as above, (*i).second = p is a valid expression.

[2] This member function relies on member template functions, which at present (early 1998) are not supported by all compilers. If your compiler supports member templates, you can call this function with any type of InputIterator. If your compiler does not yet support member templates, though, then the arguments must either be of type const value_type* or of type hash_multimap::const_iterator.

See also

AssociativeContainer, HashedAssociativeContainer, PairAssociativeContainer, MultipleHashedAssociativeContainer, set, Map, multiset, Multimap, hash_set, hash_map, hash_multiset