Category: containers | Component type: type |
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.
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"); }
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 hash function used by the hash_multimap. This is also defined as hash_multimap::hasher. | hash<Key> |
EqualKey | The hash_multimap's key equality function: a binary predicate 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. | alloc |
Member | Where defined | Description |
---|---|---|
key_type | Associative Container | The hash_multimap's key type, Key. |
data_type | Pair Associative Container | The type of object associated with the keys. |
value_type | Pair Associative Container | The type of object, pair<const key_type, data_type>, stored in the hash_multimap. |
hasher | Hashed Associative Container | The hash_multimap's hash function. |
key_equal | Hashed Associative Container | Function object 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 | Hashed Associative Container | Returns the number of buckets used by the hash_multimap. |
void resize(size_type n) | Hashed Associative Container | Increases the bucket count to at least n. |
hasher hash_funct() const | Hashed Associative Container | Returns the hasher object used by the hash_multimap. |
key_equal key_eq() const | Hashed Associative Container | Returns the key_equal object used by the hash_multimap. |
hash_multimap() | Container | Creates an empty hash_multimap. |
hash_multimap(size_type n) | Hashed Associative Container | Creates an empty hash_multimap with at least n buckets. |
hash_multimap(size_type n, const hasher& h) |
Hashed Associative Container | 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) |
Hashed Associative Container | 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] |
Multiple Hashed Associative Container | Creates a hash_multimap with a copy of a range. |
template <class InputIterator> hash_multimap(InputIterator, InputIterator, size_type n) [2] |
Multiple Hashed Associative Container | 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] |
Multiple Hashed Associative Container | 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] |
Multiple Hashed Associative Container | 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) | Multiple Associative Container | Inserts x into the hash_multimap. |
template <class InputIterator> void insert(InputIterator, InputIterator) [2] |
Multiple Associative Container | Inserts a range into the hash_multimap. |
void erase(iterator pos) | Associative Container | Erases the element pointed to by pos. |
size_type erase(const key_type& k) | Associative Container | Erases the element whose key is k. |
void erase(iterator first, iterator last) | Associative Container | Erases all elements in a range. |
const_iterator find(const key_type& k) const | Associative Container | Finds an element whose key is k. |
iterator find(const key_type& k) | Associative Container | Finds an element whose key is k. |
size_type count(const key_type& k) const | Associative Container | Counts the number of elements whose key is k. |
pair<const_iterator, const_iterator> equal_range(const key_type& k) const |
Associative Container | Finds a range containing all elements whose key is k. |
pair<iterator, iterator> equal_range(const key_type& k) |
Associative Container | Finds a range containing all elements whose key is k. |
bool operator==(const hash_multimap&, const hash_multimap&) |
Hashed Associative Container | Tests two hash_multimaps for equality. This is a global function, not a member function. |
[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 input iterator. 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.