
Category: containers  Component type: type 
Hash_set is useful in applications where it is important to be able to search for an element quickly. If it is important for the elements to be in a particular order, however, then set is more appropriate.
struct eqstr { bool operator()(const char* s1, const char* s2) const { return strcmp(s1, s2) == 0; } }; void lookup(const hash_set<const char*, hash<const char*>, eqstr>& Set, const char* word) { hash_set<const char*, hash<const char*>, eqstr>::const_iterator it = Set.find(word); cout << word << ": " << (it != Set.end() ? "present" : "not present") << endl; } int main() { hash_set<const char*, hash<const char*>, eqstr> Set; Set.insert("kiwi"); Set.insert("plum"); Set.insert("apple"); Set.insert("mango"); Set.insert("apricot"); Set.insert("banana"); lookup(Set, "mango"); lookup(Set, "apple"); lookup(Set, "durian"); }
Parameter  Description  Default 

Key  The hash_set's key type and value type. This is also defined as hash_set::key_type and hash_set::value_type  
HashFcn  The Hash Function used by the hash_set. This is also defined as hash_set::hasher.  hash<Key> 
EqualKey  The hash_set's key equality function: a binary predicate that determines whether two keys are equal. This is also defined as hash_set::key_equal.  equal_to<Key> 
Alloc  The hash_set's allocator, used for all internal memory management.  alloc 
Member  Where defined  Description 

value_type  Container  The type of object, T, stored in the hash_set. 
key_type  Associative Container  The key type associated with value_type. 
hasher  Hashed Associative Container  The hash_set'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_set. 
const_iterator  Container  Const iterator used to iterate through a hash_set. (Iterator and const_iterator are the same type.) 
iterator begin() const  Container  Returns an iterator pointing to the beginning of the hash_set. 
iterator end() const  Container  Returns an iterator pointing to the end of the hash_set. 
size_type size() const  Container  Returns the size of the hash_set. 
size_type max_size() const  Container  Returns the largest possible size of the hash_set. 
bool empty() const  Container  true if the hash_set's size is 0. 
size_type bucket_count() const  Hashed Associative Container  Returns the number of buckets used by the hash_set. 
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_set. 
key_equal key_eq() const  Hashed Associative Container  Returns the key_equal object used by the hash_set. 
hash_set()  Container  Creates an empty hash_set. 
hash_set(size_type n)  Hashed Associative Container  Creates an empty hash_set with at least n buckets. 
hash_set(size_type n, const hasher& h) 
Hashed Associative Container  Creates an empty hash_set with at least n buckets, using h as the hash function. 
hash_set(size_type n, const hasher& h, const key_equal& k) 
Hashed Associative Container  Creates an empty hash_set with at least n buckets, using h as the hash function and k as the key equal function. 
template <class InputIterator> hash_set(InputIterator f, InputIterator l) [1] 
Unique Hashed Associative Container  Creates a hash_set with a copy of a range. 
template <class InputIterator> hash_set(InputIterator f, InputIterator l, size_type n) [1] 
Unique Hashed Associative Container  Creates a hash_set with a copy of a range and a bucket count of at least n. 
template <class InputIterator> hash_set(InputIterator f, InputIterator l, size_type n, const hasher& h) [1] 
Unique Hashed Associative Container  Creates a hash_set with a copy of a range and a bucket count of at least n, using h as the hash function. 
hash_set(InputIterator f, InputIterator l, size_type n, const hasher& h, const key_equal& k) [1] 
Unique Hashed Associative Container  Creates a hash_set 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_set(const hash_set&)  Container  The copy constructor. 
hash_set& operator=(const hash_set&)  Container  The assignment operator 
void swap(hash_set&)  Container  Swaps the contents of two hash_sets. 
pair<iterator, bool> insert(const value_type& x) 
Unique Associative Container  Inserts x into the hash_set. 
template <class InputIterator> void insert(InputIterator f, InputIterator l) [1] 
Unique Associative Container  Inserts a range into the hash_set. 
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. 
void clear()  Associative Container  Erases all of the elements. 
iterator find(const key_type& k) const  Associative Container  Finds an element whose key is k. 
size_type count(const key_type& k) const  Unique Associative Container  Counts the number of elements whose key is k. 
pair<iterator, iterator> equal_range(const key_type& k) const 
Associative Container  Finds a range containing all elements whose key is k. 
bool operator==(const hash_set&, const hash_set&) 
Hashed Associative Container  Tests two hash_sets for equality. This is a global function, not a member function. 
[1] 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_set::const_iterator.
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