hash_set

Category: containers		Component type: type

Description

Hash_set is a HashedAssociativeContainer that stores objects of type Key. Hash_set is a SimpleAssociativeContainer, meaning that its value type, as well as its key type, is Key. It is also a UniqueAssociativeContainer, meaning that no two elements compare equal using the BinaryPredicate EqualKey.

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.

Example

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");
}

Definition

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

Template parameters

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 HashFunction used by the hash_set. This is also defined as hash_set::hasher.	hash<Key>
EqualKey	The hash_set's key equality function: a BinaryPredicate 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.	Allocators

Model of

UniqueHashedAssociativeContainer, SimpleAssociativeContainer

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
value_type	Container	The type of object, T, stored in the hash_set.
key_type	AssociativeContainer	The key type associated with value_type.
hasher	HashedAssociativeContainer	The hash_set'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_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	HashedAssociativeContainer	Returns the number of buckets used by the hash_set.
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_set.
key_equal key_eq() const	HashedAssociativeContainer	Returns the key_equal object used by the hash_set.
hash_set()	Container	Creates an empty hash_set.
hash_set(size_type n)	HashedAssociativeContainer	Creates an empty hash_set with at least n buckets.
hash_set(size_type n, const hasher& h)	HashedAssociativeContainer	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)	HashedAssociativeContainer	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]	UniqueHashedAssociativeContainer	Creates a hash_set with a copy of a range.
template <class InputIterator> hash_set(InputIterator f, InputIterator l, size_type n) [1]	UniqueHashedAssociativeContainer	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]	UniqueHashedAssociativeContainer	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]	UniqueHashedAssociativeContainer	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)	UniqueAssociativeContainer	Inserts x into the hash_set.
template <class InputIterator> void insert(InputIterator f, InputIterator l) [1]	UniqueAssociativeContainer	Inserts a range into the hash_set.
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.
iterator find(const key_type& k) const	AssociativeContainer	Finds an element whose key is k.
size_type count(const key_type& k) const	UniqueAssociativeContainer	Counts the number of elements whose key is k.
pair<iterator, iterator> equal_range(const key_type& k) const	AssociativeContainer	Finds a range containing all elements whose key is k.
bool operator==(const hash_set&, const hash_set&)	HashedAssociativeContainer	Tests two hash_sets for equality. This is a global function, not a member function.

New members

All of hash_set's members are defined in the UniqueHashedAssociativeContainer and SimpleAssociativeContainer requirements. Hash_set does not introduce any new members.

Notes

[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 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_set::const_iterator.

See also

AssociativeContainer, HashedAssociativeContainer, SimpleAssociativeContainer, UniqueHashedAssociativeContainer, set, Map, multiset, Multimap, hash_map, hash_multiset, hash_multimap