...one of the most highly
regarded and expertly designed C++ library projects in the
world.
— Herb Sutter and Andrei
Alexandrescu, C++
Coding Standards
boost::unordered_set — An unordered associative container that stores unique values.
// In header: <boost/unordered_set.hpp> template<typename Value, typename Hash = boost::hash<Value>, typename Pred = std::equal_to<Value>, typename Alloc = std::allocator<Value> > class unordered_set { public: // types typedef Value key_type; typedef Value value_type; typedef Hash hasher; typedef Pred key_equal; typedef Alloc allocator_type; typedef typename allocator_type::pointer pointer; typedef typename allocator_type::const_pointer const_pointer; typedef typename allocator_type::reference reference; // lvalue of value_type. typedef typename allocator_type::const_reference const_reference; // const lvalue of value_type. typedef implementation-defined size_type; typedef implementation-defined difference_type; typedef implementation-defined iterator; typedef implementation-defined const_iterator; typedef implementation-defined local_iterator; typedef implementation-defined const_local_iterator; // construct/copy/destruct explicit unordered_set(size_type = implementation-defined, hasher const& = hasher(), key_equal const& = key_equal(), allocator_type const& = allocator_type()); template<typename InputIterator> unordered_set(InputIterator, InputIterator, size_type = implementation-defined, hasher const& = hasher(), key_equal const& = key_equal(), allocator_type const& = allocator_type()); unordered_set(unordered_set const&); explicit unordered_set(Allocator const&); unordered_set(unordered_set const&, Allocator const&); ~unordered_set(); unordered_set& operator=(unordered_set const&); allocator_type get_allocator() const; // size and capacity bool empty() const; size_type size() const; size_type max_size() const; // iterators iterator begin(); const_iterator begin() const; iterator end(); const_iterator end() const; const_iterator cbegin() const; const_iterator cend() const; // modifiers template<typename... Args> std::pair<iterator, bool> emplace(Args&&...); template<typename... Args> iterator emplace_hint(const_iterator, Args&&...); std::pair<iterator, bool> insert(value_type const&); iterator insert(const_iterator, value_type const&); template<typename InputIterator> void insert(InputIterator, InputIterator); iterator erase(const_iterator); size_type erase(key_type const&); iterator erase(const_iterator, const_iterator); void clear(); void swap(unordered_set&); // observers hasher hash_function() const; key_equal key_eq() const; // lookup iterator find(key_type const&); iterator find(key_type const&) const; size_type count(key_type const&) const; std::pair<iterator, iterator> equal_range(key_type const&); std::pair<const_iterator, const_iterator> equal_range(key_type const&) const; // bucket interface size_type bucket_count() const; size_type max_bucket_count() const; size_type bucket_size(size_type) const; size_type bucket(key_type const&) const; local_iterator begin(size_type); const_local_iterator begin(size_type) const; local_iterator end(size_type); const_local_iterator end(size_type) const; const_local_iterator cbegin(size_type) const; const_local_iterator cend(size_type); // hash policy float load_factor() const; float max_load_factor() const; void max_load_factor(float); void rehash(size_type); }; // Equality Comparisons template<typename Value, typename Hash, typename Pred, typename Alloc> bool operator==(unordered_set<Value, Hash, Pred, Alloc> const&, unordered_set<Value, Hash, Pred, Alloc> const&); template<typename Value, typename Hash, typename Pred, typename Alloc> bool operator!=(unordered_set<Value, Hash, Pred, Alloc> const&, unordered_set<Value, Hash, Pred, Alloc> const&); // swap template<typename Value, typename Hash, typename Pred, typename Alloc> void swap(unordered_set<Value, Hash, Pred, Alloc>&, unordered_set<Value, Hash, Pred, Alloc>&);
For the normative reference see chapter 23 of the working draft of the C++ standard [n2691].
Template Parameters
Value | Value must be Assignable and CopyConstructible |
Hash | A unary function object type that acts a hash function for a Value . It takes a single argument of type Value and returns a value of type std::size_t. |
Pred | A binary function object that implements an equivalence relation on values of type Value .
A binary function object that induces an equivalence relation on values of type Key.
It takes two arguments of type Key and returns a value of type bool. |
Alloc | An allocator whose value type is the same as the container's value type. |
The elements are organized into buckets. Keys with the same hash code are stored in the same bucket.
The number of buckets can be automatically increased by a call to insert, or as the result of calling rehash.
unordered_set
public
typestypedef implementation-defined size_type;
An unsigned integral type.
size_type can represent any non-negative value of difference_type.
typedef implementation-defined difference_type;
A signed integral type.
Is identical to the difference type of iterator and const_iterator.
typedef implementation-defined iterator;
A constant iterator whose value type is value_type.
Any iterator category except output iterator.
Convertible to const_iterator.
typedef implementation-defined const_iterator;
A constant iterator whose value type is value_type.
Any iterator category except output iterator.
typedef implementation-defined local_iterator;
An iterator with the same value type, difference type and pointer and reference type as iterator.
A local_iterator object can be used to iterate through a single bucket.
typedef implementation-defined const_local_iterator;
A constant iterator with the same value type, difference type and pointer and reference type as const_iterator.
A const_local_iterator object can be used to iterate through a single bucket.
unordered_set
public
construct/copy/destructexplicit unordered_set(size_type n = implementation-defined, hasher const& hf = hasher(), key_equal const& eq = key_equal(), allocator_type const& a = allocator_type());
Constructs an empty container with at least n buckets, using hf as the hash function, eq as the key equality predicate, a as the allocator and a maximum load factor of 1.0.
Postconditions: |
size() == 0 |
template<typename InputIterator> unordered_set(InputIterator f, InputIterator l, size_type n = implementation-defined, hasher const& hf = hasher(), key_equal const& eq = key_equal(), allocator_type const& a = allocator_type());
Constructs an empty container with at least n buckets, using hf as the hash function, eq as the key equality predicate, a as the allocator and a maximum load factor of 1.0 and inserts the elements from [f, l) into it.
unordered_set(unordered_set const&);
The copy constructor. Copies the contained elements, hash function, predicate, maximum load factor and allocator.
explicit unordered_set(Allocator const& a);
Constructs an empty container, using allocator a
.
unordered_set(unordered_set const& x, Allocator const& a);
Constructs an container, copying x
's contained elements, hash function, predicate, maximum load factor, but using allocator a
.
~unordered_set();
unordered_set& operator=(unordered_set const&);
The assignment operator. Copies the contained elements, hash function, predicate and maximum load factor but not the allocator.
allocator_type get_allocator() const;
unordered_set
iteratorsiterator begin(); const_iterator begin() const;
Returns: |
An iterator referring to the first element of the container, or if the container is empty the past-the-end value for the container. |
iterator end(); const_iterator end() const;
Returns: |
An iterator which refers to the past-the-end value for the container. |
const_iterator cbegin() const;
Returns: |
A constant iterator referring to the first element of the container, or if the container is empty the past-the-end value for the container. |
const_iterator cend() const;
Returns: |
A constant iterator which refers to the past-the-end value for the container. |
unordered_set
modifierstemplate<typename... Args> std::pair<iterator, bool> emplace(Args&&... args);
Inserts an object, constructed with the arguments args
, in the container if and only if there is no element in the container with an equivalent value.
Returns: |
The bool component of the return type is true if an insert took place. If an insert took place, then the iterator points to the newly inserted element. Otherwise, it points to the element with equivalent value. |
Throws: |
If an exception is thrown by an operation other than a call to |
Notes: |
Can invalidate iterators, but only if the insert causes the load factor to be greater to or equal to the maximum load factor. Pointers and references to elements are never invalidated. Only available on compilers with support for variadic template arguments and rvalue references. |
template<typename... Args> iterator emplace_hint(const_iterator hint, Args&&... args);
Inserts an object, constructed with the arguments args
, in the container if and only if there is no element in the container with an equivalent value.
hint is a suggestion to where the element should be inserted.
Returns: |
If an insert took place, then the iterator points to the newly inserted element. Otherwise, it points to the element with equivalent value. |
Throws: |
If an exception is thrown by an operation other than a call to |
Notes: |
The standard is fairly vague on the meaning of the hint. But the only practical way to use it, and the only way that Boost.Unordered supports is to point to an existing element with the same value. Can invalidate iterators, but only if the insert causes the load factor to be greater to or equal to the maximum load factor. Pointers and references to elements are never invalidated. Only available on compilers with support for variadic template arguments and rvalue references. |
std::pair<iterator, bool> insert(value_type const& obj);
Inserts obj in the container if and only if there is no element in the container with an equivalent value.
Returns: |
The bool component of the return type is true if an insert took place. If an insert took place, then the iterator points to the newly inserted element. Otherwise, it points to the element with equivalent value. |
Throws: |
If an exception is thrown by an operation other than a call to |
Notes: |
Can invalidate iterators, but only if the insert causes the load factor to be greater to or equal to the maximum load factor. Pointers and references to elements are never invalidated. |
iterator insert(const_iterator hint, value_type const& obj);
Inserts obj in the container if and only if there is no element in the container with an equivalent value.
hint is a suggestion to where the element should be inserted.
Returns: |
If an insert took place, then the iterator points to the newly inserted element. Otherwise, it points to the element with equivalent value. |
Throws: |
If an exception is thrown by an operation other than a call to |
Notes: |
The standard is fairly vague on the meaning of the hint. But the only practical way to use it, and the only way that Boost.Unordered supports is to point to an existing element with the same value. Can invalidate iterators, but only if the insert causes the load factor to be greater to or equal to the maximum load factor. Pointers and references to elements are never invalidated. |
template<typename InputIterator> void insert(InputIterator first, InputIterator last);
Inserts a range of elements into the container. Elements are inserted if and only if there is no element in the container with an equivalent value.
Throws: |
When inserting a single element, if an exception is thrown by an operation other than a call to |
Notes: |
Can invalidate iterators, but only if the insert causes the load factor to be greater to or equal to the maximum load factor. Pointers and references to elements are never invalidated. |
iterator erase(const_iterator position);
Erase the element pointed to by position
.
Returns: |
The iterator following |
Throws: |
Only throws an exception if it is thrown by In this implementation, this overload doesn't call either function object's methods so it is no throw, but this might not be true in other implementations. |
size_type erase(key_type const& k);
Erase all elements with key equivalent to k
.
Returns: |
The number of elements erased. |
Throws: |
Only throws an exception if it is thrown by |
iterator erase(const_iterator first, const_iterator last);
Erases the elements in the range from first
to last
.
Returns: |
The iterator following the erased elements - i.e. |
Throws: |
Only throws an exception if it is thrown by In this implementation, this overload doesn't call either function object's methods so it is no throw, but this might not be true in other implementations. |
void clear();
Erases all elements in the container.
Postconditions: |
|
Throws: |
Never throws an exception. |
void swap(unordered_set&);
Throws: |
If the allocators are equal, doesn't throw an exception unless it is thrown by the copy constructor or copy assignment operator of |
Notes: |
For a discussion of the behavior when allocators aren't equal see the implementation details. |
unordered_set
lookupiterator find(key_type const& k); iterator find(key_type const& k) const;
Returns: |
An iterator pointing to an element with key equivalent to |
size_type count(key_type const& k) const;
Returns: |
The number of elements with key equivalent to |
std::pair<iterator, iterator> equal_range(key_type const& k); std::pair<const_iterator, const_iterator> equal_range(key_type const& k) const;
Returns: |
A range containing all elements with key equivalent to |
unordered_set
bucket interfacesize_type bucket_count() const;
Returns: |
The number of buckets. |
size_type max_bucket_count() const;
Returns: |
An upper bound on the number of buckets. |
size_type bucket_size(size_type n) const;
Requires: |
|
Returns: |
The number of elements in bucket |
size_type bucket(key_type const& k) const;
Returns: |
The index of the bucket which would contain an element with key |
Postconditions: |
The return value is less than |
local_iterator begin(size_type n); const_local_iterator begin(size_type n) const;
Requires: |
|
Returns: |
A local iterator pointing the first element in the bucket with index |
local_iterator end(size_type n); const_local_iterator end(size_type n) const;
Requires: |
|
Returns: |
A local iterator pointing the 'one past the end' element in the bucket with index |
const_local_iterator cbegin(size_type n) const;
Requires: |
|
Returns: |
A constant local iterator pointing the first element in the bucket with index |
const_local_iterator cend(size_type n);
Requires: |
|
Returns: |
A constant local iterator pointing the 'one past the end' element in the bucket with index |
unordered_set
hash policyfloat load_factor() const;
Returns: |
The average number of elements per bucket. |
float max_load_factor() const;
Returns: |
Returns the current maximum load factor. |
void max_load_factor(float z);
Effects: |
Changes the container's maximum load factor, using |
void rehash(size_type n);
Changes the number of buckets so that there at least n
buckets, and so that the load factor is less than the maximum load factor.
Invalidates iterators, and changes the order of elements. Pointers and references to elements are not invalidated.
Throws: |
The function has no effect if an exception is thrown, unless it is thrown by the container's hash function or comparison function. |
unordered_set
Equality Comparisonstemplate<typename Value, typename Hash, typename Pred, typename Alloc> bool operator==(unordered_set<Value, Hash, Pred, Alloc> const& x, unordered_set<Value, Hash, Pred, Alloc> const& y);
Notes: |
This is a boost extension. Behavior is undefined if the two containers don't have equivalent equality predicates. |
template<typename Value, typename Hash, typename Pred, typename Alloc> bool operator!=(unordered_set<Value, Hash, Pred, Alloc> const& x, unordered_set<Value, Hash, Pred, Alloc> const& y);
Notes: |
This is a boost extension. Behavior is undefined if the two containers don't have equivalent equality predicates. |
unordered_set
swaptemplate<typename Value, typename Hash, typename Pred, typename Alloc> void swap(unordered_set<Value, Hash, Pred, Alloc>& x, unordered_set<Value, Hash, Pred, Alloc>& y);
Effects: |
|
Throws: |
If the allocators are equal, doesn't throw an exception unless it is thrown by the copy constructor or copy assignment operator of |
Notes: |
For a discussion of the behavior when allocators aren't equal see the implementation details. |