boost::hash<Value>
std::equal_to<Value>
std::allocator<Value>

An unordered associative container that stores unique values.

Template Parameters

Value | `Value` must be `Erasable` from the container (i.e. `allocator_traits` can `destroy` it).
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 `Value`. It takes two arguments of type `Value` 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.

Value
Value
Hash
Pred
Alloc
typename allocator_type::pointer

`value_type*` if `allocator_type::pointer` is not defined.

typename allocator_type::const_pointer

`boost::pointer_to_other<pointer, value_type>::type` if `allocator_type::const_pointer` is not defined.

value_type&

lvalue of value_type.

value_type const&

const lvalue of value_type.

implementation-defined

An unsigned integral type.

size_type can represent any non-negative value of difference_type.

implementation-defined

A signed integral type.

Is identical to the difference type of iterator and const_iterator.

implementation-defined

A constant iterator whose value type is value_type.

The iterator category is at least a forward iterator.

Convertible to const_iterator.

implementation-defined

A constant iterator whose value type is value_type.

The iterator category is at least a forward iterator.

implementation-defined

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.

implementation-defined

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.

implementation-defined

See `node_handle_set` for details.

implementation-defined Structure returned by inserting `node_type`.
size
() == 0

Constructs an empty container using hasher() as the hash function, key_equal() as the key equality predicate, allocator_type() as the allocator and a maximum load factor of 1.0.

If the defaults are used, `hasher`, `key_equal` and `allocator_type` need to be `DefaultConstructible`.

size_type
hasher const&
hasher()
key_equal const&
key_equal()
allocator_type const&
allocator_type()
size
() == 0

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.

If the defaults are used, `hasher`, `key_equal` and `allocator_type` need to be `DefaultConstructible`.

InputIterator
InputIterator
size_type
implementation-defined
hasher const&
hasher()
key_equal const&
key_equal()
allocator_type const&
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.

If the defaults are used, `hasher`, `key_equal` and `allocator_type` need to be `DefaultConstructible`.

unordered_set const&

The copy constructor. Copies the contained elements, hash function, predicate, maximum load factor and allocator.

If `Allocator::select_on_container_copy_construction` exists and has the right signature, the allocator will be constructed from its result.

`value_type` is copy constructible

unordered_set &&

The move constructor.

This is implemented using Boost.Move.

`value_type` is move constructible.

On compilers without rvalue reference support the emulation does not support moving without calling `boost::move` if `value_type` is not copyable. So, for example, you can't return the container from a function.

Allocator const&

Constructs an empty container, using allocator `a`.

unordered_set const&
Allocator const&

Constructs an container, copying `x`'s contained elements, hash function, predicate, maximum load factor, but using allocator `a`.

unordered_set &&
Allocator const&

Construct a container moving `x`'s contained elements, and having the hash function, predicate and maximum load factor, but using allocate `a`.

This is implemented using Boost.Move.

`value_type` is move insertable.

initializer_list<value_type>
size_type
implementation-defined
hasher const&
hasher()
key_equal const&
key_equal()
allocator_type const&
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 `il` into it.

If the defaults are used, `hasher`, `key_equal` and `allocator_type` need to be `DefaultConstructible`.

size_type
allocator_type const&
size
() == 0

Constructs an empty container with at least `n` buckets, using `hf` as the hash function, the default hash function and key equality predicate, `a` as the allocator and a maximum load factor of 1.0.

`hasher` and `key_equal` need to be `DefaultConstructible`.

size_type
hasher const&
allocator_type const&
size
() == 0

Constructs an empty container with at least `n` buckets, using `hf` as the hash function, the default key equality predicate, `a` as the allocator and a maximum load factor of 1.0.

`key_equal` needs to be `DefaultConstructible`.

InputIterator
InputIterator
size_type
allocator_type const&

Constructs an empty container with at least `n` buckets, using `a` as the allocator, with the default hash function and key equality predicate and a maximum load factor of 1.0 and inserts the elements from [f, l) into it.

`hasher`, `key_equal` need to be `DefaultConstructible`.

InputIterator
InputIterator
size_type
hasher const&
allocator_type const&

Constructs an empty container with at least `n` buckets, using `hf` as the hash function, `a` as the allocator, with the default key equality predicate and a maximum load factor of 1.0 and inserts the elements from [f, l) into it.

`key_equal` needs to be `DefaultConstructible`.

The destructor is applied to every element, and all memory is deallocated

unordered_set const&
unordered_set&

The assignment operator. Copies the contained elements, hash function, predicate and maximum load factor but not the allocator.

If `Alloc::propagate_on_container_copy_assignment` exists and `Alloc::propagate_on_container_copy_assignment::value` is true, the allocator is overwritten, if not the copied elements are created using the existing allocator.

`value_type` is copy constructible

unordered_set &&
unordered_set&

The move assignment operator.

If `Alloc::propagate_on_container_move_assignment` exists and `Alloc::propagate_on_container_move_assignment::value` is true, the allocator is overwritten, if not the moved elements are created using the existing allocator.

On compilers without rvalue references, this is emulated using Boost.Move. Note that on some compilers the copy assignment operator may be used in some circumstances.

`value_type` is move constructible.

initializer_list<value_type>
unordered_set&

Assign from values in initializer list. All existing elements are either overwritten by the new elements or destroyed.

`value_type` is `CopyInsertable` into the container and `CopyAssignable`.

allocator_type
bool ``size`() == 0`
size_type `std::distance(`begin`(), `end`())`
size_type ``size`()` of the largest possible container.
iterator
const_iterator
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
const_iterator
An iterator which refers to the past-the-end value for the container.
const_iterator 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 A constant iterator which refers to the past-the-end value for the container.
Args&&
std::pair<iterator, bool>

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.

`value_type` is `EmplaceConstructible` into `X` from `args`.

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.

If an exception is thrown by an operation other than a call to `hasher` the function has no effect.

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.

If the compiler doesn't support variadic template arguments or rvalue references, this is emulated for up to 10 arguments, with no support for rvalue references or move semantics.

Since existing `std::pair` implementations don't support `std::piecewise_construct` this emulates it, but using `boost::unordered::piecewise_construct`.

const_iterator
Args&&
iterator

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.

`value_type` is `EmplaceConstructible` into `X` from `args`.

If an insert took place, then the iterator points to the newly inserted element. Otherwise, it points to the element with equivalent value.

If an exception is thrown by an operation other than a call to `hasher` the function has no effect.

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.

If the compiler doesn't support variadic template arguments or rvalue references, this is emulated for up to 10 arguments, with no support for rvalue references or move semantics.

Since existing `std::pair` implementations don't support `std::piecewise_construct` this emulates it, but using `boost::unordered::piecewise_construct`.

value_type const&
std::pair<iterator, bool>

Inserts `obj` in the container if and only if there is no element in the container with an equivalent value.

`value_type` is `CopyInsertable`.

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.

If an exception is thrown by an operation other than a call to `hasher` the function has no effect.

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.

value_type&&
std::pair<iterator, bool>

Inserts `obj` in the container if and only if there is no element in the container with an equivalent value.

`value_type` is `MoveInsertable`.

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.

If an exception is thrown by an operation other than a call to `hasher` the function has no effect.

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.

const_iterator
value_type const&
iterator

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.

`value_type` is `CopyInsertable`.

If an insert took place, then the iterator points to the newly inserted element. Otherwise, it points to the element with equivalent value.

If an exception is thrown by an operation other than a call to `hasher` the function has no effect.

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.

const_iterator
value_type&&
iterator

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.

`value_type` is `MoveInsertable`.

If an insert took place, then the iterator points to the newly inserted element. Otherwise, it points to the element with equivalent value.

If an exception is thrown by an operation other than a call to `hasher` the function has no effect.

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.

InputIterator
InputIterator
void

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.

`value_type` is `EmplaceConstructible` into `X` from `*first`.

When inserting a single element, if an exception is thrown by an operation other than a call to `hasher` the function has no effect.

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.

initializer_list<value_type>
void

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.

`value_type` is `EmplaceConstructible` into `X` from `*first`.

When inserting a single element, if an exception is thrown by an operation other than a call to `hasher` the function has no effect.

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.

initializer_list<value_type>
void

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.

`value_type` is `EmplaceConstructible` into `X` from `*first`.

When inserting a single element, if an exception is thrown by an operation other than a call to `hasher` the function has no effect.

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.

const_iterator
node_type

Removes the element pointed to by `position`.

A `node_type` owning the element.

In C++17 a node extracted using this method can be inserted into a compatible `unordered_multiset`, but that is not supported yet.

key_type const&
node_type

Removes an element with key equivalent to `k`.

A `node_type` owning the element if found, otherwise an empty `node_type`.

Only throws an exception if it is thrown by `hasher` or `key_equal`.

In C++17 a node extracted using this method can be inserted into a compatible `unordered_multiset`, but that is not supported yet.

node_type&&
insert_return_type

If `nh` is empty, has no affect.

Otherwise inserts the element owned by `nh` if and only if there is no element in the container with an equivalent value.

`nh` is empty or `nh.get_allocator()` is equal to the container's allocator.

If `nh` was empty, returns an `insert_return_type` with: `inserted` equal to `false`, `position` equal to `end()` and `node` empty.

Otherwise if there was already an element with an equivalent key, returns an `insert_return_type` with: `inserted` equal to `false`, `position` pointing to a matching element and `node` contains the node from `nh`.

Otherwise if the insertion succeeded, returns an `insert_return_type` with: `inserted` equal to `true`, `position` pointing to the newly inserted element and `node` empty.

If an exception is thrown by an operation other than a call to `hasher` the function has no effect.

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.

In C++17 this can be used to insert a node extracted from a compatible `unordered_multiset`, but that is not supported yet.

const_iterator
node_type&&
iterator

If `nh` is empty, has no affect.

Otherwise inserts the element owned by `nh` if and only if there is no element in the container with an equivalent value.

If there is already an element in the container with an equivalent value has no effect on `nh` (i.e. `nh` still contains the node.)

hint is a suggestion to where the element should be inserted.

`nh` is empty or `nh.get_allocator()` is equal to the container's allocator.

If `nh` was empty returns `end()`.

If there was already an element in the container with an equivalent value returns an iterator pointing to that.

Otherwise returns an iterator pointing to the newly inserted element.

If an exception is thrown by an operation other than a call to `hasher` the function has no effect.

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.

In C++17 this can be used to insert a node extracted from a compatible `unordered_multiset`, but that is not supported yet.

const_iterator
iterator

Erase the element pointed to by `position`.

The iterator following `position` before the erasure.

Only throws an exception if it is thrown by `hasher` or `key_equal`.

In older versions this could be inefficient because it had to search through several buckets to find the position of the returned iterator. The data structure has been changed so that this is no longer the case, and the alternative erase methods have been deprecated.

key_type const&
size_type

Erase all elements with key equivalent to `k`.

The number of elements erased.

Only throws an exception if it is thrown by `hasher` or `key_equal`.

const_iterator
const_iterator
iterator

Erases the elements in the range from `first` to `last`.

The iterator following the erased elements - i.e. `last`.

Only throws an exception if it is thrown by `hasher` or `key_equal`.

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.

const_iterator
void

Erase the element pointed to by `position`.

Only throws an exception if it is thrown by `hasher` or `key_equal`.

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.

This method was implemented because returning an iterator to the next element from `erase` was expensive, but the container has been redesigned so that is no longer the case. So this method is now deprecated.

const_iterator
void

Erase the element pointed to by `position`.

Only throws an exception if it is thrown by `hasher` or `key_equal`.

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.

This method was implemented because returning an iterator to the next element from `erase` was expensive, but the container has been redesigned so that is no longer the case. So this method is now deprecated.

void

Erases all elements in the container.

``size`() == 0`

Never throws an exception.

unordered_set&
void

Swaps the contents of the container with the parameter.

If `Allocator::propagate_on_container_swap` is declared and `Allocator::propagate_on_container_swap::value` is true then the containers' allocators are swapped. Otherwise, swapping with unequal allocators results in undefined behavior.

Doesn't throw an exception unless it is thrown by the copy constructor or copy assignment operator of `key_equal` or `hasher`.

The exception specifications aren't quite the same as the C++11 standard, as the equality predieate and hash function are swapped using their copy constructors.

unordered_set<Value, H2, P2, Alloc>&

Does not support merging with a compatible `unordered_multiset` yet.

unordered_set<Value, H2, P2, Alloc>&&

Does not support merging with a compatible `unordered_multiset` yet.

hasher The container's hash function.
key_equal The container's key equality predicate.
key_type const&
iterator
key_type const&
const_iterator
CompatibleKey const&
CompatibleHash const&
CompatiblePredicate const&
iterator
CompatibleKey const&
CompatibleHash const&
CompatiblePredicate const&
const_iterator

An iterator pointing to an element with key equivalent to `k`, or `b.end()` if no such element exists.

The templated overloads are a non-standard extensions which allows you to use a compatible hash function and equality predicate for a key of a different type in order to avoid an expensive type cast. In general, its use is not encouraged.

key_type const&
size_type

The number of elements with key equivalent to `k`.

key_type const&
std::pair<iterator, iterator>
key_type const&
std::pair<const_iterator, const_iterator>

A range containing all elements with key equivalent to `k`. If the container doesn't container any such elements, returns `std::make_pair(`b.end`(),`b.end`())`.

size_type

The number of buckets.

size_type

An upper bound on the number of buckets.

size_type
size_type

`n < `bucket_count`()`

The number of elements in bucket `n`.

key_type const&
size_type

The index of the bucket which would contain an element with key `k`.

The return value is less than `bucket_count()`

size_type
local_iterator
size_type
const_local_iterator

`n` shall be in the range `[0, bucket_count())`.

A local iterator pointing the first element in the bucket with index `n`.

size_type
local_iterator
size_type
const_local_iterator

`n` shall be in the range `[0, bucket_count())`.

A local iterator pointing the 'one past the end' element in the bucket with index `n`.

size_type
const_local_iterator

`n` shall be in the range `[0, bucket_count())`.

A constant local iterator pointing the first element in the bucket with index `n`.

size_type
const_local_iterator

`n` shall be in the range `[0, bucket_count())`.

A constant local iterator pointing the 'one past the end' element in the bucket with index `n`.

float

The average number of elements per bucket.

float

Returns the current maximum load factor.

float
void

Changes the container's maximum load factor, using `z` as a hint.

size_type
void

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.

The function has no effect if an exception is thrown, unless it is thrown by the container's hash function or comparison function.

size_type
void

Invalidates iterators, and changes the order of elements. Pointers and references to elements are not invalidated.

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<Value, Hash, Pred, Alloc> const&
unordered_set<Value, Hash, Pred, Alloc> const&
bool

Return `true` if `x.size() == y.size` and for every element in `x`, there is an element in `y` with the same for the same key, with an equal value (using `operator==` to compare the value types).

The behavior of this function was changed to match the C++11 standard in Boost 1.48.

Behavior is undefined if the two containers don't have equivalent equality predicates.

unordered_set<Value, Hash, Pred, Alloc> const&
unordered_set<Value, Hash, Pred, Alloc> const&
bool

Return `false` if `x.size() == y.size` and for every element in `x`, there is an element in `y` with the same for the same key, with an equal value (using `operator==` to compare the value types).

The behavior of this function was changed to match the C++11 standard in Boost 1.48.

Behavior is undefined if the two containers don't have equivalent equality predicates.

unordered_set<Value, Hash, Pred, Alloc>&
unordered_set<Value, Hash, Pred, Alloc>&
void

`x.swap(y)`

Swaps the contents of `x` and `y`.

If `Allocator::propagate_on_container_swap` is declared and `Allocator::propagate_on_container_swap::value` is true then the containers' allocators are swapped. Otherwise, swapping with unequal allocators results in undefined behavior.

Doesn't throw an exception unless it is thrown by the copy constructor or copy assignment operator of `key_equal` or `hasher`.

The exception specifications aren't quite the same as the C++11 standard, as the equality predieate and hash function are swapped using their copy constructors.

boost::hash<Value>
std::equal_to<Value>
std::allocator<Value>

An unordered associative container that stores values. The same key can be stored multiple times.

Template Parameters

Value | `Value` must be `Erasable` from the container (i.e. `allocator_traits` can `destroy` it).
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 `Value`. It takes two arguments of type `Value` 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 and elements with equivalent keys are stored next to each other.

The number of buckets can be automatically increased by a call to insert, or as the result of calling rehash.

Value
Value
Hash
Pred
Alloc
typename allocator_type::pointer

`value_type*` if `allocator_type::pointer` is not defined.

typename allocator_type::const_pointer

`boost::pointer_to_other<pointer, value_type>::type` if `allocator_type::const_pointer` is not defined.

value_type&

lvalue of value_type.

value_type const&

const lvalue of value_type.

implementation-defined

An unsigned integral type.

size_type can represent any non-negative value of difference_type.

implementation-defined

A signed integral type.

Is identical to the difference type of iterator and const_iterator.

implementation-defined

A constant iterator whose value type is value_type.

The iterator category is at least a forward iterator.

Convertible to const_iterator.

implementation-defined

A constant iterator whose value type is value_type.

The iterator category is at least a forward iterator.

implementation-defined

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.

implementation-defined

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.

implementation-defined

See `node_handle_set` for details.

size
() == 0

Constructs an empty container using hasher() as the hash function, key_equal() as the key equality predicate, allocator_type() as the allocator and a maximum load factor of 1.0.

If the defaults are used, `hasher`, `key_equal` and `allocator_type` need to be `DefaultConstructible`.

size_type
hasher const&
hasher()
key_equal const&
key_equal()
allocator_type const&
allocator_type()
size
() == 0

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.

If the defaults are used, `hasher`, `key_equal` and `allocator_type` need to be `DefaultConstructible`.

InputIterator
InputIterator
size_type
implementation-defined
hasher const&
hasher()
key_equal const&
key_equal()
allocator_type const&
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.

If the defaults are used, `hasher`, `key_equal` and `allocator_type` need to be `DefaultConstructible`.

unordered_multiset const&

The copy constructor. Copies the contained elements, hash function, predicate, maximum load factor and allocator.

If `Allocator::select_on_container_copy_construction` exists and has the right signature, the allocator will be constructed from its result.

`value_type` is copy constructible

unordered_multiset &&

The move constructor.

This is implemented using Boost.Move.

`value_type` is move constructible.

On compilers without rvalue reference support the emulation does not support moving without calling `boost::move` if `value_type` is not copyable. So, for example, you can't return the container from a function.

Allocator const&

Constructs an empty container, using allocator `a`.

unordered_multiset const&
Allocator const&

Constructs an container, copying `x`'s contained elements, hash function, predicate, maximum load factor, but using allocator `a`.

unordered_multiset &&
Allocator const&

Construct a container moving `x`'s contained elements, and having the hash function, predicate and maximum load factor, but using allocate `a`.

This is implemented using Boost.Move.

`value_type` is move insertable.

initializer_list<value_type>
size_type
implementation-defined
hasher const&
hasher()
key_equal const&
key_equal()
allocator_type const&
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 `il` into it.

If the defaults are used, `hasher`, `key_equal` and `allocator_type` need to be `DefaultConstructible`.

size_type
allocator_type const&
size
() == 0

Constructs an empty container with at least `n` buckets, using `hf` as the hash function, the default hash function and key equality predicate, `a` as the allocator and a maximum load factor of 1.0.

`hasher` and `key_equal` need to be `DefaultConstructible`.

size_type
hasher const&
allocator_type const&
size
() == 0

Constructs an empty container with at least `n` buckets, using `hf` as the hash function, the default key equality predicate, `a` as the allocator and a maximum load factor of 1.0.

`key_equal` needs to be `DefaultConstructible`.

InputIterator
InputIterator
size_type
allocator_type const&

Constructs an empty container with at least `n` buckets, using `a` as the allocator, with the default hash function and key equality predicate and a maximum load factor of 1.0 and inserts the elements from [f, l) into it.

`hasher`, `key_equal` need to be `DefaultConstructible`.

InputIterator
InputIterator
size_type
hasher const&
allocator_type const&

Constructs an empty container with at least `n` buckets, using `hf` as the hash function, `a` as the allocator, with the default key equality predicate and a maximum load factor of 1.0 and inserts the elements from [f, l) into it.

`key_equal` needs to be `DefaultConstructible`.

The destructor is applied to every element, and all memory is deallocated

unordered_multiset const&
unordered_multiset&

The assignment operator. Copies the contained elements, hash function, predicate and maximum load factor but not the allocator.

If `Alloc::propagate_on_container_copy_assignment` exists and `Alloc::propagate_on_container_copy_assignment::value` is true, the allocator is overwritten, if not the copied elements are created using the existing allocator.

`value_type` is copy constructible

unordered_multiset &&
unordered_multiset&

The move assignment operator.

If `Alloc::propagate_on_container_move_assignment` exists and `Alloc::propagate_on_container_move_assignment::value` is true, the allocator is overwritten, if not the moved elements are created using the existing allocator.

On compilers without rvalue references, this is emulated using Boost.Move. Note that on some compilers the copy assignment operator may be used in some circumstances.

`value_type` is move constructible.

initializer_list<value_type>
unordered_multiset&

Assign from values in initializer list. All existing elements are either overwritten by the new elements or destroyed.

`value_type` is `CopyInsertable` into the container and `CopyAssignable`.

allocator_type
bool ``size`() == 0`
size_type `std::distance(`begin`(), `end`())`
size_type ``size`()` of the largest possible container.
iterator
const_iterator
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
const_iterator
An iterator which refers to the past-the-end value for the container.
const_iterator 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 A constant iterator which refers to the past-the-end value for the container.
Args&&
iterator

Inserts an object, constructed with the arguments `args`, in the container.

`value_type` is `EmplaceConstructible` into `X` from `args`.

An iterator pointing to the inserted element.

If an exception is thrown by an operation other than a call to `hasher` the function has no effect.

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.

If the compiler doesn't support variadic template arguments or rvalue references, this is emulated for up to 10 arguments, with no support for rvalue references or move semantics.

Since existing `std::pair` implementations don't support `std::piecewise_construct` this emulates it, but using `boost::unordered::piecewise_construct`.

const_iterator
Args&&
iterator

Inserts an object, constructed with the arguments `args`, in the container.

`hint` is a suggestion to where the element should be inserted.

`value_type` is `EmplaceConstructible` into `X` from `args`.

An iterator pointing to the inserted element.

If an exception is thrown by an operation other than a call to `hasher` the function has no effect.

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.

If the compiler doesn't support variadic template arguments or rvalue references, this is emulated for up to 10 arguments, with no support for rvalue references or move semantics.

Since existing `std::pair` implementations don't support `std::piecewise_construct` this emulates it, but using `boost::unordered::piecewise_construct`.

value_type const&
iterator

Inserts `obj` in the container.

`value_type` is `CopyInsertable`.

An iterator pointing to the inserted element.

If an exception is thrown by an operation other than a call to `hasher` the function has no effect.

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.

value_type&&
iterator

Inserts `obj` in the container.

`value_type` is `MoveInsertable`.

An iterator pointing to the inserted element.

If an exception is thrown by an operation other than a call to `hasher` the function has no effect.

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.

const_iterator
value_type const&
iterator

Inserts `obj` in the container.

hint is a suggestion to where the element should be inserted.

`value_type` is `CopyInsertable`.

An iterator pointing to the inserted element.

If an exception is thrown by an operation other than a call to `hasher` the function has no effect.

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.

const_iterator
value_type&&
iterator

Inserts `obj` in the container.

hint is a suggestion to where the element should be inserted.

`value_type` is `MoveInsertable`.

An iterator pointing to the inserted element.

If an exception is thrown by an operation other than a call to `hasher` the function has no effect.

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.

InputIterator
InputIterator
void

Inserts a range of elements into the container.

`value_type` is `EmplaceConstructible` into `X` from `*first`.

When inserting a single element, if an exception is thrown by an operation other than a call to `hasher` the function has no effect.

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.

initializer_list<value_type>
void

Inserts a range of elements into the container.

`value_type` is `EmplaceConstructible` into `X` from `*first`.

When inserting a single element, if an exception is thrown by an operation other than a call to `hasher` the function has no effect.

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.

initializer_list<value_type>
void

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.

`value_type` is `EmplaceConstructible` into `X` from `*first`.

When inserting a single element, if an exception is thrown by an operation other than a call to `hasher` the function has no effect.

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.

const_iterator
node_type

Removes the element pointed to by `position`.

A `node_type` owning the element.

In C++17 a node extracted using this method can be inserted into a compatible `unordered_set`, but that is not supported yet.

key_type const&
node_type

Removes an element with key equivalent to `k`.

A `node_type` owning the element if found, otherwise an empty `node_type`.

Only throws an exception if it is thrown by `hasher` or `key_equal`.

In C++17 a node extracted using this method can be inserted into a compatible `unordered_set`, but that is not supported yet.

node_type&&
iterator

If `nh` is empty, has no affect.

Otherwise inserts the element owned by `nh`

`nh` is empty or `nh.get_allocator()` is equal to the container's allocator.

If `nh` was empty, returns `end()`.

Otherwise returns an iterator pointing to the newly inserted element.

If an exception is thrown by an operation other than a call to `hasher` the function has no effect.

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.

In C++17 this can be used to insert a node extracted from a compatible `unordered_set`, but that is not supported yet.

const_iterator
node_type&&
iterator

If `nh` is empty, has no affect.

Otherwise inserts the element owned by `nh`

hint is a suggestion to where the element should be inserted.

`nh` is empty or `nh.get_allocator()` is equal to the container's allocator.

If `nh` was empty, returns `end()`.

Otherwise returns an iterator pointing to the newly inserted element.

If an exception is thrown by an operation other than a call to `hasher` the function has no effect.

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.

In C++17 this can be used to insert a node extracted from a compatible `unordered_set`, but that is not supported yet.

const_iterator
iterator

Erase the element pointed to by `position`.

The iterator following `position` before the erasure.

Only throws an exception if it is thrown by `hasher` or `key_equal`.

In older versions this could be inefficient because it had to search through several buckets to find the position of the returned iterator. The data structure has been changed so that this is no longer the case, and the alternative erase methods have been deprecated.

key_type const&
size_type

Erase all elements with key equivalent to `k`.

The number of elements erased.

Only throws an exception if it is thrown by `hasher` or `key_equal`.

const_iterator
const_iterator
iterator

Erases the elements in the range from `first` to `last`.

The iterator following the erased elements - i.e. `last`.

Only throws an exception if it is thrown by `hasher` or `key_equal`.

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.

const_iterator
void

Erase the element pointed to by `position`.

Only throws an exception if it is thrown by `hasher` or `key_equal`.

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.

This method was implemented because returning an iterator to the next element from `erase` was expensive, but the container has been redesigned so that is no longer the case. So this method is now deprecated.

const_iterator
void

Erase the element pointed to by `position`.

Only throws an exception if it is thrown by `hasher` or `key_equal`.

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.

This method was implemented because returning an iterator to the next element from `erase` was expensive, but the container has been redesigned so that is no longer the case. So this method is now deprecated.

void

Erases all elements in the container.

``size`() == 0`

Never throws an exception.

unordered_multiset&
void

Swaps the contents of the container with the parameter.

If `Allocator::propagate_on_container_swap` is declared and `Allocator::propagate_on_container_swap::value` is true then the containers' allocators are swapped. Otherwise, swapping with unequal allocators results in undefined behavior.

Doesn't throw an exception unless it is thrown by the copy constructor or copy assignment operator of `key_equal` or `hasher`.

The exception specifications aren't quite the same as the C++11 standard, as the equality predieate and hash function are swapped using their copy constructors.

unordered_multiset<Value, H2, P2, Alloc>&

Does not support merging with a compatible `unordered_set` yet.

unordered_multiset<Value, H2, P2, Alloc>&&

Does not support merging with a compatible `unordered_set` yet.

hasher The container's hash function.
key_equal The container's key equality predicate.
key_type const&
iterator
key_type const&
const_iterator
CompatibleKey const&
CompatibleHash const&
CompatiblePredicate const&
iterator
CompatibleKey const&
CompatibleHash const&
CompatiblePredicate const&
const_iterator

An iterator pointing to an element with key equivalent to `k`, or `b.end()` if no such element exists.

The templated overloads are a non-standard extensions which allows you to use a compatible hash function and equality predicate for a key of a different type in order to avoid an expensive type cast. In general, its use is not encouraged.

key_type const&
size_type

The number of elements with key equivalent to `k`.

key_type const&
std::pair<iterator, iterator>
key_type const&
std::pair<const_iterator, const_iterator>

A range containing all elements with key equivalent to `k`. If the container doesn't container any such elements, returns `std::make_pair(`b.end`(),`b.end`())`.

size_type

The number of buckets.

size_type

An upper bound on the number of buckets.

size_type
size_type

`n < `bucket_count`()`

The number of elements in bucket `n`.

key_type const&
size_type

The index of the bucket which would contain an element with key `k`.

The return value is less than `bucket_count()`

size_type
local_iterator
size_type
const_local_iterator

`n` shall be in the range `[0, bucket_count())`.

A local iterator pointing the first element in the bucket with index `n`.

size_type
local_iterator
size_type
const_local_iterator

`n` shall be in the range `[0, bucket_count())`.

A local iterator pointing the 'one past the end' element in the bucket with index `n`.

size_type
const_local_iterator

`n` shall be in the range `[0, bucket_count())`.

A constant local iterator pointing the first element in the bucket with index `n`.

size_type
const_local_iterator

`n` shall be in the range `[0, bucket_count())`.

A constant local iterator pointing the 'one past the end' element in the bucket with index `n`.

float

The average number of elements per bucket.

float

Returns the current maximum load factor.

float
void

Changes the container's maximum load factor, using `z` as a hint.

size_type
void

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.

The function has no effect if an exception is thrown, unless it is thrown by the container's hash function or comparison function.

size_type
void

Invalidates iterators, and changes the order of elements. Pointers and references to elements are not invalidated.

The function has no effect if an exception is thrown, unless it is thrown by the container's hash function or comparison function.

unordered_multiset<Value, Hash, Pred, Alloc> const&
unordered_multiset<Value, Hash, Pred, Alloc> const&
bool

Return `true` if `x.size() == y.size` and for every equivalent key group in `x`, there is a group in `y` for the same key, which is a permutation (using `operator==` to compare the value types).

The behavior of this function was changed to match the C++11 standard in Boost 1.48.

Behavior is undefined if the two containers don't have equivalent equality predicates.

unordered_multiset<Value, Hash, Pred, Alloc> const&
unordered_multiset<Value, Hash, Pred, Alloc> const&
bool

Return `false` if `x.size() == y.size` and for every equivalent key group in `x`, there is a group in `y` for the same key, which is a permutation (using `operator==` to compare the value types).

The behavior of this function was changed to match the C++11 standard in Boost 1.48.

Behavior is undefined if the two containers don't have equivalent equality predicates.

unordered_multiset<Value, Hash, Pred, Alloc>&
unordered_multiset<Value, Hash, Pred, Alloc>&
void

`x.swap(y)`

Swaps the contents of `x` and `y`.

If `Allocator::propagate_on_container_swap` is declared and `Allocator::propagate_on_container_swap::value` is true then the containers' allocators are swapped. Otherwise, swapping with unequal allocators results in undefined behavior.

Doesn't throw an exception unless it is thrown by the copy constructor or copy assignment operator of `key_equal` or `hasher`.

The exception specifications aren't quite the same as the C++11 standard, as the equality predieate and hash function are swapped using their copy constructors.

An object that owns a single element extracted from an `unordered_set` or an `unordered_multiset`, that can then be inserted into a compatible container type.

The name and template parameters of this type are implementation defined, and should be obtained using the `node_type` member typedef from the appropriate container.

typename Container::value_type>
typename Container::allocator_type>
node_handle_set &&
node_handle_set&&
node_handle_set&
value_type&
allocator_type
bool
node_handle_set&
void

In C++17 is also `noexcept` if `ator_traits::is_always_equal::value` is true. But we don't support that trait yet.

node_handle_set<ImplementationDefined>&
node_handle_set<ImplementationDefined>&
void

`x.swap(y)`

boost::hash<Key>
std::equal_to<Key>
std::allocator<std::pair<Key const, Mapped>>

An unordered associative container that associates unique keys with another value.

Template Parameters

Key | `Key` must be `Erasable` from the container (i.e. `allocator_traits` can `destroy` it).
Mapped | `Mapped` must be `Erasable` from the container (i.e. `allocator_traits` can `destroy` it).
Hash | A unary function object type that acts a hash function for a `Key`. It takes a single argument of type `Key` and returns a value of type std::size_t.
Pred | A binary function object that implements an equivalence relation on values of type `Key`. 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.

Key
std::pair<Key const, Mapped>
Mapped
Hash
Pred
Alloc
typename allocator_type::pointer

`value_type*` if `allocator_type::pointer` is not defined.

typename allocator_type::const_pointer

`boost::pointer_to_other<pointer, value_type>::type` if `allocator_type::const_pointer` is not defined.

value_type&

lvalue of value_type.

value_type const&

const lvalue of value_type.

implementation-defined

An unsigned integral type.

size_type can represent any non-negative value of difference_type.

implementation-defined

A signed integral type.

Is identical to the difference type of iterator and const_iterator.

implementation-defined

An iterator whose value type is value_type.

The iterator category is at least a forward iterator.

Convertible to const_iterator.

implementation-defined

A constant iterator whose value type is value_type.

The iterator category is at least a forward iterator.

implementation-defined

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.

implementation-defined

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.

implementation-defined

See `node_handle_map` for details.

implementation-defined Structure returned by inserting `node_type`.
size
() == 0

Constructs an empty container using hasher() as the hash function, key_equal() as the key equality predicate, allocator_type() as the allocator and a maximum load factor of 1.0.

If the defaults are used, `hasher`, `key_equal` and `allocator_type` need to be `DefaultConstructible`.

size_type
hasher const&
hasher()
key_equal const&
key_equal()
allocator_type const&
allocator_type()
size
() == 0

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.

If the defaults are used, `hasher`, `key_equal` and `allocator_type` need to be `DefaultConstructible`.

InputIterator
InputIterator
size_type
implementation-defined
hasher const&
hasher()
key_equal const&
key_equal()
allocator_type const&
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.

If the defaults are used, `hasher`, `key_equal` and `allocator_type` need to be `DefaultConstructible`.

unordered_map const&

The copy constructor. Copies the contained elements, hash function, predicate, maximum load factor and allocator.

If `Allocator::select_on_container_copy_construction` exists and has the right signature, the allocator will be constructed from its result.

`value_type` is copy constructible

unordered_map &&

The move constructor.

This is implemented using Boost.Move.

`value_type` is move constructible.

On compilers without rvalue reference support the emulation does not support moving without calling `boost::move` if `value_type` is not copyable. So, for example, you can't return the container from a function.

Allocator const&

Constructs an empty container, using allocator `a`.

unordered_map const&
Allocator const&

Constructs an container, copying `x`'s contained elements, hash function, predicate, maximum load factor, but using allocator `a`.

unordered_map &&
Allocator const&

Construct a container moving `x`'s contained elements, and having the hash function, predicate and maximum load factor, but using allocate `a`.

This is implemented using Boost.Move.

`value_type` is move insertable.

initializer_list<value_type>
size_type
implementation-defined
hasher const&
hasher()
key_equal const&
key_equal()
allocator_type const&
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 `il` into it.

If the defaults are used, `hasher`, `key_equal` and `allocator_type` need to be `DefaultConstructible`.

size_type
allocator_type const&
size
() == 0

Constructs an empty container with at least `n` buckets, using `hf` as the hash function, the default hash function and key equality predicate, `a` as the allocator and a maximum load factor of 1.0.

`hasher` and `key_equal` need to be `DefaultConstructible`.

size_type
hasher const&
allocator_type const&
size
() == 0

Constructs an empty container with at least `n` buckets, using `hf` as the hash function, the default key equality predicate, `a` as the allocator and a maximum load factor of 1.0.

`key_equal` needs to be `DefaultConstructible`.

InputIterator
InputIterator
size_type
allocator_type const&

Constructs an empty container with at least `n` buckets, using `a` as the allocator, with the default hash function and key equality predicate and a maximum load factor of 1.0 and inserts the elements from [f, l) into it.

`hasher`, `key_equal` need to be `DefaultConstructible`.

InputIterator
InputIterator
size_type
hasher const&
allocator_type const&

Constructs an empty container with at least `n` buckets, using `hf` as the hash function, `a` as the allocator, with the default key equality predicate and a maximum load factor of 1.0 and inserts the elements from [f, l) into it.

`key_equal` needs to be `DefaultConstructible`.

The destructor is applied to every element, and all memory is deallocated

unordered_map const&
unordered_map&

The assignment operator. Copies the contained elements, hash function, predicate and maximum load factor but not the allocator.

If `Alloc::propagate_on_container_copy_assignment` exists and `Alloc::propagate_on_container_copy_assignment::value` is true, the allocator is overwritten, if not the copied elements are created using the existing allocator.

`value_type` is copy constructible

unordered_map &&
unordered_map&

The move assignment operator.

If `Alloc::propagate_on_container_move_assignment` exists and `Alloc::propagate_on_container_move_assignment::value` is true, the allocator is overwritten, if not the moved elements are created using the existing allocator.

On compilers without rvalue references, this is emulated using Boost.Move. Note that on some compilers the copy assignment operator may be used in some circumstances.

`value_type` is move constructible.

initializer_list<value_type>
unordered_map&

Assign from values in initializer list. All existing elements are either overwritten by the new elements or destroyed.

`value_type` is `CopyInsertable` into the container and `CopyAssignable`.

allocator_type
bool ``size`() == 0`
size_type `std::distance(`begin`(), `end`())`
size_type ``size`()` of the largest possible container.
iterator
const_iterator
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
const_iterator
An iterator which refers to the past-the-end value for the container.
const_iterator 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 A constant iterator which refers to the past-the-end value for the container.
Args&&
std::pair<iterator, bool>

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 key.

`value_type` is `EmplaceConstructible` into `X` from `args`.

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 key.

If an exception is thrown by an operation other than a call to `hasher` the function has no effect.

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.

If the compiler doesn't support variadic template arguments or rvalue references, this is emulated for up to 10 arguments, with no support for rvalue references or move semantics.

Since existing `std::pair` implementations don't support `std::piecewise_construct` this emulates it, but using `boost::unordered::piecewise_construct`.

const_iterator
Args&&
iterator

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 key.

`hint` is a suggestion to where the element should be inserted.

`value_type` is `EmplaceConstructible` into `X` from `args`.

If an insert took place, then the iterator points to the newly inserted element. Otherwise, it points to the element with equivalent key.

If an exception is thrown by an operation other than a call to `hasher` the function has no effect.

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 key.

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.

If the compiler doesn't support variadic template arguments or rvalue references, this is emulated for up to 10 arguments, with no support for rvalue references or move semantics.

Since existing `std::pair` implementations don't support `std::piecewise_construct` this emulates it, but using `boost::unordered::piecewise_construct`.

value_type const&
std::pair<iterator, bool>

Inserts `obj` in the container if and only if there is no element in the container with an equivalent key.

`value_type` is `CopyInsertable`.

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 key.

If an exception is thrown by an operation other than a call to `hasher` the function has no effect.

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.

value_type&&
std::pair<iterator, bool>

Inserts `obj` in the container if and only if there is no element in the container with an equivalent key.

`value_type` is `MoveInsertable`.

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 key.

If an exception is thrown by an operation other than a call to `hasher` the function has no effect.

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.

const_iterator
value_type const&
iterator

Inserts `obj` in the container if and only if there is no element in the container with an equivalent key.

hint is a suggestion to where the element should be inserted.

`value_type` is `CopyInsertable`.

If an insert took place, then the iterator points to the newly inserted element. Otherwise, it points to the element with equivalent key.

If an exception is thrown by an operation other than a call to `hasher` the function has no effect.

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 key.

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.

const_iterator
value_type&&
iterator

Inserts `obj` in the container if and only if there is no element in the container with an equivalent key.

hint is a suggestion to where the element should be inserted.

`value_type` is `MoveInsertable`.

If an insert took place, then the iterator points to the newly inserted element. Otherwise, it points to the element with equivalent key.

If an exception is thrown by an operation other than a call to `hasher` the function has no effect.

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 key.

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.

InputIterator
InputIterator
void

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 key.

`value_type` is `EmplaceConstructible` into `X` from `*first`.

When inserting a single element, if an exception is thrown by an operation other than a call to `hasher` the function has no effect.

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.

initializer_list<value_type>
void

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 key.

`value_type` is `EmplaceConstructible` into `X` from `*first`.

When inserting a single element, if an exception is thrown by an operation other than a call to `hasher` the function has no effect.

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.

initializer_list<value_type>
void

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 key.

`value_type` is `EmplaceConstructible` into `X` from `*first`.

When inserting a single element, if an exception is thrown by an operation other than a call to `hasher` the function has no effect.

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.

const_iterator
node_type

Removes the element pointed to by `position`.

A `node_type` owning the element.

In C++17 a node extracted using this method can be inserted into a compatible `unordered_multimap`, but that is not supported yet.

key_type const&
node_type

Removes an element with key equivalent to `k`.

A `node_type` owning the element if found, otherwise an empty `node_type`.

Only throws an exception if it is thrown by `hasher` or `key_equal`.

In C++17 a node extracted using this method can be inserted into a compatible `unordered_multimap`, but that is not supported yet.

node_type&&
insert_return_type

If `nh` is empty, has no affect.

Otherwise inserts the element owned by `nh` if and only if there is no element in the container with an equivalent key.

`nh` is empty or `nh.get_allocator()` is equal to the container's allocator.

If `nh` was empty, returns an `insert_return_type` with: `inserted` equal to `false`, `position` equal to `end()` and `node` empty.

Otherwise if there was already an element with an equivalent key, returns an `insert_return_type` with: `inserted` equal to `false`, `position` pointing to a matching element and `node` contains the node from `nh`.

Otherwise if the insertion succeeded, returns an `insert_return_type` with: `inserted` equal to `true`, `position` pointing to the newly inserted element and `node` empty.

If an exception is thrown by an operation other than a call to `hasher` the function has no effect.

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.

In C++17 this can be used to insert a node extracted from a compatible `unordered_multimap`, but that is not supported yet.

const_iterator
node_type&&
iterator

If `nh` is empty, has no affect.

Otherwise inserts the element owned by `nh` if and only if there is no element in the container with an equivalent key.

If there is already an element in the container with an equivalent key has no effect on `nh` (i.e. `nh` still contains the node.)

hint is a suggestion to where the element should be inserted.

`nh` is empty or `nh.get_allocator()` is equal to the container's allocator.

If `nh` was empty returns `end()`.

If there was already an element in the container with an equivalent key returns an iterator pointing to that.

Otherwise returns an iterator pointing to the newly inserted element.

If an exception is thrown by an operation other than a call to `hasher` the function has no effect.

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 key.

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.

In C++17 this can be used to insert a node extracted from a compatible `unordered_multimap`, but that is not supported yet.

const_iterator
iterator

Erase the element pointed to by `position`.

The iterator following `position` before the erasure.

Only throws an exception if it is thrown by `hasher` or `key_equal`.

In older versions this could be inefficient because it had to search through several buckets to find the position of the returned iterator. The data structure has been changed so that this is no longer the case, and the alternative erase methods have been deprecated.

key_type const&
size_type

Erase all elements with key equivalent to `k`.

The number of elements erased.

Only throws an exception if it is thrown by `hasher` or `key_equal`.

const_iterator
const_iterator
iterator

Erases the elements in the range from `first` to `last`.

The iterator following the erased elements - i.e. `last`.

Only throws an exception if it is thrown by `hasher` or `key_equal`.

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.

const_iterator
void

Erase the element pointed to by `position`.

Only throws an exception if it is thrown by `hasher` or `key_equal`.

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.

This method was implemented because returning an iterator to the next element from `erase` was expensive, but the container has been redesigned so that is no longer the case. So this method is now deprecated.

const_iterator
void

Erase the element pointed to by `position`.

Only throws an exception if it is thrown by `hasher` or `key_equal`.

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.

This method was implemented because returning an iterator to the next element from `erase` was expensive, but the container has been redesigned so that is no longer the case. So this method is now deprecated.

void

Erases all elements in the container.

``size`() == 0`

Never throws an exception.

unordered_map&
void

Swaps the contents of the container with the parameter.

If `Allocator::propagate_on_container_swap` is declared and `Allocator::propagate_on_container_swap::value` is true then the containers' allocators are swapped. Otherwise, swapping with unequal allocators results in undefined behavior.

Doesn't throw an exception unless it is thrown by the copy constructor or copy assignment operator of `key_equal` or `hasher`.

The exception specifications aren't quite the same as the C++11 standard, as the equality predieate and hash function are swapped using their copy constructors.

unordered_map<Key, Mapped, H2, P2, Alloc>&

Does not support merging with a compatible `unordered_multimap` yet.

unordered_map<Key, Mapped, H2, P2, Alloc>&&

Does not support merging with a compatible `unordered_multimap` yet.

hasher The container's hash function.
key_equal The container's key equality predicate.
key_type const&
iterator
key_type const&
const_iterator
CompatibleKey const&
CompatibleHash const&
CompatiblePredicate const&
iterator
CompatibleKey const&
CompatibleHash const&
CompatiblePredicate const&
const_iterator

An iterator pointing to an element with key equivalent to `k`, or `b.end()` if no such element exists.

The templated overloads are a non-standard extensions which allows you to use a compatible hash function and equality predicate for a key of a different type in order to avoid an expensive type cast. In general, its use is not encouraged.

key_type const&
size_type

The number of elements with key equivalent to `k`.

key_type const&
std::pair<iterator, iterator>
key_type const&
std::pair<const_iterator, const_iterator>

A range containing all elements with key equivalent to `k`. If the container doesn't container any such elements, returns `std::make_pair(`b.end`(),`b.end`())`.

key_type const&
mapped_type&

If the container does not already contain an elements with a key equivalent to `k`, inserts the value `std::pair<key_type const, mapped_type>(k, mapped_type())`

A reference to `x.second` where x is the element already in the container, or the newly inserted element with a key equivalent to `k`

If an exception is thrown by an operation other than a call to `hasher` the function has no effect.

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.

Mapped& `key_type const&`
Mapped const& `key_type const&`

A reference to `x.second` where `x` is the (unique) element whose key is equivalent to `k`.

An exception object of type `std::out_of_range` if no such element is present.

size_type

The number of buckets.

size_type

An upper bound on the number of buckets.

size_type
size_type

`n < `bucket_count`()`

The number of elements in bucket `n`.

key_type const&
size_type

The index of the bucket which would contain an element with key `k`.

The return value is less than `bucket_count()`

size_type
local_iterator
size_type
const_local_iterator

`n` shall be in the range `[0, bucket_count())`.

A local iterator pointing the first element in the bucket with index `n`.

size_type
local_iterator
size_type
const_local_iterator

`n` shall be in the range `[0, bucket_count())`.

A local iterator pointing the 'one past the end' element in the bucket with index `n`.

size_type
const_local_iterator

`n` shall be in the range `[0, bucket_count())`.

A constant local iterator pointing the first element in the bucket with index `n`.

size_type
const_local_iterator

`n` shall be in the range `[0, bucket_count())`.

A constant local iterator pointing the 'one past the end' element in the bucket with index `n`.

float

The average number of elements per bucket.

float

Returns the current maximum load factor.

float
void

Changes the container's maximum load factor, using `z` as a hint.

size_type
void

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.

The function has no effect if an exception is thrown, unless it is thrown by the container's hash function or comparison function.

size_type
void

Invalidates iterators, and changes the order of elements. Pointers and references to elements are not invalidated.

The function has no effect if an exception is thrown, unless it is thrown by the container's hash function or comparison function.

unordered_map<Key, Mapped, Hash, Pred, Alloc> const&
unordered_map<Key, Mapped, Hash, Pred, Alloc> const&
bool

Return `true` if `x.size() == y.size` and for every element in `x`, there is an element in `y` with the same for the same key, with an equal value (using `operator==` to compare the value types).

The behavior of this function was changed to match the C++11 standard in Boost 1.48.

Behavior is undefined if the two containers don't have equivalent equality predicates.

unordered_map<Key, Mapped, Hash, Pred, Alloc> const&
unordered_map<Key, Mapped, Hash, Pred, Alloc> const&
bool

Return `false` if `x.size() == y.size` and for every element in `x`, there is an element in `y` with the same for the same key, with an equal value (using `operator==` to compare the value types).

The behavior of this function was changed to match the C++11 standard in Boost 1.48.

Behavior is undefined if the two containers don't have equivalent equality predicates.

unordered_map<Key, Mapped, Hash, Pred, Alloc>&
unordered_map<Key, Mapped, Hash, Pred, Alloc>&
void

`x.swap(y)`

Swaps the contents of `x` and `y`.

If `Allocator::propagate_on_container_swap` is declared and `Allocator::propagate_on_container_swap::value` is true then the containers' allocators are swapped. Otherwise, swapping with unequal allocators results in undefined behavior.

Doesn't throw an exception unless it is thrown by the copy constructor or copy assignment operator of `key_equal` or `hasher`.

The exception specifications aren't quite the same as the C++11 standard, as the equality predieate and hash function are swapped using their copy constructors.

boost::hash<Key>
std::equal_to<Key>
std::allocator<std::pair<Key const, Mapped>>

An unordered associative container that associates keys with another value. The same key can be stored multiple times.

Template Parameters

Key | `Key` must be `Erasable` from the container (i.e. `allocator_traits` can `destroy` it).
Mapped | `Mapped` must be `Erasable` from the container (i.e. `allocator_traits` can `destroy` it).
Hash | A unary function object type that acts a hash function for a `Key`. It takes a single argument of type `Key` and returns a value of type std::size_t.
Pred | A binary function object that implements an equivalence relation on values of type `Key`. 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 and elements with equivalent keys are stored next to each other.

The number of buckets can be automatically increased by a call to insert, or as the result of calling rehash.

Key
std::pair<Key const, Mapped>
Mapped
Hash
Pred
Alloc
typename allocator_type::pointer

`value_type*` if `allocator_type::pointer` is not defined.

typename allocator_type::const_pointer

`boost::pointer_to_other<pointer, value_type>::type` if `allocator_type::const_pointer` is not defined.

value_type&

lvalue of value_type.

value_type const&

const lvalue of value_type.

implementation-defined

An unsigned integral type.

size_type can represent any non-negative value of difference_type.

implementation-defined

A signed integral type.

Is identical to the difference type of iterator and const_iterator.

implementation-defined

An iterator whose value type is value_type.

The iterator category is at least a forward iterator.

Convertible to const_iterator.

implementation-defined

A constant iterator whose value type is value_type.

The iterator category is at least a forward iterator.

implementation-defined

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.

implementation-defined

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.

implementation-defined

See `node_handle_map` for details.

size
() == 0

Constructs an empty container using hasher() as the hash function, key_equal() as the key equality predicate, allocator_type() as the allocator and a maximum load factor of 1.0.

If the defaults are used, `hasher`, `key_equal` and `allocator_type` need to be `DefaultConstructible`.

size_type
hasher const&
hasher()
key_equal const&
key_equal()
allocator_type const&
allocator_type()
size
() == 0

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.

If the defaults are used, `hasher`, `key_equal` and `allocator_type` need to be `DefaultConstructible`.

InputIterator
InputIterator
size_type
implementation-defined
hasher const&
hasher()
key_equal const&
key_equal()
allocator_type const&
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.

If the defaults are used, `hasher`, `key_equal` and `allocator_type` need to be `DefaultConstructible`.

unordered_multimap const&

The copy constructor. Copies the contained elements, hash function, predicate, maximum load factor and allocator.

If `Allocator::select_on_container_copy_construction` exists and has the right signature, the allocator will be constructed from its result.

`value_type` is copy constructible

unordered_multimap &&

The move constructor.

This is implemented using Boost.Move.

`value_type` is move constructible.

On compilers without rvalue reference support the emulation does not support moving without calling `boost::move` if `value_type` is not copyable. So, for example, you can't return the container from a function.

Allocator const&

Constructs an empty container, using allocator `a`.

unordered_multimap const&
Allocator const&

Constructs an container, copying `x`'s contained elements, hash function, predicate, maximum load factor, but using allocator `a`.

unordered_multimap &&
Allocator const&

Construct a container moving `x`'s contained elements, and having the hash function, predicate and maximum load factor, but using allocate `a`.

This is implemented using Boost.Move.

`value_type` is move insertable.

initializer_list<value_type>
size_type
implementation-defined
hasher const&
hasher()
key_equal const&
key_equal()
allocator_type const&
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 `il` into it.

If the defaults are used, `hasher`, `key_equal` and `allocator_type` need to be `DefaultConstructible`.

size_type
allocator_type const&
size
() == 0

Constructs an empty container with at least `n` buckets, using `hf` as the hash function, the default hash function and key equality predicate, `a` as the allocator and a maximum load factor of 1.0.

`hasher` and `key_equal` need to be `DefaultConstructible`.

size_type
hasher const&
allocator_type const&
size
() == 0

Constructs an empty container with at least `n` buckets, using `hf` as the hash function, the default key equality predicate, `a` as the allocator and a maximum load factor of 1.0.

`key_equal` needs to be `DefaultConstructible`.

InputIterator
InputIterator
size_type
allocator_type const&

Constructs an empty container with at least `n` buckets, using `a` as the allocator, with the default hash function and key equality predicate and a maximum load factor of 1.0 and inserts the elements from [f, l) into it.

`hasher`, `key_equal` need to be `DefaultConstructible`.

InputIterator
InputIterator
size_type
hasher const&
allocator_type const&

Constructs an empty container with at least `n` buckets, using `hf` as the hash function, `a` as the allocator, with the default key equality predicate and a maximum load factor of 1.0 and inserts the elements from [f, l) into it.

`key_equal` needs to be `DefaultConstructible`.

The destructor is applied to every element, and all memory is deallocated

unordered_multimap const&
unordered_multimap&

The assignment operator. Copies the contained elements, hash function, predicate and maximum load factor but not the allocator.

If `Alloc::propagate_on_container_copy_assignment` exists and `Alloc::propagate_on_container_copy_assignment::value` is true, the allocator is overwritten, if not the copied elements are created using the existing allocator.

`value_type` is copy constructible

unordered_multimap &&
unordered_multimap&

The move assignment operator.

If `Alloc::propagate_on_container_move_assignment` exists and `Alloc::propagate_on_container_move_assignment::value` is true, the allocator is overwritten, if not the moved elements are created using the existing allocator.

On compilers without rvalue references, this is emulated using Boost.Move. Note that on some compilers the copy assignment operator may be used in some circumstances.

`value_type` is move constructible.

initializer_list<value_type>
unordered_multimap&

Assign from values in initializer list. All existing elements are either overwritten by the new elements or destroyed.

`value_type` is `CopyInsertable` into the container and `CopyAssignable`.

allocator_type
bool ``size`() == 0`
size_type `std::distance(`begin`(), `end`())`
size_type ``size`()` of the largest possible container.
iterator
const_iterator
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
const_iterator
An iterator which refers to the past-the-end value for the container.
const_iterator 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 A constant iterator which refers to the past-the-end value for the container.
Args&&
iterator

Inserts an object, constructed with the arguments `args`, in the container.

`value_type` is `EmplaceConstructible` into `X` from `args`.

An iterator pointing to the inserted element.

If an exception is thrown by an operation other than a call to `hasher` the function has no effect.

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.

If the compiler doesn't support variadic template arguments or rvalue references, this is emulated for up to 10 arguments, with no support for rvalue references or move semantics.

Since existing `std::pair` implementations don't support `std::piecewise_construct` this emulates it, but using `boost::unordered::piecewise_construct`.

const_iterator
Args&&
iterator

Inserts an object, constructed with the arguments `args`, in the container.

`hint` is a suggestion to where the element should be inserted.

`value_type` is `EmplaceConstructible` into `X` from `args`.

An iterator pointing to the inserted element.

If an exception is thrown by an operation other than a call to `hasher` the function has no effect.

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 key.

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.

If the compiler doesn't support variadic template arguments or rvalue references, this is emulated for up to 10 arguments, with no support for rvalue references or move semantics.

Since existing `std::pair` implementations don't support `std::piecewise_construct` this emulates it, but using `boost::unordered::piecewise_construct`.

value_type const&
iterator

Inserts `obj` in the container.

`value_type` is `CopyInsertable`.

An iterator pointing to the inserted element.

If an exception is thrown by an operation other than a call to `hasher` the function has no effect.

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.

value_type&&
iterator

Inserts `obj` in the container.

`value_type` is `MoveInsertable`.

An iterator pointing to the inserted element.

If an exception is thrown by an operation other than a call to `hasher` the function has no effect.

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.

const_iterator
value_type const&
iterator

Inserts `obj` in the container.

hint is a suggestion to where the element should be inserted.

`value_type` is `CopyInsertable`.

An iterator pointing to the inserted element.

If an exception is thrown by an operation other than a call to `hasher` the function has no effect.

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 key.

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.

const_iterator
value_type&&
iterator

Inserts `obj` in the container.

hint is a suggestion to where the element should be inserted.

`value_type` is `MoveInsertable`.

An iterator pointing to the inserted element.

If an exception is thrown by an operation other than a call to `hasher` the function has no effect.

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 key.

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.

InputIterator
InputIterator
void

Inserts a range of elements into the container.

`value_type` is `EmplaceConstructible` into `X` from `*first`.

When inserting a single element, if an exception is thrown by an operation other than a call to `hasher` the function has no effect.

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.

initializer_list<value_type>
void

Inserts a range of elements into the container.

`value_type` is `EmplaceConstructible` into `X` from `*first`.

When inserting a single element, if an exception is thrown by an operation other than a call to `hasher` the function has no effect.

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.

initializer_list<value_type>
void

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 key.

`value_type` is `EmplaceConstructible` into `X` from `*first`.

When inserting a single element, if an exception is thrown by an operation other than a call to `hasher` the function has no effect.

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.

const_iterator
node_type

Removes the element pointed to by `position`.

A `node_type` owning the element.

In C++17 a node extracted using this method can be inserted into a compatible `unordered_map`, but that is not supported yet.

key_type const&
node_type

Removes an element with key equivalent to `k`.

A `node_type` owning the element if found, otherwise an empty `node_type`.

Only throws an exception if it is thrown by `hasher` or `key_equal`.

In C++17 a node extracted using this method can be inserted into a compatible `unordered_map`, but that is not supported yet.

node_type&&
iterator

If `nh` is empty, has no affect.

Otherwise inserts the element owned by `nh`

`nh` is empty or `nh.get_allocator()` is equal to the container's allocator.

If `nh` was empty, returns `end()`.

Otherwise returns an iterator pointing to the newly inserted element.

If an exception is thrown by an operation other than a call to `hasher` the function has no effect.

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.

In C++17 this can be used to insert a node extracted from a compatible `unordered_map`, but that is not supported yet.

const_iterator
node_type&&
iterator

If `nh` is empty, has no affect.

Otherwise inserts the element owned by `nh`

hint is a suggestion to where the element should be inserted.

`nh` is empty or `nh.get_allocator()` is equal to the container's allocator.

If `nh` was empty, returns `end()`.

Otherwise returns an iterator pointing to the newly inserted element.

If an exception is thrown by an operation other than a call to `hasher` the function has no effect.

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 key.

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.

In C++17 this can be used to insert a node extracted from a compatible `unordered_map`, but that is not supported yet.

const_iterator
iterator

Erase the element pointed to by `position`.

The iterator following `position` before the erasure.

Only throws an exception if it is thrown by `hasher` or `key_equal`.

In older versions this could be inefficient because it had to search through several buckets to find the position of the returned iterator. The data structure has been changed so that this is no longer the case, and the alternative erase methods have been deprecated.

key_type const&
size_type

Erase all elements with key equivalent to `k`.

The number of elements erased.

Only throws an exception if it is thrown by `hasher` or `key_equal`.

const_iterator
const_iterator
iterator

Erases the elements in the range from `first` to `last`.

The iterator following the erased elements - i.e. `last`.

Only throws an exception if it is thrown by `hasher` or `key_equal`.

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.

const_iterator
void

Erase the element pointed to by `position`.

Only throws an exception if it is thrown by `hasher` or `key_equal`.

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.

This method was implemented because returning an iterator to the next element from `erase` was expensive, but the container has been redesigned so that is no longer the case. So this method is now deprecated.

const_iterator
void

Erase the element pointed to by `position`.

Only throws an exception if it is thrown by `hasher` or `key_equal`.

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.

This method was implemented because returning an iterator to the next element from `erase` was expensive, but the container has been redesigned so that is no longer the case. So this method is now deprecated.

void

Erases all elements in the container.

``size`() == 0`

Never throws an exception.

unordered_multimap&
void

Swaps the contents of the container with the parameter.

If `Allocator::propagate_on_container_swap` is declared and `Allocator::propagate_on_container_swap::value` is true then the containers' allocators are swapped. Otherwise, swapping with unequal allocators results in undefined behavior.

Doesn't throw an exception unless it is thrown by the copy constructor or copy assignment operator of `key_equal` or `hasher`.

The exception specifications aren't quite the same as the C++11 standard, as the equality predieate and hash function are swapped using their copy constructors.

unordered_multimap<Key, Mapped, H2, P2, Alloc>&

Does not support merging with a compatible `unordered_map` yet.

unordered_multimap<Key, Mapped, H2, P2, Alloc>&&

Does not support merging with a compatible `unordered_map` yet.

hasher The container's hash function.
key_equal The container's key equality predicate.
key_type const&
iterator
key_type const&
const_iterator
CompatibleKey const&
CompatibleHash const&
CompatiblePredicate const&
iterator
CompatibleKey const&
CompatibleHash const&
CompatiblePredicate const&
const_iterator

An iterator pointing to an element with key equivalent to `k`, or `b.end()` if no such element exists.

The templated overloads are a non-standard extensions which allows you to use a compatible hash function and equality predicate for a key of a different type in order to avoid an expensive type cast. In general, its use is not encouraged.

key_type const&
size_type

The number of elements with key equivalent to `k`.

key_type const&
std::pair<iterator, iterator>
key_type const&
std::pair<const_iterator, const_iterator>

A range containing all elements with key equivalent to `k`. If the container doesn't container any such elements, returns `std::make_pair(`b.end`(),`b.end`())`.

size_type

The number of buckets.

size_type

An upper bound on the number of buckets.

size_type
size_type

`n < `bucket_count`()`

The number of elements in bucket `n`.

key_type const&
size_type

The index of the bucket which would contain an element with key `k`.

The return value is less than `bucket_count()`

size_type
local_iterator
size_type
const_local_iterator

`n` shall be in the range `[0, bucket_count())`.

A local iterator pointing the first element in the bucket with index `n`.

size_type
local_iterator
size_type
const_local_iterator

`n` shall be in the range `[0, bucket_count())`.

A local iterator pointing the 'one past the end' element in the bucket with index `n`.

size_type
const_local_iterator

`n` shall be in the range `[0, bucket_count())`.

A constant local iterator pointing the first element in the bucket with index `n`.

size_type
const_local_iterator

`n` shall be in the range `[0, bucket_count())`.

A constant local iterator pointing the 'one past the end' element in the bucket with index `n`.

float

The average number of elements per bucket.

float

Returns the current maximum load factor.

float
void

Changes the container's maximum load factor, using `z` as a hint.

size_type
void

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.

The function has no effect if an exception is thrown, unless it is thrown by the container's hash function or comparison function.

size_type
void

Invalidates iterators, and changes the order of elements. Pointers and references to elements are not invalidated.

The function has no effect if an exception is thrown, unless it is thrown by the container's hash function or comparison function.

unordered_multimap<Key, Mapped, Hash, Pred, Alloc> const&
unordered_multimap<Key, Mapped, Hash, Pred, Alloc> const&
bool

Return `true` if `x.size() == y.size` and for every equivalent key group in `x`, there is a group in `y` for the same key, which is a permutation (using `operator==` to compare the value types).

The behavior of this function was changed to match the C++11 standard in Boost 1.48.

Behavior is undefined if the two containers don't have equivalent equality predicates.

unordered_multimap<Key, Mapped, Hash, Pred, Alloc> const&
unordered_multimap<Key, Mapped, Hash, Pred, Alloc> const&
bool

Return `false` if `x.size() == y.size` and for every equivalent key group in `x`, there is a group in `y` for the same key, which is a permutation (using `operator==` to compare the value types).

The behavior of this function was changed to match the C++11 standard in Boost 1.48.

Behavior is undefined if the two containers don't have equivalent equality predicates.

unordered_multimap<Key, Mapped, Hash, Pred, Alloc>&
unordered_multimap<Key, Mapped, Hash, Pred, Alloc>&
void

`x.swap(y)`

Swaps the contents of `x` and `y`.

If `Allocator::propagate_on_container_swap` is declared and `Allocator::propagate_on_container_swap::value` is true then the containers' allocators are swapped. Otherwise, swapping with unequal allocators results in undefined behavior.

Doesn't throw an exception unless it is thrown by the copy constructor or copy assignment operator of `key_equal` or `hasher`.

The exception specifications aren't quite the same as the C++11 standard, as the equality predieate and hash function are swapped using their copy constructors.

An object that owns a single element extracted from an `unordered_map` or an `unordered_multimap`, that can then be inserted into a compatible container type.

The name and template parameters of this type are implementation defined, and should be obtained using the `node_type` member typedef from the appropriate container.

typename Container::key_type
typename Container::mapped_type
typename Container::allocator_type>
node_handle_map &&
node_handle_map&&
node_handle_map&
key_type&
mapped_type&
allocator_type
bool
node_handle_map&
void

In C++17 is also `noexcept` if `ator_traits::is_always_equal::value` is true. But we don't support that trait yet.

node_handle_map<ImplementationDefined>&
node_handle_map<ImplementationDefined>&
void

`x.swap(y)`