C++ Library - <unordered_set>


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Introduction

It is an associative container that store unique elements in no particular order, and which allow for fast retrieval of individual elements based on their value.

Definition

Below is definition of std::unordered_set

template < class Key,                        
           class Hash = hash<Key>,        
           class Pred = equal_to<Key>,    
           class Alloc = allocator<Key>   
           > class unordered_set;

Parameters

  • Key − It defines the type of element.

  • Hash − It is a unary function object.

  • Pred − It is a binary predicate that takes two arguments of the same type as the elements and returns a bool.

  • Alloc − It defines the type of allowcater.

Member types

Following member types can be used as parameters or return type by member functions.

member type definition notes
key_type It is the first template parameter (Key)
value_type It is the first template parameter (Key) The same as key_type
hasher It is the second template parameter (Hash) defaults to: hash<key_type>
key_equal It is the third template parameter (Pred) defaults to: equal_to<key_type>
allocator_type It is the fourth template parameter (Alloc) defaults to: allocator<value_type>
reference Alloc::reference
const_reference Alloc::const_reference
pointer Alloc::pointer for the default allocator: value_type*
const_pointer Alloc::const_pointer for the default allocator: const value_type*
iterator a forward iterator to const value_type * convertible to const_iterator
const_iterator a forward iterator to const value_type *
local_iterator a forward iterator to const value_type * convertible to const_local_iterator
const_local_iterator a forward iterator to const value_type *
size_type an unsigned integral type usually the same as size_t
difference_type a signed integral type usually the same as ptrdiff_t

Member functions

Below is list of member functions

S.N. Method & Description
1 (constructor)

It constructs unordered_set.

2 (destructor)

It destroys unordered_set.

3 operator=

It is used to assign the content.

Capacity

S.N. Capacity & Description
1 empty

It is used to test whether container is empty.

2 size

It returns container size.

3 max_size

It returns maximum size.

Iterators

S.N. Iterators & Description
1 begin

It returns iterator to beginning.

2 end

It returns iterator to end.

3 cbegin

It returns const_iterator to beginning.

4 cend

It return const_iterator to end.

Element lookup

S.N. Element lookup & Description
1 find

It is used to get iterator to element.

2 count

It is used to count elements with a specific key.

3 equal_range

It is used to get range of elements with a specific key.

Modifiers

S.N. Modifiers & Description
1 emplace

It is used to construct and insert element.

2 emplace_hint

It is used to construct and insert element with hint.

3 insert

It is used to insert elements.

4 erase

It is used to erase elements.

5 clear

It is used to clear content.

6 swap

It is used to swap content.

Buckets

S.N. Buckets & Description
1 bucket_count

It returns number of buckets.

2 max_bucket_count

It returns maximum number of buckets.

3 bucket_size

It returns bucket size.

4 bucket

It locates element's bucket.

Hash policy

S.N. Hash policy & Description
1 load_factor

It returns load factor.

2 max_load_factor

It is used to get or set maximum load factor.

3 rehash

It is used to set number of buckets.

4 reserve

It gives a request to capacity chage of backets

Observers

S.N. Observers & Description
1 hash_function

It is used to get hash function.

2 key_eq

It is used to get key equivalence predicate.

3 get_allocator

It is used to get allocator.

S.N. Non-member function overloads & Description
1 operators (unordered_set)

It is used to get hash function.

2 swap (unordered_set)

It exchanges contents of two unordered_set containers.

Predefined iterators

S.N. Non-member function overloads & Description
1 operators (unordered_set)

It is used to get hash function.

2 swap (unordered_set)

It exchanges contents of two unordered_set containers.



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