operator==,!=(std::unordered_map)

 

C++

Compiler support

Freestanding and hosted

Language

Standard library headers

Named requirements

Feature test macros (C++20)

Language support library

Concepts library (C++20)

Metaprogramming library (C++11)

Diagnostics library

General utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library (C++17)

Regular expressions library (C++11)

Concurrency support library (C++11)

Technical specifications

Symbols index

External libraries

 

Containers library

Sequence

array (C++11)

vector

deque

forward_list (C++11)

list

Associative

set

multiset

map

multimap

Unordered associative

unordered_set (C++11)

unordered_multiset (C++11)

unordered_map (C++11)

unordered_multimap (C++11)

Adaptors

stack

queue

priority_queue

Views

span (C++20)

 

std::unordered_map

Member functions

unordered_map::unordered_map

unordered_map::~unordered_map

unordered_map::operator=

unordered_map::get_allocator

Iterators

unordered_map::beginunordered_map::cbegin

unordered_map::endunordered_map::cend

Capacity

unordered_map::empty

unordered_map::size

unordered_map::max_size

Modifiers

unordered_map::clear

unordered_map::insert

unordered_map::insert_or_assign (C++17)

unordered_map::emplace

unordered_map::emplace_hint

unordered_map::try_emplace (C++17)

unordered_map::erase

unordered_map::swap

unordered_map::extract (C++17)

unordered_map::merge (C++17)

Lookup

unordered_map::at

unordered_map::operator[]

unordered_map::count

unordered_map::find

unordered_map::contains (C++20)

unordered_map::equal_range

Bucket interface

unordered_map::begin(size_type)unordered_map::cbegin(size_type)

unordered_map::end(size_type)unordered_map::cend(size_type)

unordered_map::bucket_count

unordered_map::max_bucket_count

unordered_map::bucket_size

unordered_map::bucket

Hash policy

unordered_map::load_factor

unordered_map::max_load_factor

unordered_map::rehash

unordered_map::reserve

Observers

unordered_map::hash_function

unordered_map::key_eq

Non-member functions

operator==operator!= (until C++20)

std::swap

erase_if (C++20)

Deduction guides(C++17)

 

template< class Key, class T, class Hash, class KeyEqual, class Alloc > bool operator==( const std::unordered_map<Key,T,Hash,KeyEqual,Alloc>& lhs,                  const std::unordered_map<Key,T,Hash,KeyEqual,Alloc>& rhs );	(1)
template< class Key, class T, class Hash, class KeyEqual, class Alloc > bool operator!=( const std::unordered_map<Key,T,Hash,KeyEqual,Alloc>& lhs,                  const std::unordered_map<Key,T,Hash,KeyEqual,Alloc>& rhs );	(2)	(until C++20)

Compares the contents of two unordered containers.

The contents of two unordered containers lhs and rhs are equal if the following conditions hold:

• lhs.size() == rhs.size()
• each group of equivalent elements [lhs_eq1, lhs_eq2) obtained from lhs.equal_range(lhs_eq1) has a corresponding group of equivalent elements in the other container [rhs_eq1, rhs_eq2) obtained from rhs.equal_range(rhs_eq1), that has the following properties:

• std::distance(lhs_eq1, lhs_eq2) == std::distance(rhs_eq1, rhs_eq2).
• std::is_permutation(lhs_eq1, lhs_eq2, rhs_eq1) == true.

The behavior is undefined if Key or T are not EqualityComparable.

The behavior is also undefined if hash_function() and key_eq() do (until C++20)key_eq() does (since C++20) not have the same behavior on lhs and rhs or if operator== for Key is not a refinement of the partition into equivalent-key groups introduced by key_eq() (that is, if two elements that compare equal using operator== fall into different partitions)

The != operator is synthesized from operator==.

(since C++20)

Parameters

lhs, rhs

-

unordered containers to compare

Return value

1) true if the contents of the containers are equal, false otherwise

2) true if the contents of the containers are not equal, false otherwise

Complexity

Proportional to N calls to operator== on value_type, calls to the predicate returned by key_eq, and calls to the hasher returned by hash_function, in the average case, proportional to N² in the worst case where N is the size of the container.