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

From cppreference.com
 
 
 
 
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_eq1lhs_eq2) obtained from lhs.equal_range(lhs_eq1) has a corresponding group of equivalent elements in the other container [rhs_eq1rhs_eq2) obtained from rhs.equal_range(rhs_eq1), that has the following properties:

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)

[edit] Parameters

lhs, rhs - unordered containers to compare

[edit] 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.

[edit] 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.