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# operator==,!=(std::unordered_multimap)

From cppreference.com
< cpp‎ | container‎ | unordered multimap

[edit template]

template< class Key, class T, class Hash, class KeyEqual, class Allocator > bool operator==( const unordered_multimap<Key,T,Hash,KeyEqual,Allocator>& lhs, const unordered_multimap<Key,T,Hash,KeyEqual,Allocator>& rhs ); | (1) |
template< class Key, class T, class Hash, class KeyEqual, class Allocator > bool operator!=( const unordered_multimap<Key,T,Hash,KeyEqual,Allocator>& lhs, const unordered_multimap<Key,T,Hash,KeyEqual,Allocator>& rhs ); | (2) |

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 and KeyEqual do not have the same behavior on lhs and rhs or if operator== for `value_type` is not a refinement of the partition into equivalent-key groups introduced by KeyEqual (that is, if two elements that compare equal using operator== fall into different partitions)

### [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 ΣSi2 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, where S is the size of the ith equivalent key group. Proprotional to N2 in the worst case, where N is the size of the container. Average case becomes proportional to N if the elements within each equivalent key group are arranged in the same order (happens when the containers are copies of each other).

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