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Showing content from https://cplusplus.com/reference/unordered_set/unordered_multiset/operators/ below:

function template

<unordered_set>

std::operators (unordered_multiset) equality (1)

template <class Key, class Hash, class Pred, class Alloc>  bool operator== ( const unordered_multiset<Key,Hash,Pred,Alloc>& lhs,                    const unordered_multiset<Key,Hash,Pred,Alloc>& rhs );

inequality (2)

template <class Key, class Hash, class Pred, class Alloc>  bool operator!= ( const unordered_multiset<Key,Hash,Pred,Alloc>& lhs,                    const unordered_multiset<Key,Hash,Pred,Alloc>& rhs );

Relational operators for unordered_multiset

These overloaded global operator functions perform the appropriate equality or inequality comparison operation between the unordered_multiset containers lhs and rhs.

The procedure for the equality comparison is as follows (stopping at any point if the procedure finds a conclusive answer):

First, the sizes are compared (size).
For every group of equivalent values (such as those returned by equal_range):
- sizes are compared (count).
- all possible permutations of each group are compared (permutation).
Note that the unordered_multiset::hash_function and unordered_multiset::key_eq objects are expected to have the same behavior in both lhs and rhs.

Parameters

lhs, rhs: unordered_multiset containers (to the left- and right-hand side of the operator, respectively), having both the same template parameters (Key, Hash, Pred and Alloc).

Return Valuetrue if the condition holds, and false otherwise.

Example

// unordered_multiset comparisons
#include <iostream>
#include <string>
#include <unordered_set>

int main ()
{
  std::unordered_multiset<std::string>
    a = {"AAPL","MSFT","GOOG"},
    b = {"MSFT","GOOG","AAPL"},
    c = {"MSFT","GOOG","AAPL","AAPL"};

  if (a==b) std::cout << "a and b are equal\n";
  if (b!=c) std::cout << "b and c are not equal\n";

  return 0;
}

Output:

a and b are equal
b and c are not equal

Complexity Average case: linear in size.
Worst case: quadratic in size.

Iterator validity No changes.

See also

unordered_set::equal_range: Get range of elements with a specific key (public member function)

unordered_set::operator=: Assign content (public member function)

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