operator==,!=,<,<=,>,>=,<=>(std::multiset)

 

C++

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Standard library headers

Named requirements

Feature test macros (C++20)

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Concepts library (C++20)

Metaprogramming library (C++11)

Diagnostics library

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Containers library

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Ranges library (C++20)

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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::multiset

Member functions

multiset::multiset

multiset::~multiset

multiset::operator=

multiset::get_allocator

Iterators

multiset::beginmultiset::cbegin (C++11)

multiset::endmultiset::cend (C++11)

multiset::rbeginmultiset::crbegin (C++11)

multiset::rendmultiset::crend (C++11)

Capacity

multiset::empty

multiset::size

multiset::max_size

Modifiers

multiset::clear

multiset::insert

multiset::emplace (C++11)

multiset::emplace_hint (C++11)

multiset::erase

multiset::swap

multiset::extract (C++17)

multiset::merge (C++17)

Lookup

multiset::count

multiset::find

multiset::contains (C++20)

multiset::equal_range

multiset::lower_bound

multiset::upper_bound

Observers

multiset::key_comp

multiset::value_comp

Non-member functions

std::swap

erase_if (C++20)

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

Deduction guides(C++17)

 

Defined in header <set>
template< class Key, class Compare, class Alloc > bool operator==( const std::multiset<Key,Compare,Alloc>& lhs,                  const std::multiset<Key,Compare,Alloc>& rhs );	(1)
template< class Key, class Compare, class Alloc > bool operator!=( const std::multiset<Key,Compare,Alloc>& lhs,                  const std::multiset<Key,Compare,Alloc>& rhs );	(2)	(until C++20)
template< class Key, class Compare, class Alloc > bool operator<( const std::multiset<Key,Compare,Alloc>& lhs,                 const std::multiset<Key,Compare,Alloc>& rhs );	(3)	(until C++20)
template< class Key, class Compare, class Alloc > bool operator<=( const std::multiset<Key,Compare,Alloc>& lhs,                  const std::multiset<Key,Compare,Alloc>& rhs );	(4)	(until C++20)
template< class Key, class Compare, class Alloc > bool operator>( const std::multiset<Key,Compare,Alloc>& lhs,                 const std::multiset<Key,Compare,Alloc>& rhs );	(5)	(until C++20)
template< class Key, class Compare, class Alloc > bool operator>=( const std::multiset<Key,Compare,Alloc>& lhs,                  const std::multiset<Key,Compare,Alloc>& rhs );	(6)	(until C++20)
template< class Key, class Compare, class Alloc > /* see below */ operator<=>( const std::multiset<Key,Compare,Alloc>& lhs,                              const std::multiset<Key,Compare,Alloc>& rhs );	(7)	(since C++20)

Compares the contents of two multisets.

1-2) Checks if the contents of lhs and rhs are equal, that is, they have the same number of elements and each element in lhs compares equal with the element in rhs at the same position.

3-6) Compares the contents of lhs and rhs lexicographically. The comparison is performed by a function equivalent to std::lexicographical_compare. This comparison ignores the multiset's ordering Compare.

7) Compares the contents of lhs and rhs lexicographically. The comparison is performed as if by calling std::lexicographical_compare_three_way on two multisets with a function object performing synthesized three-way comparison (see below). The return type is same as the result type of synthesized three-way comparison. This comparison ignores the multiset's ordering Compare.

Given two const E lvalues lhs and rhs as left hand operand and right hand operand respectively (where E is Key), synthesized three-way comparison is defined as:

• if std::three_way_comparable_with<E, E> is satisfied, equivalent to lhs <=> rhs;
• otherwise, if comparing two const E lvalues by operator< is well-formed and the result type satisfies boolean-testable, equivalent to

lhs < rhs ? std::weak_ordering::less :
rhs < lhs ? std::weak_ordering::greater :
            std::weak_ordering::equivalent

• otherwise, synthesized three-way comparison is not defined, and operator<=> does not participate in overload resolution.

The behavior of operator<=> is undefined if three_way_comparable_with or boolean-testable is satisfied but not modeled, or operator< is used but E and < do not establish a total order.

The <, <=, >, >=, and != operators are synthesized from operator<=> and operator== respectively.

(since C++20)

Parameters

lhs, rhs	-	multisets whose contents to compare
- Key must meet the requirements of EqualityComparable in order to use overloads (1-2).

Return value

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

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

3) true if the contents of the lhs are lexicographically less than the contents of rhs, false otherwise

4) true if the contents of the lhs are lexicographically less than or equal to the contents of rhs, false otherwise

5) true if the contents of the lhs are lexicographically greater than the contents of rhs, false otherwise

6) true if the contents of the lhs are lexicographically greater than or equal to the contents of rhs, false otherwise

7) The relative order of the first pair of non-equivalent elements in lhs and rhs if there are such elements, lhs.size() <=> rhs.size() otherwise.

Complexity

1-2) Constant if lhs and rhs are of different size, otherwise linear in the size of the multiset

3-7) Linear in the size of the multiset

Example

Run this code

#include <iostream>
#include <set>
 
int main()
{
    std::multiset<int> alice{1, 2, 3};
    std::multiset<int> bob{7, 8, 9, 10};
    std::multiset<int> eve{1, 2, 3};
 
    std::cout << std::boolalpha;
 
    // Compare non equal containers
    std::cout << "alice == bob returns " << (alice == bob) << '\n';
    std::cout << "alice != bob returns " << (alice != bob) << '\n';
    std::cout << "alice <  bob returns " << (alice < bob) << '\n';
    std::cout << "alice <= bob returns " << (alice <= bob) << '\n';
    std::cout << "alice >  bob returns " << (alice > bob) << '\n';
    std::cout << "alice >= bob returns " << (alice >= bob) << '\n';
 
    std::cout << '\n';
 
    // Compare equal containers
    std::cout << "alice == eve returns " << (alice == eve) << '\n';
    std::cout << "alice != eve returns " << (alice != eve) << '\n';
    std::cout << "alice <  eve returns " << (alice < eve) << '\n';
    std::cout << "alice <= eve returns " << (alice <= eve) << '\n';
    std::cout << "alice >  eve returns " << (alice > eve) << '\n';
    std::cout << "alice >= eve returns " << (alice >= eve) << '\n';
}

Output:

alice == bob returns false
alice != bob returns true
alice <  bob returns true
alice <= bob returns true
alice >  bob returns false
alice >= bob returns false
 
alice == eve returns true
alice != eve returns false
alice <  eve returns false
alice <= eve returns true
alice >  eve returns false
alice >= eve returns true