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

 

C++

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Feature test macros (C++20)

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array (C++11)

vector

vector<bool>

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list

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set

multiset

map

multimap

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unordered_set (C++11)

unordered_multiset (C++11)

unordered_map (C++11)

unordered_multimap (C++11)

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stack

queue

priority_queue

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flat_map (C++23)

flat_multimap (C++23)

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span (C++20)

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std::multimap

Member functions

multimap::multimap

multimap::~multimap

multimap::operator=

multimap::get_allocator

Iterators

multimap::beginmultimap::cbegin (C++11)

multimap::endmultimap::cend (C++11)

multimap::rbeginmultimap::crbegin (C++11)

multimap::rendmultimap::crend (C++11)

Capacity

multimap::empty

multimap::size

multimap::max_size

Modifiers

multimap::clear

multimap::insert

multimap::insert_range (C++23)

multimap::emplace (C++11)

multimap::emplace_hint (C++11)

multimap::erase

multimap::swap

multimap::extract (C++17)

multimap::merge (C++17)

Lookup

multimap::count

multimap::find

multimap::contains (C++20)

multimap::equal_range

multimap::lower_bound

multimap::upper_bound

Observers

multimap::key_comp

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

Compares the contents of two multimaps.

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 multimap'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 multimaps 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 multimap's ordering Compare.

Given two const E lvalues lhs and rhs as left hand operand and right hand operand respectively (where E is std::pair<const Key, T>), 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	-	multimaps whose contents to compare
- T, Key must meet the requirements of EqualityComparable in order to use overloads (1,2).
- Key must meet the requirements of LessThanComparable in order to use overloads (3-6). The ordering relation must establish total order.

Return value

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

2) true if the contents of the multimaps 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 multimap.

3-7) Linear in the size of the multimap.

Example

Run this code

#include <cassert>
#include <map>
 
int main()
{
    std::multimap<int, char> a{{1, 'a'}, {2, 'b'}, {3, 'c'}};
    std::multimap<int, char> b{{1, 'a'}, {2, 'b'}, {3, 'c'}};
    std::multimap<int, char> c{{7, 'Z'}, {8, 'Y'}, {9, 'X'}, {10, 'W'}};
 
    assert
    (""
        "Compare equal containers:" and
        (a != b) == false and
        (a == b) == true and
        (a < b) == false and
        (a <= b) == true and
        (a > b) == false and
        (a >= b) == true and
        (a <=> b) != std::weak_ordering::less and
        (a <=> b) != std::weak_ordering::greater and
        (a <=> b) == std::weak_ordering::equivalent and
 
        "Compare non equal containers:" and
        (a != c) == true and
        (a == c) == false and
        (a < c) == true and
        (a <= c) == true and
        (a > c) == false and
        (a >= c) == false and
        (a <=> c) == std::weak_ordering::less and
        (a <=> c) != std::weak_ordering::equivalent and
        (a <=> c) != std::weak_ordering::greater and
    "");
}