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

From cppreference.com
< cpp‎ | memory‎ | shared ptr
 
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Defined in header <memory>
Compare two shared_ptr objects.
template< class T, class U >

bool operator==( const std::shared_ptr<T>& lhs,

                 const std::shared_ptr<U>& rhs ) noexcept;
 (1) (since C++11)
template< class T, class U >

bool operator!=( const std::shared_ptr<T>& lhs,

                 const std::shared_ptr<U>& rhs ) noexcept;
 (2) (since C++11)
(until C++20)
template< class T, class U >

bool operator<( const std::shared_ptr<T>& lhs,

                const std::shared_ptr<U>& rhs ) noexcept;
 (3) (since C++11)
(until C++20)
template< class T, class U >

bool operator>( const std::shared_ptr<T>& lhs,

                const std::shared_ptr<U>& rhs ) noexcept;
 (4) (since C++11)
(until C++20)
template< class T, class U >

bool operator<=( const std::shared_ptr<T>& lhs,

                 const std::shared_ptr<U>& rhs ) noexcept;
 (5) (since C++11)
(until C++20)
template< class T, class U >

bool operator>=( const std::shared_ptr<T>& lhs,

                 const std::shared_ptr<U>& rhs ) noexcept;
 (6) (since C++11)
(until C++20)
template< class T, class U >

std::strong_ordering operator<=>( const std::shared_ptr<T>& lhs,

                                  const std::shared_ptr<U>& rhs ) noexcept;
 (7) (since C++20)
Compare a shared_ptr with a null pointer.
template< class T >
bool operator==( const std::shared_ptr<T>& lhs, std::nullptr_t ) noexcept;
 (8) (since C++11)
template< class T >
bool operator==( std::nullptr_t, const std::shared_ptr<T>& rhs ) noexcept;
 (9) (since C++11)
(until C++20)
template< class T >
bool operator!=( const std::shared_ptr<T>& lhs, std::nullptr_t ) noexcept;
 (10) (since C++11)
(until C++20)
template< class T >
bool operator!=( std::nullptr_t, const std::shared_ptr<T>& rhs ) noexcept;
 (11) (since C++11)
(until C++20)
template< class T >
bool operator<( const std::shared_ptr<T>& lhs, std::nullptr_t ) noexcept;
 (12) (since C++11)
(until C++20)
template< class T >
bool operator<( std::nullptr_t, const std::shared_ptr<T>& rhs ) noexcept;
 (13) (since C++11)
(until C++20)
template< class T >
bool operator>( const std::shared_ptr<T>& lhs, std::nullptr_t ) noexcept;
 (14) (since C++11)
(until C++20)
template< class T >
bool operator>( std::nullptr_t, const std::shared_ptr<T>& rhs ) noexcept;
 (15) (since C++11)
(until C++20)
template< class T >
bool operator<=( const std::shared_ptr<T>& lhs, std::nullptr_t ) noexcept;
 (16) (since C++11)
(until C++20)
template< class T >
bool operator<=( std::nullptr_t, const std::shared_ptr<T>& rhs ) noexcept;
 (17) (since C++11)
(until C++20)
template< class T >
bool operator>=( const std::shared_ptr<T>& lhs, std::nullptr_t ) noexcept;
 (18) (since C++11)
(until C++20)
template< class T >
bool operator>=( std::nullptr_t, const std::shared_ptr<T>& rhs ) noexcept;
 (19) (since C++11)
(until C++20)
template< class T >

std::strong_ordering operator<=>( const std::shared_ptr<T>& lhs,

                                  std::nullptr_t ) noexcept;
 (20) (since C++20)

Compares two shared_ptr<T> objects or compares shared_ptr<T> with a null pointer.

Note that the comparison operators for shared_ptr simply compare pointer values; the actual objects pointed to are not compared. Having operator< defined for shared_ptr allows shared_ptrs to be used as keys in associative containers, like std::map and std::set.

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

(since C++20)

Contents

[edit] Parameters

lhs - the left-hand shared_ptr to compare
rhs - the right-hand shared_ptr to compare

[edit] Return value

1) lhs.get() == rhs.get()
2) !(lhs == rhs)
3) std::less<V>()(lhs.get(), rhs.get()), where V is the composite pointer type of std::shared_ptr<T>::element_type* and std::shared_ptr<U>::element_type*.
4) rhs < lhs
5) !(rhs < lhs)
6) !(lhs < rhs)
7) std::compare_three_way{}(x.get(), y.get())
8) !lhs
9) !rhs
10) (bool)lhs
11) (bool)rhs
12) std::less<std::shared_ptr<T>::element_type*>()(lhs.get(), nullptr)
13) std::less<std::shared_ptr<T>::element_type*>()(nullptr, rhs.get())
14) nullptr < lhs
15) rhs < nullptr
16) !(nullptr < lhs)
17) !(rhs < nullptr)
18) !(lhs < nullptr)
19) !(nullptr < rhs)
20) std::compare_three_way{}(x.get(), static_cast<