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

 

C++

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Feature test macros (C++20)

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Metaprogramming library (C++11)

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Symbols index

External libraries

 

Memory management library

voidify (exposition only*) Allocators allocator allocator_traits (C++11) allocation_result (C++23) scoped_allocator_adaptor (C++11) pmr::polymorphic_allocator (C++17) allocator_arg (C++11) uses_allocator (C++11) uses_allocator_construction_args (C++20) make_obj_using_allocator (C++20) uninitialized_construct_using_allocator (C++20) Uninitialized memory algorithms uninitialized_copy uninitialized_fill uninitialized_move (C++17) uninitialized_copy_n (C++11) uninitialized_fill_n uninitialized_move_n (C++17) construct_at (C++20) uninitialized_default_construct (C++17) uninitialized_value_construct (C++17) destroy (C++17) uninitialized_default_construct_n (C++17) uninitialized_value_construct_n (C++17) destroy_n (C++17) destroy_at (C++17) Constrained uninitialized memory algorithms ranges::uninitialized_copy (C++20) ranges::uninitialized_fill (C++20) ranges::uninitialized_move (C++20) ranges::uninitialized_copy_n (C++20)  ranges::uninitialized_fill_n (C++20) ranges::uninitialized_move_n (C++20) ranges::construct_at (C++20) ranges::uninitialized_default_construct (C++20) ranges::uninitialized_value_construct (C++20) ranges::destroy (C++20) ranges::uninitialized_default_construct_n (C++20)  ranges::uninitialized_value_construct_n (C++20) ranges::destroy_n (C++20) ranges::destroy_at (C++20) Memory resources pmr::memory_resource (C++17) pmr::get_default_resource (C++17) pmr::set_default_resource (C++17) pmr::new_delete_resource (C++17) pmr::pool_options (C++17) pmr::null_memory_resource (C++17) pmr::synchronized_pool_resource (C++17) pmr::unsynchronized_pool_resource (C++17) pmr::monotonic_buffer_resource (C++17) Explicit lifetime management start_lifetime_as (C++23) start_lifetime_as_array (C++23) Types for composite class design indirect (C++26) polymorphic (C++26) Uninitialized storage (until C++20) raw_storage_iterator (until C++20*) get_temporary_buffer (until C++20*) return_temporary_buffer (until C++20*) Garbage collector support (until C++23) declare_reachable (C++11)(until C++23) declare_no_pointers (C++11)(until C++23) pointer_safety (C++11)(until C++23) undeclare_reachable (C++11)(until C++23) undeclare_no_pointers (C++11)(until C++23) get_pointer_safety (C++11)(until C++23)

Low level memory management operator newoperator new[] operator deleteoperator delete[] nothrow_t nothrow new_handler set_new_handler get_new_handler (C++11) bad_alloc bad_array_new_length (C++11) align_val_t (C++17) destroying_delete_t (C++20) launder (C++17) Smart pointers unique_ptr (C++11) shared_ptr (C++11) weak_ptr (C++11) auto_ptr (until C++17*) owner_less (C++11) owner_less<void> (C++17) owner_hash (C++26) owner_equal (C++26) enable_shared_from_this (C++11) bad_weak_ptr (C++11) default_delete (C++11) out_ptr_t (C++23) inout_ptr_t (C++23) Miscellaneous pointer_traits (C++11) to_address (C++20) addressof (C++11) align (C++11) assume_aligned (C++20) is_sufficiently_aligned (C++26) C Library malloc calloc realloc free aligned_alloc (C++17)

 

std::shared_ptr

Member functions

shared_ptr::shared_ptr

shared_ptr::~shared_ptr

shared_ptr::operator=

Modifiers

shared_ptr::reset

shared_ptr::swap

Observers

shared_ptr::get

shared_ptr::operator*shared_ptr::operator->

shared_ptr::operator[] (C++17)

shared_ptr::use_count

shared_ptr::unique (until C++20*)

shared_ptr::operator bool

shared_ptr::owner_before

shared_ptr::owner_hash (C++26)

shared_ptr::owner_equal (C++26)

Non-member functions

swap(std::shared_ptr)

make_sharedmake_shared_for_overwrite (C++20)

allocate_sharedallocate_shared_for_overwrite (C++20)

static_pointer_castdynamic_pointer_castconst_pointer_castreinterpret_pointer_cast (C++17)

get_deleter

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

operator<<

atomic_xxx functions (until C++26*)

Helper classes

atomic<std::shared_ptr> (C++20)

hash<std::shared_ptr>

Deduction guides(C++17)

 

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)

See More

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)

Parameters

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

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<std::shared_ptr<T>::element_type*>(nullptr))

Notes

In all cases, it is the stored pointer (the one returned by get()) that is compared, rather than the managed pointer (the one passed to the deleter when use_count goes to zero). The two pointers may differ in a std::shared_ptr created using the aliasing constructor.

Example

Run this code

#include <iostream>
#include <memory>

int main()
{
    std::shared_ptr<int> p1(new int(42));
    std::shared_ptr<int> p2(new int(42));

    std::cout << std::boolalpha
        << "(p1 == p1)       : " << (p1 == p1) << '\n'
        << "(p1 <=> p1) == 0 : " << ((p1 <=> p1) == 0) << '\n' // Since C++20

    // p1 and p2 point to different memory locations, so p1 != p2
        << "(p1 == p2)       : " << (p1 == p2) << '\n'
        << "(p1 < p2)        : " << (p1 < p2) << '\n'
        << "(p1 <=> p2) < 0  : " << ((p1 <=> p2) < 0) << '\n'   // Since C++20
        << "(p1 <=> p2) == 0 : " << ((p1 <=> p2) == 0) << '\n'; // Since C++20
}

Possible output:

(p1 == p1)       : true
(p1 <=> p1) == 0 : true
(p1 == p2)       : false
(p1 < p2)        : true
(p1 <=> p2) < 0  : true
(p1 <=> p2) == 0 : false

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR	Applied to	Behavior as published	Correct behavior
LWG 3427	C++20	operator<=>(shared_ptr, nullptr_t) was ill-formed	definition fixed

See also

get	returns the stored pointer (public member function)