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

 

C++

Compiler support

Freestanding and hosted

Language

Standard library

Standard library headers

Named requirements

Feature test macros (C++20)

Language support library

Concepts library (C++20)

Diagnostics library

Memory management library

Metaprogramming library (C++11)

General utilities library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Strings library

Text processing library

Numerics library

Date and time library

Input/output library

Filesystem library (C++17)

Concurrency support library (C++11)

Execution control library (C++26)

Technical specifications

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::unique_ptr

Member functions

unique_ptr::unique_ptr

unique_ptr::~unique_ptr

unique_ptr::operator=

Modifiers

unique_ptr::release

unique_ptr::reset

unique_ptr::swap

Observers

unique_ptr::get

unique_ptr::get_deleter

unique_ptr::operator bool

unique_ptr::operator*unique_ptr::operator->

unique_ptr::operator[]

Non-member functions

make_uniquemake_unique_for_overwrite (C++14)(C++20)

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

operator<< (C++20)

swap(std::unique_ptr)

Helper classes

hash<std::unique_ptr>

 

Defined in header <memory>
template< class T1, class D1, class T2, class D2 > bool operator==( const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y );	(1)	(since C++11) (constexpr since C++23)
template< class T1, class D1, class T2, class D2 > bool operator!=( const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y );	(2)	(since C++11) (until C++20)
template< class T1, class D1, class T2, class D2 > bool operator<( const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y );	(3)	(since C++11)
template< class T1, class D1, class T2, class D2 > bool operator<=( const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y );	(4)	(since C++11)
template< class T1, class D1, class T2, class D2 > bool operator>( const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y );	(5)	(since C++11)
template< class T1, class D1, class T2, class D2 > bool operator>=( const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y );	(6)	(since C++11)
template< class T1, class D1, class T2, class D2 > requires std::three_way_comparable_with< typename unique_ptr<T1, D1>::pointer, typename unique_ptr<T2, D2>::pointer> std::compare_three_way_result_t<typename unique_ptr<T1, D1>::pointer, typename unique_ptr<T2, D2>::pointer> operator<=>( const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y );	(7)	(since C++20)
template< class T, class D > bool operator==( const unique_ptr<T, D>& x, std::nullptr_t ) noexcept;	(8)	(since C++11) (constexpr since C++23)
template< class T, class D > bool operator==( std::nullptr_t, const unique_ptr<T, D>& x ) noexcept;	(9)	(since C++11) (until C++20)
template< class T, class D > bool operator!=( const unique_ptr<T, D>& x, std::nullptr_t ) noexcept;	(10)	(since C++11) (until C++20)
template< class T, class D > bool operator!=( std::nullptr_t, const unique_ptr<T, D>& x ) noexcept;	(11)	(since C++11) (until C++20)
template< class T, class D > bool operator<( const unique_ptr<T, D>& x, std::nullptr_t );	(12)	(since C++11) (constexpr since C++23)
template< class T, class D > bool operator<( std::nullptr_t, const unique_ptr<T, D>& y );	(13)	(since C++11) (constexpr since C++23)
template< class T, class D > bool operator<=( const unique_ptr<T, D>& x, std::nullptr_t );	(14)	(since C++11) (constexpr since C++23)
template< class T, class D > bool operator<=( std::nullptr_t, const unique_ptr<T, D>& y );	(15)	(since C++11) (constexpr since C++23)
template< class T, class D > bool operator>( const unique_ptr<T, D>& x, std::nullptr_t );	(16)	(since C++11) (constexpr since C++23)
template< class T, class D > bool operator>( std::nullptr_t, const unique_ptr<T, D>& y );	(17)	(since C++11) (constexpr since C++23)
template< class T, class D > bool operator>=( const unique_ptr<T, D>& x, std::nullptr_t );	(18)	(since C++11) (constexpr since C++23)
template< class T, class D > bool operator>=( std::nullptr_t, const unique_ptr<T, D>& y );	(19)	(since C++11) (constexpr since C++23)
template< class T, class D > requires std::three_way_comparable<typename unique_ptr<T, D>::pointer> std::compare_three_way_result_t<typename unique_ptr<T, D>::pointer> operator<=>( const unique_ptr<T, D>& x, std::nullptr_t );	(20)	(since C++20) (constexpr since C++23)

Compares the pointer values of two unique_ptrs, or a unique_ptr and nullptr.

1-7) Compares two unique_ptrs.

8-20) Compares a unique_ptr and nullptr.

The != operator is synthesized from operator==.

(since C++20)

Parameters

x, y

-

unique_ptrs to compare

Return value

1) x.get() == y.get()

2) x.get() != y.get()

3) std::less<CT>()(x.get(), y.get()), where CT is std::common_type<unique_ptr<T1, D1>::pointer, unique_ptr<T2, D2>::pointer>::type.

4) !(y < x)

5) y < x

6) !(x < y)

7) std::compare_three_way{}(x.get(), y.get())

8,9) !x

10,11) (bool)x

12) std::less<unique_ptr<T,D>::pointer>()(x.get(), nullptr)

13) std::less<unique_ptr<T,D>::pointer>()(nullptr, y.get())

14) !(nullptr < x)

15) !(y < nullptr)

16) nullptr < x

17) y < nullptr

18) !(x < nullptr)

19) !(nullptr < y)

20) std::compare_three_way{}(x.get(), static_cast<typename unique_ptr<T, D>::pointer>(nullptr))

Example

Run this code

#include <iostream>
#include <memory>

int main()
{
    std::unique_ptr<int> p1(new int(42));
    std::unique_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 3426	C++20	operator<=>(unique_ptr, nullptr_t) was ill-formed	constraints and definition fixed

See also

get	returns a pointer to the managed object (public member function)