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

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C++
Utilities library
General utilities
Relational operators (deprecated in C++20)
Dynamic memory management
Uninitialized memory algorithms
Constrained uninitialized memory algorithms
Allocators
Garbage collection support
(C++11) (until C++23)
(C++11) (until C++23)
(C++11) (until C++23)
(C++11) (until C++23)
(C++11) (until C++23)
(C++11) (until C++23)



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_ptr s, or a unique_ptr and nullptr .

1-7) Compares two unique_ptr s.
8-20) Compares a unique_ptr and nullptr .

The != operator is synthesized from operator== .

(since C++20)

Parameters

x, y - unique_ptr s 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

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