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

From cppreference.net
C++
Memory management library
( exposition only* )
Allocators
Uninitialized memory algorithms
Constrained uninitialized memory algorithms
Memory resources
Uninitialized storage (until C++20)
( until C++20* )
( until C++20* )
( until C++20* )

Garbage collector support (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)
(C++11) (until C++23)
std::unique_ptr
定义于头文件 <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) (自 C++11 起)
(自 C++23 起为 constexpr)
template < class T1, class D1, class T2, class D2 >
bool operator ! = ( const unique_ptr < T1, D1 > & x, const unique_ptr < T2, D2 > & y ) ;
(2) (自 C++11 起)
(直至 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) (自 C++11 起)
template < class T1, class D1, class T2, class D2 >
bool operator <= ( const unique_ptr < T1, D1 > & x, const unique_ptr < T2, D2 > & y ) ;
(4) (自 C++11 起)
template < class T1, class D1, class T2, class D2 >
bool operator > ( const unique_ptr < T1, D1 > & x, const unique_ptr < T2, D2 > & y ) ;
(5) (自 C++11 起)
template < class T1, class D1, class T2, class D2 >
bool operator >= ( const unique_ptr < T1, D1 > & x, const unique_ptr < T2, D2 > & y ) ;
(6) (自 C++11 起)
template < class T1, class D1, class T2, class D2 >

要求满足 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 >

运算符 <=> ( const unique_ptr < T1, D1 > & x, const unique_ptr < T2, D2 > & y ) ;
(7) (C++20 起)
template < class T, class D >
bool operator == ( const unique_ptr < T, D > & x, std:: nullptr_t ) noexcept ;
(8) (自 C++11 起)
(自 C++23 起为 constexpr)
template < class T, class D >
bool operator == ( std:: nullptr_t , const unique_ptr < T, D > & x ) noexcept ;
(9) (自 C++11 起)
(直至 C++20)
template < class T, class D >
bool operator ! = ( const unique_ptr < T, D > & x, std:: nullptr_t ) noexcept ;
(10) (自 C++11 起)
(直至 C++20)
template < class T, class D >
bool operator ! = ( std:: nullptr_t , const unique_ptr < T, D > & x ) noexcept ;
(11) (自 C++11 起)
(直至 C++20)
template < class T, class D >
bool operator < ( const unique_ptr < T, D > & x, std:: nullptr_t ) ;
(12) (自 C++11 起)
(自 C++23 起为 constexpr)
template < class T, class D >
bool operator < ( std:: nullptr_t , const unique_ptr < T, D > & y ) ;
(13) (自 C++11 起)
(自 C++23 起为 constexpr)
template < class T, class D >
bool operator <= ( const unique_ptr < T, D > & x, std:: nullptr_t ) ;
(14) (自 C++11 起)
(自 C++23 起为 constexpr)
template < class T, class D >
bool operator <= ( std:: nullptr_t , const unique_ptr < T, D > & y ) ;
(15) (自 C++11 起)
(自 C++23 起为 constexpr)
template < class T, class D >
bool operator > ( const unique_ptr < T, D > & x, std:: nullptr_t ) ;
(16) (自 C++11 起)
(自 C++23 起为 constexpr)
template < class T, class D >
bool operator > ( std:: nullptr_t , const unique_ptr < T, D > & y ) ;
(17) (自 C++11 起)
(自 C++23 起为 constexpr)
template < class T, class D >
bool operator >= ( const unique_ptr < T, D > & x, std:: nullptr_t ) ;
(18) (自 C++11 起)
(自 C++23 起为 constexpr)
template < class T, class D >
bool operator >= ( std:: nullptr_t , const unique_ptr < T, D > & y ) ;
(19) (自 C++11 起)
(自 C++23 起为 constexpr)
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) (C++20 起)
(C++23 起为 constexpr)

比较两个 unique_ptr 的指针值，或比较一个 unique_ptr 与 nullptr 。

1-7) 比较两个 unique_ptr 。
8-20) 比较一个 unique_ptr 与 nullptr 。

!= 运算符由 operator== 合成。

(C++20 起)

目录

参数

x, y - unique_ptr 待比较的智能指针

返回值

1) x. get ( ) == y. get ( )
2) x. get ( ) ! = y. get ( )
3) std:: less < CT > ( ) ( x. get ( ) , y. get ( ) ) ，其中 CT 为 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 ) )

示例

运行此代码 
#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 和 p2 指向不同的内存地址，因此 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
}

可能的输出： 

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

缺陷报告

以下行为变更缺陷报告被追溯应用于先前发布的C++标准。

问题报告 适用标准 已发布行为 正确行为
LWG 3426 C++20 operator<=>(unique_ptr, nullptr_t) 存在格式错误 修复约束条件和定义

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