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

bool operator==( const std::basic_string<CharT,Traits,Alloc>& lhs,

                 const std::basic_string<CharT,Traits,Alloc>& rhs );
(C++14 前)
template< class CharT, class Traits, class Alloc >

bool operator==( const std::basic_string<CharT,Traits,Alloc>& lhs,

                 const std::basic_string<CharT,Traits,Alloc>& rhs ) noexcept;
(C++14 起)
(C++20 前)
template< class CharT, class Traits, class Alloc >

constexpr bool
    operator==( const std::basic_string<CharT,Traits,Alloc>& lhs,

                const std::basic_string<CharT,Traits,Alloc>& rhs ) noexcept;
(C++20 起) (2)
template< class CharT, class Traits, class Alloc >

bool operator!=( const std::basic_string<CharT,Traits,Alloc>& lhs,

                 const std::basic_string<CharT,Traits,Alloc>& rhs );
(C++14 前)
template< class CharT, class Traits, class Alloc >

bool operator!=( const std::basic_string<CharT,Traits,Alloc>& lhs,

                 const std::basic_string<CharT,Traits,Alloc>& rhs ) noexcept;
(C++14 起)
(C++20 前) (3)
template< class CharT, class Traits, class Alloc >

bool operator<( const std::basic_string<CharT,Traits,Alloc>& lhs,

                const std::basic_string<CharT,Traits,Alloc>& rhs );
(C++14 前)
template< class CharT, class Traits, class Alloc >

bool operator<( const std::basic_string<CharT,Traits,Alloc>& lhs,

                const std::basic_string<CharT,Traits,Alloc>& rhs ) noexcept;
(C++14 起)
(C++20 前) (4)
template< class CharT, class Traits, class Alloc >

bool operator>=( const std::basic_string<CharT,Traits,Alloc>& lhs,

                 const std::basic_string<CharT,Traits,Alloc>& rhs );
(C++14 前)
template< class CharT, class Traits, class Alloc >

bool operator>=( const std::basic_string<CharT,Traits,Alloc>& lhs,

                 const std::basic_string<CharT,Traits,Alloc>& rhs ) noexcept;
(C++14 起)
(C++20 前) (5)
template< class CharT, class Traits, class Alloc >

bool operator>( const std::basic_string<CharT,Traits,Alloc>& lhs,

                const std::basic_string<CharT,Traits,Alloc>& rhs );
(C++14 前)
template< class CharT, class Traits, class Alloc >

bool operator>( const std::basic_string<CharT,Traits,Alloc>& lhs,

                const std::basic_string<CharT,Traits,Alloc>& rhs ) noexcept;
(C++14 起)
(C++20 前) (6)
template< class CharT, class Traits, class Alloc >

bool operator>=( const std::basic_string<CharT,Traits,Alloc>& lhs,

                 const std::basic_string<CharT,Traits,Alloc>& rhs );
(C++14 前)
template< class CharT, class Traits, class Alloc >

bool operator>=( const std::basic_string<CharT,Traits,Alloc>& lhs,

                 const std::basic_string<CharT,Traits,Alloc>& rhs ) noexcept;
(C++14 起)
(C++20 前)
template< class CharT, class Traits, class Alloc >

constexpr /*comp-cat*/
    operator<=>( const std::basic_string<CharT,Traits,Alloc>& lhs,

                 const std::basic_string<CharT,Traits,Alloc>& rhs ) noexcept;
(7) (C++20 起)
比较一个 basic_string 与 T 的空终止数组
(8)
template< class CharT, class Traits, class Alloc >

bool operator==( const std::basic_string<CharT,Traits,Alloc>& lhs,

                 const CharT* rhs );
(C++20 前)
template< class CharT, class Traits, class Alloc >

constexpr bool operator==( const std::basic_string<CharT,Traits,Alloc>& lhs,

                           const CharT* rhs );
(C++20 起)
template< class CharT, class Traits, class Alloc >

bool operator==( const CharT* lhs,

                 const std::basic_string<CharT,Traits,Alloc>& rhs );
(C++20 前) (9)
template< class CharT, class Traits, class Alloc >

bool operator!=( const std::basic_string<CharT,Traits,Alloc>& lhs,

                 const CharT* rhs );
(C++20 前)
template< class CharT, class Traits, class Alloc >

bool operator!=( const CharT* lhs,

                 const std::basic_string<CharT,Traits,Alloc>& rhs );
(C++20 前) (10)
template< class CharT, class Traits, class Alloc >

bool operator<( const std::basic_string<CharT,Traits,Alloc>& lhs,

                const CharT* rhs );
(C++20 前)
template< class CharT, class Traits, class Alloc >

bool operator<( const CharT* lhs,

                const std::basic_string<CharT,Traits,Alloc>& rhs );
(C++20 前) (11)
template< class CharT, class Traits, class Alloc >

bool operator<=( const std::basic_string<CharT,Traits,Alloc>& lhs,

                 const CharT* rhs );
(C++20 前)
template< class CharT, class Traits, class Alloc >

bool operator<=( const CharT* lhs,

                 const std::basic_string<CharT,Traits,Alloc>& rhs );
(C++20 前) (12)
template< class CharT, class Traits, class Alloc >

bool operator>( const std::basic_string<CharT,Traits,Alloc>& lhs,

                const CharT* rhs );
(C++20 前)
template< class CharT, class Traits, class Alloc >

bool operator>( const CharT* lhs,

                const std::basic_string<CharT,Traits,Alloc>& rhs );
(C++20 前) (13)
template< class CharT, class Traits, class Alloc >

bool operator>=( const std::basic_string<CharT,Traits,Alloc>& lhs,

                 const CharT* rhs );
(C++20 前)
template< class CharT, class Traits, class Alloc >

bool operator>=( const CharT* lhs,

                 const std::basic_string<CharT,Traits,Alloc>& rhs );
(C++20 前)
template< class CharT, class Traits, class Alloc >

constexpr /*comp-cat*/
    operator<=>( const std::basic_string<CharT,Traits,Alloc>& lhs,

                 const CharT* rhs );
(14) (C++20 起)

比较 string 与另一 string 或 CharT 的空终止数组的内容。

所有比较通过 compare() 成员函数进行（它自身以 Traits::compare() 定义）：

  • 若 lhs 与 rhs 的大小相等，且 lhs 中的每个字符有在 rhs 中在同一位置的等价字符，则二个字符串相等。
  • 顺序比较按字典序——以等价于 std::lexicographical_compare 或 std::lexicographical_compare_three_way (C++20 起)的函数进行比较。

三路比较运算符的返回类型（ /*comp-cat*/ ）为 Traits::comparison_category ，若它存在，否则为 std::weak_ordering 。

(C++20 起)
1-7) 比较二个 basic_string 对象。
8-14) 比较 basic_string 对象和 CharT 的空终止数组。

参数

lhs, rhs - 要比较内容的字符串

返回值

1-6,8-13) 若对应比较关系成立则为 true ，否则为 false 。
7,14) static_cast</*comp-cat*/>(lhs.compare(rhs) <=> 0) 。

复杂度

与字符串大小成线性。

注解

若至少一个参数拥有类型 std::string 、 std::wstring 、 std::u8string 、 std::u16string 或 std::u32string ，则 operator<=> 的返回类型是 std::strong_ordering 。

(C++20 起)