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

Defined in header <string_view> 
template< class CharT, class Traits >
constexpr bool operator==( std::basic_string_view<CharT,Traits> lhs, 
                           std::basic_string_view<CharT,Traits> rhs ) noexcept;
 (1) (since C++17) 
template< class CharT, class Traits >
constexpr bool operator!=( std::basic_string_view<CharT,Traits> lhs, 
                           std::basic_string_view<CharT,Traits> rhs ) noexcept;
 (2) (since C++17)
(until C++20) 
template< class CharT, class Traits >
constexpr bool operator<( std::basic_string_view<CharT,Traits> lhs, 
                          std::basic_string_view<CharT,Traits> rhs ) noexcept;
 (3) (since C++17)
(until C++20) 
template< class CharT, class Traits >
constexpr bool operator<=( std::basic_string_view<CharT,Traits> lhs, 
                           std::basic_string_view<CharT,Traits> rhs ) noexcept;
 (4) (since C++17)
(until C++20) 
template< class CharT, class Traits >
constexpr bool operator>( std::basic_string_view<CharT,Traits> lhs, 
                          std::basic_string_view<CharT,Traits> rhs ) noexcept;
 (5) (since C++17)
(until C++20) 
template< class CharT, class Traits >
constexpr bool operator>=( std::basic_string_view<CharT,Traits> lhs, 
                           std::basic_string_view<CharT,Traits> rhs ) noexcept;
 (6) (since C++17)
(until C++20) 
template< class CharT, class Traits >
constexpr /*comp-cat*/
    operator<=>( std::basic_string_view<CharT,Traits> lhs, 
                 std::basic_string_view<CharT,Traits> rhs ) noexcept;
 (7) (since C++20)

Compares two views.

All comparisons are done via the compare() member function (which itself is defined in terms of Traits::compare()):

  • Two views are equal if both the size of lhs and rhs are equal and each character in lhs has an equivalent character in rhs at the same position.
  • The ordering comparisons are done lexicographically -- the comparison is performed by a function equivalent to std::lexicographical_compare.

The return type of three-way comparison operators (/*comp-cat*/) is Traits::comparison_category if that qualified-id denotes a type, std::weak_ordering otherwise. If /*comp-cat*/ is not a comparison category type, the program is ill-formed.

The <, <=, >, >=, and != operators are synthesized from operator<=> and operator== respectively.

 (since C++20)

The implementation shall provide sufficient additional constexpr and noexcept overloads of these functions so that a basic_string_view<CharT,Traits> object sv may be compared to another object t with an implicit conversion to basic_string_view<CharT,Traits>, with semantics identical to comparing sv and basic_string_view<CharT,Traits>(t).

Parameters

lhs, rhs - views to compare

Return value

1-6) true if the corresponding comparison holds, false otherwise.
7) static_cast</*comp-cat*/>(lhs.compare(rhs) <=> 0).

Complexity

Linear in the size of the views.

Notes

Sufficient additional overloads can be implemented through non-deduced context in one parameter type.

Three-way comparison result type of std::string_view, std::wstring_view, std::u8string_view, std::u16string_view and std::u32string_view is std::strong_ordering.

 (since C++20)

Example

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 3432 C++20 the return type of operator<=> was not required to be a comparison category type required

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Last Updated 2022-06-02T22:02:33Z