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

Since C++20

Header: <string_view>

Compares two views.

# Declarations

template< class CharT, class Traits >
constexpr bool operator==( std::basic_string_view<CharT,Traits> lhs,
std::basic_string_view<CharT,Traits> rhs ) noexcept;

(since C++17) (until C++20)

template< class CharT, class Traits >
constexpr bool operator==(
std::basic_string_view<CharT,Traits> lhs,
std::type_identity_t<std::basic_string_view<CharT,Traits>> rhs ) noexcept;

(since 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;

(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;

(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;

(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;

(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;

(since C++17) (until C++20)

template< class CharT, class Traits >
constexpr /*comp-cat*/ operator<=>(
std::basic_string_view<CharT,Traits> lhs,
std::type_identity_t<std::basic_string_view<CharT,Traits>> rhs ) noexcept;

(since C++20)

# Parameters

lhs, rhs: views to compare

# 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.

std::type_identity_t is used for non-deduced context, which makes arguments that implicitly convertible to the string view type comparable with the string view.

# Example

#include <string_view>
 
int main()
{
    using namespace std::literals;
 
    static_assert(""sv == ""sv);
 
    static_assert(""sv == "", "Selects an additional overload until C++20.");
 
    static_assert("" == ""sv, "Selects an additional overload until C++20."
                              "Uses a rewritten candidate since C++20.");
 
    static_assert(!(""sv != ""sv), "Uses the rewritten candidate since C++20.");
 
    static_assert(!(""sv != ""), "Selects an additional overload until C++20;"
                                 "Uses a rewritten candidate since C++20.");
 
    static_assert(!("" != ""sv), "Selects an additional overload until C++20."
                                 "Uses a rewritten candidate since C++20.");
}

# Defect reports

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
LWG 3950	C++20	redundant additional overloads were still required	overload sets reduced