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

 

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Technical Specifications

 

Utilities library

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initializer_list (C++11)
bitset
hash (C++11)
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Relational operators (deprecated in C++20)
rel_ops::operator!=rel_ops::operator>rel_ops::operator<=rel_ops::operator>=
Comparisons (C++20)
strong_order weak_order partial_order strong_equal weak_equal	strong_ordering weak_ordering partial_ordering strong_equality weak_equality	is_eqis_neqis_ltis_lteqis_gtis_gteq
common_comparison_category
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pair tuple (C++11) apply (C++17) make_from_tuple (C++17)	optional (C++17) any (C++17) variant (C++17)
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swap
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std::optional

Member functions

optional::optional

optional::~optional

optional::operator=

Observers

optional::operator->optional::operator*

optional::operator booloptional::has_value

optional::value

optional::value_or

Modifiers

optional::emplace

optional::swap

optional::reset

Non-member functions

operator==operator!=operator<operator<=operator>operator>=

make_optional

swap

Deduction guides

Helper classes

hash

nullopt_t

in_place_t

bad_optional_access

Helper objects

nullopt

in_place

 

Defined in header <optional>
Compare two optional objects
template< class T, class U > constexpr bool operator==( const optional<T>& lhs, const optional<U>& rhs );	(1)	(since C++17)
template< class T, class U > constexpr bool operator!=( const optional<T>& lhs, const optional<U>& rhs );	(2)	(since C++17)
template< class T, class U > constexpr bool operator<( const optional<T>& lhs, const optional<U>& rhs );	(3)	(since C++17)
template< class T, class U > constexpr bool operator<=( const optional<T>& lhs, const optional<U>& rhs );	(4)	(since C++17)
template< class T, class U > constexpr bool operator>( const optional<T>& lhs, const optional<U>& rhs );	(5)	(since C++17)
template< class T, class U > constexpr bool operator>=( const optional<T>& lhs, const optional<U>& rhs );	(6)	(since C++17)
Compare an optional object with a nullopt
template< class T > constexpr bool operator==( const optional<T>& opt, std::nullopt_t ) noexcept;	(7)	(since C++17)
template< class T > constexpr bool operator==( std::nullopt_t, const optional<T>& opt ) noexcept;	(8)	(since C++17)
template< class T > constexpr bool operator!=( const optional<T>& opt, std::nullopt_t ) noexcept;	(9)	(since C++17)
template< class T > constexpr bool operator!=( std::nullopt_t, const optional<T>& opt ) noexcept;	(10)	(since C++17)
template< class T > constexpr bool operator<( const optional<T>& opt, std::nullopt_t ) noexcept;	(11)	(since C++17)
template< class T > constexpr bool operator<( std::nullopt_t, const optional<T>& opt ) noexcept;	(12)	(since C++17)
template< class T > constexpr bool operator<=( const optional<T>& opt, std::nullopt_t ) noexcept;	(13)	(since C++17)
template< class T > constexpr bool operator<=( std::nullopt_t, const optional<T>& opt) noexcept;	(14)	(since C++17)
template< class T > constexpr bool operator>( const optional<T>& opt, std::nullopt_t ) noexcept;	(15)	(since C++17)
template< class T > constexpr bool operator>( std::nullopt_t, const optional<T>& opt ) noexcept;	(16)	(since C++17)
template< class T > constexpr bool operator>=( const optional<T>& opt, std::nullopt_t ) noexcept;	(17)	(since C++17)
template< class T > constexpr bool operator>=( std::nullopt_t, const optional<T>& opt ) noexcept;	(18)	(since C++17)
Compare an optional object with a T
template< class T, class U > constexpr bool operator==( const optional<T>& opt, const U& value);	(19)	(since C++17)
template< class T, class U > constexpr bool operator==( const T& value, const optional<U>& opt );	(20)	(since C++17)
template< class T, class U > constexpr bool operator!=( const optional<T>& opt, const U& value );	(21)	(since C++17)
template< class T, class U > constexpr bool operator!=( const T& value, const optional<U>& opt );	(22)	(since C++17)
template< class T, class U > constexpr bool operator<( const optional<T>& opt, const U& value );	(23)	(since C++17)
template< class T, class U > constexpr bool operator<( const T& value, const optional<U>& opt );	(24)	(since C++17)
template< class T, class U > constexpr bool operator<=( const optional<T>& opt, const U& value );	(25)	(since C++17)
template< class T, class U > constexpr bool operator<=( const T& value, const optional<U>& opt);	(26)	(since C++17)
template< class T, class U > constexpr bool operator>( const optional<T>& opt, const U& value );	(27)	(since C++17)
template< class T, class U > constexpr bool operator>( const T& value, const optional<U>& opt );	(28)	(since C++17)
template< class T, class U > constexpr bool operator>=( const optional<T>& opt, const U& value );	(29)	(since C++17)
template< class T, class U > constexpr bool operator>=( const T& value, const optional<U>& opt );	(30)	(since C++17)

Performs comparison operations on optional objects.

1-6) Compares two optional objects, lhs and rhs. The contained values are compared (using the corresponding operator of T) only if both lhs and rhs contain values. Otherwise,

• lhs is considered equal to rhs if, and only if, both lhs and rhs do not contain a value.
• lhs is considered less than rhs if, and only if, rhs contains a value and lhs does not.

7-18) Compares opt with a nullopt. Equivalent to (1-6) when comparing to an optional that does not contain a value.

19-30) Compares opt with a value. The values are compared (using the corresponding operator of T) only if opt contains a value. Otherwise, opt is considered less than value. If the corresponding comparison expression between *opt and value is not well-formed, or if its result is not convertible to bool, the behavior is undefined.

Parameters

lhs, rhs, opt	-	an optional object to compare
value	-	value to compare to the contained value

Return value

1) If bool(lhs) != bool(rhs), returns false

Otherwise, if bool(lhs) == false (and so bool(rhs) == false as well), returns true

Otherwise, returns *lhs == *rhs.

2) If bool(lhs) != bool(rhs), returns true

Otherwise, if bool(lhs) == false (and so bool(rhs) == false as well), returns false

Otherwise, returns *lhs != *rhs.

3) If bool(rhs) == false returns false

Otherwise, if bool(lhs) == false, returns true

Otherwise returns *lhs < *rhs

4) If bool(lhs) == false returns true

Otherwise, if bool(rhs) == false, returns false

Otherwise returns *lhs <= *rhs

5) If bool(lhs) == false returns false

Otherwise, if bool(rhs) == false, returns true

Otherwise returns *lhs > *rhs

6) If bool(rhs) == false returns true

Otherwise, if bool(lhs) == false, returns false

Otherwise returns *lhs >= *rhs

7-8) Returns !opt.

9-10) Returns bool(opt).

11) Returns false.

12) Returns bool(opt).

13) Returns !opt.

14) Returns true.

15) Returns bool(opt).

16) Returns false.

17) Returns true.

18) Returns !opt.

19) Returns bool(opt) ? *opt == value : false.

20) Returns bool(opt) ? value == *opt : false.

21) Returns bool(opt) ? *opt != value : true.

22) Returns bool(opt) ? value != *opt : true.

23) Returns bool(opt) ? *opt < value  : true.

24) Returns bool(opt) ? value < *opt  : false.

25) Returns bool(opt) ? *opt <= value : true.

26) Returns bool(opt) ? value <= *opt : false.

27) Returns bool(opt) ? *opt > value  : false.

28) Returns bool(opt) ? value > *opt  : true.

29) Returns bool(opt) ? *opt >= value : false.

30) Returns bool(opt) ? value >= *opt : true.

Exceptions

1-6, 19-30) (none)

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 2945	C++17	order of template parameters inconsistent for compare-with-T cases	made consistent