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

 

C++

Language

Standard library headers

Concepts

Utilities library

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Iterators library

Numerics library

Input/output library

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Regular expressions library (C++11)

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Thread support library (C++11)

Filesystem library (C++17)

Technical Specifications

 

Utilities library

Type support (basic types, RTTI, type traits)

Dynamic memory management

Error handling

Program utilities

Variadic functions

Date and time

Function objects

initializer_list (C++11)

bitset

hash (C++11)

Relational operators

rel_ops::operator!=rel_ops::operator>rel_ops::operator<=rel_ops::operator>=

Optional and any

optional (C++17)

any (C++17)

Pairs and tuples

pair

tuple (C++11)

apply (C++17)

piecewise_construct_t (C++11)

piecewise_construct (C++11)

integer_sequence (C++14)

Swap, forward and move

swap

exchange (C++14)

forward (C++11)

move (C++11)

move_if_noexcept (C++11)

Type operations

declval (C++11)

as_const (C++17)

 

std::optional

Member functions

optional::optional

optional::~optional

optional::operator=

Observers

optional::operator->optional::operator*

optional::operator bool

optional::value

optional::value_or

Modifiers

optional::emplace

optional::swap

Non-member functions

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

make_optional

swap

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 > constexpr bool operator==( const optional<T>& lhs, const optional<T>& rhs );	(1)	(since C++17)
template< class T > constexpr bool operator!=( const optional<T>& lhs, const optional<T>& rhs );	(2)	(since C++17)
template< class T > constexpr bool operator<( const optional<T>& lhs, const optional<T>& rhs );	(3)	(since C++17)
template< class T > constexpr bool operator<=( const optional<T>& lhs, const optional<T>& rhs );	(4)	(since C++17)
template< class T > constexpr bool operator>( const optional<T>& lhs, const optional<T>& rhs );	(5)	(since C++17)
template< class T > constexpr bool operator>=( const optional<T>& lhs, const optional<T>& 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 );	(7)	(since C++17)
template< class T > constexpr bool operator==( std::nullopt_t, const optional<T>& opt );	(8)	(since C++17)
template< class T > constexpr bool operator!=( const optional<T>& opt, std::nullopt_t );	(9)	(since C++17)
template< class T > constexpr bool operator!=( std::nullopt_t, const optional<T>& opt );	(10)	(since C++17)
template< class T > constexpr bool operator<( const optional<T>& opt, std::nullopt_t );	(11)	(since C++17)
template< class T > constexpr bool operator<( std::nullopt_t, const optional<T>& opt );	(12)	(since C++17)
template< class T > constexpr bool operator<=( const optional<T>& opt, std::nullopt_t );	(13)	(since C++17)
template< class T > constexpr bool operator<=( std::nullopt_t, const optional<T>& opt);	(14)	(since C++17)
template< class T > constexpr bool operator>( const optional<T>& opt, std::nullopt_t );	(15)	(since C++17)
template< class T > constexpr bool operator>( std::nullopt_t, const optional<T>& opt );	(16)	(since C++17)
template< class T > constexpr bool operator>=( const optional<T>& opt, std::nullopt_t );	(17)	(since C++17)
template< class T > constexpr bool operator>=( std::nullopt_t, const optional<T>& opt );	(18)	(since C++17)
Compare an optional object with a T
template< class T > constexpr bool operator==( const optional<T>& opt, const T& value);	(19)	(since C++17)
template< class T > constexpr bool operator==( const T& value, const optional<T>& opt );	(20)	(since C++17)
template< class T > constexpr bool operator!=( const optional<T>& opt, const T& value );	(21)	(since C++17)
template< class T > constexpr bool operator!=( const T& value, const optional<T>& opt );	(22)	(since C++17)
template< class T > constexpr bool operator<( const optional<T>& opt, const T& value );	(23)	(since C++17)
template< class T > constexpr bool operator<( const T& value, const optional<T>& opt );	(24)	(since C++17)
template< class T > constexpr bool operator<=( const optional<T>& opt, const T& value );	(25)	(since C++17)
template< class T > constexpr bool operator<=( const T& value, const optional<T>& opt);	(26)	(since C++17)
template< class T > constexpr bool operator>( const optional<T>& opt, const T& value );	(27)	(since C++17)
template< class T > constexpr bool operator>( const T& value, const optional<T>& opt );	(28)	(since C++17)
template< class T > constexpr bool operator>=( const optional<T>& opt, const T& value );	(39)	(since C++17)
template< class T > constexpr bool operator>=( const T& value, const optional<T>& 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 operator== for (1-2) and operator< for (3-6)) 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 operator== for (19-22) and operator< for (23-30)) only if opt contains a value. Otherwise, opt is considered less than value.

Parameters

lhs, rhs, opt	-	an optional object to compare
value	-	value to compare to the contained value
Type requirements
- T must meet the requirements of EqualityComparable in order to use overloads (1-2).

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) Returns !(lhs == rhs)

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

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

Otherwise returns *x < *y

4) Returns !(rhs < lhs)

5) Returns rhs < lhs

6) 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 !(opt > value).

26) Returns !(value > opt).

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

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

29) Returns !(opt < value).

30) Returns !(value < opt).

Exceptions

1-6) (none)

7-18)

noexcept specification:  

noexcept

  

19-30) (none)