std::optional<T>::operator bool, std::optional<T>::has_value

 

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Language support Type support (basic types, RTTI) Library feature-test macros(C++20) Program utilities Variadic functions initializer_list (C++11) is_constant_evaluated (C++20) is_within_lifetime (C++26) source_location (C++20) Coroutine support(C++20) Contract support(C++26) Three-way comparison three_way_comparablethree_way_comparable_with (C++20)(C++20) strong_ordering (C++20) weak_ordering (C++20) partial_ordering (C++20) common_comparison_category (C++20) compare_three_way_result (C++20) compare_three_way (C++20) strong_order (C++20) weak_order (C++20) partial_order (C++20) compare_strong_order_fallback (C++20) compare_weak_order_fallback (C++20) compare_partial_order_fallback (C++20)   is_eqis_ltis_lteq (C++20)(C++20)(C++20)   is_neqis_gtis_gteq (C++20)(C++20)(C++20)

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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

Iterators

optional::begin (C++26)

optional::end (C++26)

Monadic operations

optional::and_then (C++23)

optional::transform (C++23)

optional::or_else (C++23)

Modifiers

optional::emplace

optional::swap

optional::reset

Non-member functions

operator==operator!=operator<operator<=operator>operator>=operator<=> (C++20)

make_optional

swap(std::optional)

Deduction guides

Helper classes

hash<std::optional>

nullopt_t

in_place_t

bad_optional_access

Helper objects

nullopt

in_place

 

constexprexplicit operator bool()constnoexcept;		(since C++17)
constexprbool has_value()constnoexcept;		(since C++17)

Checks whether *this contains a value.

Parameters

(none)

Return value

true if *this contains a value, false if *this does not contain a value.

Example

Run this code

#include <optional>#include <iostream>   int main(){std::cout<<std::boolalpha;   std::optional<int> opt;std::cout<< opt.has_value()<<'\n';   opt =43;if(opt)std::cout<<"value set to "<< opt.value()<<'\n';elsestd::cout<<"value not set\n";   opt.reset();if(opt.has_value())std::cout<<"value still set to "<< opt.value()<<'\n';elsestd::cout<<"value no longer set\n";}

Output:

false value set to 43 value no longer set