std::optional<T>::operator bool, std::optional<T>::has_value
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Common vocabulary types
std::optional
optional::operator booloptional::has_value
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constexpr explicit operator bool() const noexcept;
(since C++17)
constexpr bool has_value() const noexcept;
(since C++17)
Checks whether *this contains a value.
[edit] Return value
true if *this contains a value, false if *this does not contain a value.
[edit] Example
Run this code
#include <iostream> #include <optional> 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'; else std::cout << "value not set\n"; opt.reset(); if (opt.has_value()) std::cout << "value still set to " << opt.value() << '\n'; else std::cout << "value no longer set\n"; }
Output:
false value set to 43 value no longer set
[edit] See also
checks whether the object contains an expected value
(public member function of
(public member function of
std::expected<T,E>) [edit]