std::optional<T>::operator bool, std::optional<T>::has_value
From cppreference.com
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] Parameters
(none)
[edit] Return value
true if *this contains a value, false if *this does not contain a value.
[edit] 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'; 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