Difference between revisions of "cpp/utility/optional/operator bool"
From cppreference.com
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#include <optional> | #include <optional> | ||
#include <iostream> | #include <iostream> | ||
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int main() | int main() | ||
{ | { | ||
Revision as of 13:27, 29 June 2020
| constexpr explicit operator bool() const noexcept; |
(since C++17) | |
| constexpr bool has_value() const noexcept; |
(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'; 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
