std::optional<T>::value
constexpr T& value() &; constexpr const T& value() const &; |
(1) | (since C++17) |
constexpr T&& value() &&; constexpr const T&& value() const &&; |
(2) | (since C++17) |
If *this contains a value, returns a reference to the contained value.
Otherwise, throws a std::bad_optional_access exception.
Parameters
(none).
Return value
A reference to the contained value.
Exceptions
std::bad_optional_access if *this does not contain a value.
Notes
The dereference operator operator*() does not check if this optional contains a value, which may be more efficient than value().
Example
#include <optional>
#include <iostream>
int main()
{
std::optional<int> opt = {};
try {
[[maybe_unused]] int n = opt.value();
} catch(const std::bad_optional_access& e) {
std::cout << e.what() << '\n';
}
try {
opt.value() = 42;
} catch(const std::bad_optional_access& e) {
std::cout << e.what() << '\n';
}
opt = 43;
std::cout << *opt << '\n';
opt.value() = 44;
std::cout << opt.value() << '\n';
}
Output:
bad optional access bad optional access 43 44
See also
| returns the contained value if available, another value otherwise (public member function) |
|
| accesses the contained value (public member function) |
|
|
(C++17)
|
exception indicating checked access to an optional that doesn't contain a value (class) |
© cppreference.com
Licensed under the Creative Commons Attribution-ShareAlike Unported License v3.0.
https://en.cppreference.com/w/cpp/utility/optional/value
