std::optional<T>::begin
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std::optional
optional::begin
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constexpr iterator begin() noexcept;
(since C++26)
constexpr const_iterator begin() const noexcept;
(since C++26)
If *this contains a value, returns an iterator to the contained value. Otherwise, a past-the-end iterator value.
Contents
[edit] Return value
Iterator to the contained value if has_value() is true. Otherwise, a past-the-end iterator.
[edit] Complexity
Constant.
[edit] Notes
| Feature-test macro | Value | Std | Feature |
|---|---|---|---|
__cpp_lib_optional_range_support |
202406L |
(C++26) | Range support for std::optional
|
[edit] Example
Run this code
#include <optional> #include <print> #include <vector> int main() { constexpr std::optional <int> none{std::nullopt }; constexpr std::optional <int> some{42}; static_assert(none.begin() == none.end()); static_assert(some.begin() != some.end()); // ranged-for loop support for (int i : none) std::println ("'none' has a value of {}", i); for (int i : some) std::println ("'some' has a value of {}", i); std::optional <std::vector <int>> many({0, 1, 2}); for (const auto& v : many) std::println ("'many' has a value of {}", v); }
Output:
'some' has a value of 42 'many' has a value of [0, 1, 2]