std::optional<T>::begin

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.

Return value

Iterator to the contained value if has_value() is true. Otherwise, a past-the-end iterator.

Complexity

Constant.

Notes

Feature-test macro	Value	Std	Feature
`__cpp_lib_optional_range_support`	`202406L`	(C++26)	Range support for `std::optional`

Example

#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]

std::optional<T>::begin

Return value

Complexity

Notes

Example

See also