std::optional::begin - cppreference.com (original) (raw)

| 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.

[edit] Return value

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

[edit] Complexity

Constant.

[edit] Notes

[edit] Example

#include #include #include   int main() { constexpr std::optional none{std::nullopt}; constexpr std::optional 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> 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]

[edit] See also

| | returns an iterator to the end (public member function) [edit] | | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |