std::optional<T>::begin

 

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std::optional

Member functions

optional::optional

optional::~optional

optional::operator=

Observers

optional::operator->optional::operator*

optional::operator booloptional::has_value

optional::value

optional::value_or

Iterators

optional::begin (C++26)

optional::end (C++26)

Monadic operations

optional::and_then (C++23)

optional::transform (C++23)

optional::or_else (C++23)

Modifiers

optional::emplace

optional::swap

optional::reset

Non-member functions

operator==operator!=operator<operator<=operator>operator>=operator<=> (C++20)

make_optional

swap(std::optional)

Deduction guides

Helper classes

hash<std::optional>

nullopt_t

in_place_t

bad_optional_access

Helper objects

nullopt

in_place

 

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.

Parameters

(none)

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

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]

See also

end (C++26)

returns an iterator to the end (public member function)