std::optional Defined in header<optional> template<classT> classoptional; (since C++17) The class templatestd::optionalmanages an optional contained value, i.e. a value that may or may not be present. A common
#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()); // 支持范围 for 循环 for (int ...
std::optional From cppreference.com Defined in header<optional> template<classT> classoptional; (since C++17) The class templatestd::optionalmanages an optional contained value, i.e. a value that may or may not be present. A common use case foroptionalis the return value of a function tha...
std::optional<T>::optional constexproptional()noexcept; (1)(since C++17) constexproptional(std::nullopt_t)noexcept; (2)(since C++17) constexproptional(constoptional&other); (3)(since C++17) constexproptional(optional&&other)noexcept(/* see below */); ...
optional(C++17) expected(C++23) variant(C++17)−any(C++17) bitset−Bit manipulation(C++20) Containers library vector−deque−array(C++11) list−forward_list(C++11) inplace_vector(C++26) hive(C++26) map−multimap−set−multiset ...
optional(C++17) expected(C++23) variant(C++17)−any(C++17) bitset−Bit manipulation(C++20) Containers library vector−deque−array(C++11) list−forward_list(C++11) inplace_vector(C++26) hive(C++26) map−multimap−set−multiset ...
optional(C++17) expected(C++23) variant(C++17)−any(C++17) bitset−Bit manipulation(C++20) Containers library vector−deque−array(C++11) list−forward_list(C++11) inplace_vector(C++26) hive(C++26) map−multimap−set−multiset ...
optional(C++17)−any(C++17) variant(C++17)−format(C++20) 文字列ライブラリ basic_string basic_string_view(C++17) ヌル終端文字列: バイト−マルチバイト−ワイド コンテナライブラリ array(C++11)−vector map−unordered_map(C++11) ...
optional(C++17) expected(C++23) variant(C++17)−any(C++17) bitset−Bit manipulation(C++20) Containers library vector−deque−array(C++11) list−forward_list(C++11) inplace_vector(C++26) hive(C++26) map−multimap−set−multiset ...
optional(C++17) expected(C++23) variant(C++17)−any(C++17) bitset−Bit manipulation(C++20) Containers library vector−deque−array(C++11) list−forward_list(C++11) inplace_vector(C++26) hive(C++26) map−multimap−set−multiset ...