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std::variant_npos(3) C++ Standard Libary std::variant_npos(3) NAME std::variant_npos - std::variant_npos Synopsis Defined in header <variant> inline constexpr std::size_t variant_npos = -1; (since C++17) This is a special value equal to the largest value representable by the type std::size_t, used as the return value of index() when value- less_by_exception() is true // Run this code #include <iostream> #include <stdexcept> #include <string> #include <variant> struct Demon { Demon(int) {} Demon(const Demon&) { throw std::domain_error("copy ctor"); } Demon& operator= (const Demon&) = default; }; int main() { std::variant<int, Demon> var{42}; std::cout << std::boolalpha << "index == npos: " << (var.index() == std::variant_npos) << '\n'; try { var = Demon{666}; } catch (const std::domain_error& ex) { std::cout << "Exception: " << ex.what() << '\n' << "index == npos: " << (var.index() == std::variant_npos) << '\n' << "valueless: " << var.valueless_by_exception() << '\n'; } } Possible output: index == npos: false Exception: copy ctor index == npos: true valueless: true See also returns the zero-based index of the alterna- tive held by the index variant (public member function) valueless_by_exception checks if the variant is in the invalid state (public member function) http://cppreference.com 2022.07.31 std::variant_npos(3)
NAME | Synopsis | Possible output: | See also
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