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std::is_standard_layout(3) C++ Standard Libary std::is_standard_layout(3) NAME std::is_standard_layout - std::is_standard_layout Synopsis Defined in header <type_traits> template< class T > (since C++11) struct is_standard_layout; std::is_standard_layout is a UnaryTypeTrait. If T is a standard-layout type, provides the member constant value equal to true. For any other type, value is false. If std::remove_all_extents_t<T> is an incomplete type and not (pos- sibly cv-qualified) void, the behavior is undefined. If the program adds specializations for std::is_standard_layout or std::is_standard_layout_v, the behavior is undefined. Template parameters T - a type to check Helper variable template template< class T > inline constexpr bool is_standard_layout_v = (since C++17) is_standard_layout<T>::value; Inherited from std::integral_constant Member constants value true if T is a standard-layout type, false otherwise [static] (public static member constant) Member functions operator bool converts the object to bool, returns value (public member function) operator() returns value (C++14) (public member function) Member types Type Definition value_type bool type std::integral_constant<bool, value> Notes A pointer to a standard-layout class may be converted (with reinter- pret_cast) to a pointer to its first non-static data member and vice versa. If a standard-layout union holds two or more standard-layout structs, it is permitted to inspect the common initial part of them. The macro offsetof is only guaranteed to be usable with standard- layout classes. Example // Run this code #include <type_traits> struct A { int m; }; static_assert(std::is_standard_layout_v<A> == true); class B: public A { int m; }; static_assert(std::is_standard_layout_v<B> == false); struct C { virtual void foo(); }; static_assert(std::is_standard_layout_v<C> == false); int main() {} Defect reports The following behavior-changing defect reports were applied retroac- tively to previously published C++ standards. DR Applied to Behavior as published Correct be- havior LWG 2015 C++11 T could be an array of incomplete the behavior is class type with unknown bound undefined in this case See also is_trivially_copyable checks if a type is trivially copyable (C++11) (class template) is_pod checks if a type is a plain-old data (POD) type (C++11)(deprecated in C++20) (class template) byte offset from the beginning of a standard-layout offsetof type to specified member (function macro) http://cppreference.com 2024.06.10 std::is_standard_layout(3)
NAME | Synopsis | Template parameters | Member constants | Member functions | Member types | Notes | Example | See also
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