template< class T >
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 (possibly 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< class T >
constexpr bool is_standard_layout_v = is_standard_layout<T>::value;
T is a standard-layout type, false otherwise
A pointer to a standard-layout class may be converted (with reinterpret_cast) to a pointer to its first non-static data member (see empty base optimization) 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.
[edit] Example#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() {}[edit] Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
DR Applied to Behavior as published Correct behavior LWG 2015 C++11T could be an array of incomplete
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