std::is_standard_layout

Header: <type_traits>

std::is_standard_layout is a UnaryTypeTrait.

# Declarations

template< class T >
struct is_standard_layout;

(since C++11)

# Notes

A pointer to a standard-layout class may be converted (with reinterpret_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

#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

# See also

• is_trivially_copyable
• is_pod
• offsetof
• standard-layout