Std::is_standard_layout (3) Linux Manual Page

std::is_standard_layout – std::is_standard_layout

Synopsis

Defined in header<type_traits>

    template <class T>
    (since C++ 11)

        struct is_standard_layout;

If T is a standard layout type (that is, a scalar type, a standard-layout class, or an array of such type/class, possibly cv-qualified), provides the member constant value equal true. For any other type, value is false.
A standard-layout_class is a class that satisfies StandardLayoutType.
The behavior is undefined if std::remove_all_extents_t<T> is an incomplete type and not (possibly cv-qualified) void.

Template parameters

T – a type to check

Helper variable template

template< class T > (since C++17)
inline constexpr bool is_standard_layout_v = is_standard_layout<T>::value;

Inherited from std::integral_constant

Member constants

value true if T is a standard-layout type , false otherwise
(public static member constant)
[static]

Member functions

converts the object to bool, returns value
operator bool (public member function)

operator() returns value
(public member function)
(C++14)

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 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 can only be used with standard-layout classes.

Example

// Run this code

#include <iostream>

#include <type_traits>
struct A {
    int m;
};
struct B {
    int m1;

  private:
    int m2;
};
struct C {
    virtual void foo();
};
int main()

{
    std::cout << std::boolalpha;
    std::cout << std::is_standard_layout<A>::value << '\n';
    std::cout << std::is_standard_layout<B>::value << '\n';
    std::cout << std::is_standard_layout<C>::value << '\n';
}

Output:

  true
  false
  false

std::is_standard_layout (3) Linux Manual Page