std::is_standard_layout (3) - Linux Manuals

std::is_standard_layout: std::is_standard_layout

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;

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