std::is_standard_layout (3) - Linux Man Pages

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

See also


is_trivially_copyable checks if a type is trivially copyable
                             (class template)
(C++11)


is_pod checks if a type is a plain-old data (POD) type
                             (class template)
(C++11)(deprecated in C++20)
                             byte offset from the beginning of a standard-layout type to specified member
offsetof (function macro)