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std::is_standard_layout(3) | C++ Standard Libary | std::is_standard_layout(3) |
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, provides the member constant value equal to
true.
For any other type, value is false.
The behavior is undefined if std::remove_all_extents_t<T> is an
incomplete type and
not (possibly cv-qualified) void.
The behavior of a program that adds specializations for is_standard_layout
or is_standard_layout_v
(since C++17) is undefined.
Template parameters¶
T - a type to check
Helper variable template
template< class T >
inline constexpr bool is_standard_layout_v = (since C++17)
is_standard_layout<T>::value;
Inherited from std::integral_constant
Member constants¶
value true if T is a standard-layout type , false otherwise
[static] (public static member constant)
Member functions¶
operator bool converts the object to bool, returns value
(public member function)
operator() returns value
(C++14) (public member function)
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 is only guaranteed to be usable 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
(C++11) (class template)
is_pod checks if a type is a plain-old data (POD) type
(C++11)(deprecated in C++20) (class template)
byte offset from the beginning of a standard-layout
offsetof type to specified member
(function macro)
2022.07.31 | http://cppreference.com |