Defined in header <type_traits> | ||
---|---|---|
template< class T > struct is_standard_layout; | (since C++11) |
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
.
T | - | a type to check |
template< class T > inline constexpr bool is_standard_layout_v = is_standard_layout<T>::value; | (since C++17) |
value
[static] | true if T is a standard-layout type , false otherwise (public static member constant) |
operator bool | converts the object to bool , returns value (public member function) |
operator()
(C++14) | returns value (public member function) |
Type | Definition |
---|---|
value_type | bool |
type | std::integral_constant<bool, value> |
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.
#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
(C++11) | checks if a type is trivially copyable (class template) |
(C++11)(deprecated in C++20) | checks if a type is a plain-old data (POD) type (class template) |
byte offset from the beginning of a standard-layout type to specified member (function macro) |
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