std::is_standard_layout
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
, that is
1. has no non-static data members that aren't standard-layout or reference
2. has no virtual functions and no virtual base classes
3. has the same access control for all non-static data members
4. has no base classes that aren't standard-layout
5. either has no base class with non-static data members or has no non-static data members in the most derived class and only one base with them
6. has no base classes of the same type as the first non-static data member
Contents |
Inherited from std::integral_constant
Member constants
value
[static]
|
true if T is a standard-layout type , false otherwise (public static member constant) |
Member functions
operator bool |
converts the object to bool, returns value (public member function) |
operator()
(C++14)
|
returns value (public member function) |
Member types
Type | Definition |
value_type
|
bool
|
type
|
std::integral_constant<bool, value> |
[edit] 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.
[edit] Example
#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
[edit] See also
(C++11)
|
checks if a type is trivially copyable (class template) |
(C++11)
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checks if a type is plain-old data (POD) type (class template) |
byte offset from the beginning of a standard-layout type to specified member (function macro) |
|
(library fundamentals TS)
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variable template alias of std::is_standard_layout::value (variable template) |