std::is_standard_layout
std::is_standard_layout
Defined in header <type_traits>
|
||
---|---|---|
|
(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
.
Template parameters
T | - | a type to check |
Helper variable template
|
(since C++17) |
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>
|
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
#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
(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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