std::is_layout_compatible
Defined in header <type_traits>
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||
template< class T, class U > struct is_layout_compatible; |
(since C++20) | |
If T
and U
are layout-compatible types, provides the member constant value
equal to true. Otherwise value
is false.
Every type is layout-compatible with its any cv-qualified versions, even if it is not an object type.
T
and U
shall each be a complete type, (possibly cv-qualified) void, or an array of unknown bound. Otherwise, the behavior is undefined.
If an instantiation of a template above depends, directly or indirectly, on an incomplete type, and that instantiation could yield a different result if that type were hypothetically completed, the behavior is undefined.
The behavior of a program that adds specializations for is_layout_compatible
or is_layout_compatible_v
is undefined.
Helper variable template
template< class T, class U > inline constexpr bool is_layout_compatible_v = is_layout_compatible<T, U>::value; |
(since C++20) | |
Inherited from std::integral_constant
Member constants
value [static] |
true if T and U are layout-compatible, 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 signed integer type and its unsigned counterpart are not layout-compatible. char is layout-compatible with neither signed char nor unsigned char.
Similar types are not layout-compatible if they are not the same type after ignoring top-level cv-qualification.
An enumeration type and its underlying type are not layout-compatible.
Array types of layout-compatible but different element types (ignoring cv-qualification) are not layout-compatible, even if they are of equal length.
Example
#include <type_traits> #include <iostream> struct Foo { int x; char y; }; class Bar { const int u = 42; volatile char v = '*'; }; enum E0 : int {}; enum class E1 : int {}; int main() { std::cout << std::boolalpha << std::is_layout_compatible_v<const void, volatile void> << '\n' << std::is_layout_compatible_v<Foo, Bar> << '\n' << std::is_layout_compatible_v<Foo[2], Bar[2]> << '\n' << std::is_layout_compatible_v<int, E0> << '\n' << std::is_layout_compatible_v<E0, E1> << '\n' << std::is_layout_compatible_v<long, unsigned long> << '\n' << std::is_layout_compatible_v<char*, const char*> << '\n' << std::is_layout_compatible_v<char*, char* const> << '\n'; }
Output:
true true false false true false false true
See also
(C++11) |
checks if a type is a standard-layout type (class template) |