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std::is_pointer_interconvertible_with_class

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Defined in header <type_traits>
template< class S, class M >
constexpr bool is_pointer_interconvertible_with_class( M S::* mp ) noexcept;
 (since C++20)

Given an object s of type S, determines whether s.*mp refers to a subobject of s and s is pointer-interconvertible with its subobject s.*mp. The program is ill-formed if S is not a complete type.

If S is not a StandardLayoutType, or M is not an object type, or mp is equal to nullptr, the result is always false.

Contents

[edit] Parameters

mp - a pointer-to-member to detect

[edit] Return value

true if s.*mp refers a subobject of s and s is pointer-interconvertible with its subobject s.*mp, otherwise false, where s is an object of type S.

[edit] Notes

The type of a pointer-to-member expression &S::m is not always M S::*, where m is of type M, because m may be a member inherited from a base class of S. The template arguments can be specified in order to avoid potentially surprising results.

If there is a value mp of type M S::* such that std::is_pointer_interconvertible_with_class(mp) == true, then reinterpret_cast<M&>(s) has well-defined result and it refers the same subobject as s.*mp, where s is a valid lvalue of type S.

On common platforms, the bit pattern of mp is all zero if std::is_pointer_interconvertible_with_class(mp) == true.

Feature-test macro Value Std Feature
__cpp_lib_is_pointer_interconvertible 201907L (C++20) Pointer-interconvertibility traits:

[edit] Example

Run this code
#include <type_traits>
 
struct Foo { int x; };
struct Bar { int y; };
 
struct Baz : Foo, Bar {}; // not standard-layout
 
static_assert( not std::is_same_v<decltype(&Baz::x), int Baz::*> );
static_assert( std::is_pointer_interconvertible_with_class(&Baz::x) );
static_assert( not std::is_pointer_interconvertible_with_class<Baz, int>(&Baz::x) );
 
int main() { }

[edit] See also

(C++11)
 checks if a type is a standard-layout type
(class template) [edit]
(C++11)
 checks if a type is a non-static member object pointer
(class template) [edit]
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