# 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.

### Parameters

mp | - | a pointer-to-member to detect

### 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`.

### 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 | Comment
--- | --- | --- | ---
`__cpp_lib_is_pointer_interconvertible` | 201907L | (C++20) | Pointer-interconvertibility traits: std::is_pointer_interconvertible_base_of, `std::is_pointer_interconvertible_with_class`

### 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() { }

### See also

is_standard_layout (C++11) | checks if a type is a standard-layout type (class template)
is_member_object_pointer (C++11) | checks if a type is a pointer to a non-static member object (class template)

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