# std::is_corresponding_member

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< cpp‎ | types

Defined in header `<type_traits>` |  |
template< class S1, class S2, class M1, class M2 > constexpr bool is_corresponding_member( M1 S1::* mp, M2 S2::* mq ) noexcept; |  | (since C++20)

Determines whether mp and mq refer corresponding members in the common initial sequence of `S1` and `S2`. The program is ill-formed if either `S1` or `S2` is an incomplete type.

If either `S1` or `S2` is not a StandardLayoutType, or either `M1` or `M2` is not an object type, or either mp or mq is equal to nullptr, the result is always false.

### Parameters

mp, mq | - | pointers-to-member to detect

### Return value

true if mp and mq refer corresponding members in the common initial sequence of `S1` and `S2`, otherwise false.

### 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.

### Example

Run this code

    #include <type_traits>

    struct Foo { int x; };

    struct Bar
    {
        int y;
        double z;
    };

    struct Baz : Foo, Bar {}; // not standard-layout

    static_assert(
        std::is_same_v<decltype(&Baz::x), int Foo::*> == true &&
        std::is_same_v<decltype(&Baz::y), int Bar::*> == true &&
        std::is_corresponding_member(&Foo::x, &Bar::y) == true &&
        std::is_corresponding_member(&Baz::x, &Baz::y) == true &&
        std::is_corresponding_member<Baz, Baz, int, int>(&Baz::x, &Baz::y) == false
    );

    int main() {}

### See also

is_standard_layout (C++11) | checks if a type is a standard-layout type (class template)
is_layout_compatible (C++20) | checks if two types are layout-compatible (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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