std::is_corresponding_member

 

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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>
#include <iostream>
 
struct Foo { int x; };
struct Bar { int y; double z; };
 
struct Baz : Foo, Bar {}; // not standard-layout
 
int main()
{
    std::cout << std::boolalpha
        << std::is_same_v<decltype(&Baz::x), int Foo::*> << '\n'
        << std::is_same_v<decltype(&Baz::y), int Bar::*> << '\n'
        << std::is_corresponding_member(&Foo::x, &Bar::y) << '\n'
        << std::is_corresponding_member(&Baz::x, &Baz::y) << '\n'
        << std::is_corresponding_member<Baz, Baz, int, int>(&Baz::x, &Baz::y) << '\n';
}

Output:

true
true
true
true
false

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)