std::is_corresponding_member

template<class S1, class S2, class M1, class M2>
constexpr bool is_corresponding_member( M1 S1::* mp, M2 S2::* mq ) noexcept;

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

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

#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';
}

true
true
true
true
false

See also