NAME

std::is_corresponding_member - std::is_corresponding_member

Synopsis

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 ) (since C++20)
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

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 checks if a type is a standard-layout type
(C++11) (class template)
is_layout_compatible checks if two types are layout-compatible
(C++20) (class template)
is_member_object_pointer checks if a type is a pointer to a non-static member object
(C++11) (class template)