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Showing content from https://cplusplus.com/reference/type_traits/make_signed/ below:

class template

<type_traits>

std::make_signed

template <class T> struct make_signed;

Make signed

Obtains the signed type corresponding to T, keeping any cv-qualifiers.

The transformed type is aliased as member type make_signed::type as follows:

If T is an unsigned integral type, this is the corresponding signed type.
If T is already a signed integral type, this is T unchanged.
If T is an enumeration type, this is the smallest signed integer type with the same size as T (as per sizeof operator).

Notice that this class merely obtains a type using another type as model, but it does not transform values or objects between those types. To explicitly cast an integral type to its signed equivalent, you can use static_cast.

Template parameters

T: An integer type (except bool), or an enumeration type.

Member types member type definition type Signed type corresponding to T.
Example

// make_signed
#include <iostream>
#include <type_traits>

enum ENUM1 {a,b,c};
enum class ENUM2 : unsigned char {x,y,z};

int main() {
  typedef std::make_signed<int>::type A;                // int
  typedef std::make_signed<unsigned>::type B;           // int
  typedef std::make_signed<const unsigned>::type C;     // const int
  typedef std::make_signed<ENUM1>::type D;              // int
  typedef std::make_signed<ENUM2>::type E;              // signed char

  std::cout << std::boolalpha;
  std::cout << "typedefs of int:" << std::endl;
  std::cout << "A: " << std::is_same<int,A>::value << std::endl;
  std::cout << "B: " << std::is_same<int,B>::value << std::endl;
  std::cout << "C: " << std::is_same<int,C>::value << std::endl;
  std::cout << "D: " << std::is_same<int,D>::value << std::endl;
  std::cout << "E: " << std::is_same<int,E>::value << std::endl;

  return 0;
}

Output:

typedefs of int:
A: true
B: true
C: false
D: true
E: false