std::make_signed(3)

NAME
std::make_signed - std::make_signed

Synopsis
   Defined in header <type_traits>
   template< class T > (since C++11)
   struct make_signed;
   If T is an integral (except bool) or enumeration type, provides the member typedef
   type which is the signed integer type corresponding to T, with the same
   cv-qualifiers.
   If T is signed or unsigned char, short, int, long, long long, the signed type from
   this list corresponding to T is provided.
   If T is an enumeration type or char, wchar_t
   , char8_t
   (since C++20), char16_t, char32_t, the signed integer type with the smallest rank
   having the same sizeof as T is provided.
   Otherwise, the behavior is undefined. (until C++20)
   Otherwise, the program is ill-formed. (since C++20)
   If the program adds specializations for std::make_signed, the behavior is undefined.

Member types
   Name Definition
   type the signed integer type corresponding to T

Helper types
   template< class T > (since C++14)
   using make_signed_t = typename make_signed<T>::type;

Example
// Run this code
 #include <type_traits>
 enum struct E : unsigned short {};
 int main()
 {
     using char_type = std::make_signed_t<unsigned char>;
     using int_type = std::make_signed_t<unsigned int>;
     using long_type = std::make_signed_t<volatile unsigned long>;
     using enum_type = std::make_signed_t<E>;
     static_assert(
         std::is_same_v<char_type, signed char> and
         std::is_same_v<int_type, signed int> and
         std::is_same_v<long_type, volatile signed long> and
         std::is_same_v<enum_type, signed short>
     );
 }

See also
   is_signed checks if a type is a signed arithmetic type
   (C++11) (class template)
   is_unsigned checks if a type is an unsigned arithmetic type
   (C++11) (class template)
   make_unsigned makes the given integral type unsigned
   (C++11) (class template)