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)
   The behavior of a program that adds specializations for make_signed 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 <iostream>
 #include <type_traits>
 int main() {
     typedef std::make_signed<unsigned char>::type char_type;
     typedef std::make_signed<unsigned int>::type int_type;
     typedef std::make_signed<volatile unsigned long>::type long_type;
     bool ok1 = std::is_same<char_type, signed char>::value;
     bool ok2 = std::is_same<int_type, signed int>::value;
     bool ok3 = std::is_same<long_type, volatile signed long>::value;
     std::cout << std::boolalpha
     << "char_type is 'signed char'? : " << ok1 << '\n'
     << "int_type is 'signed int'? : " << ok2 << '\n'
     << "long_type is 'volatile signed long'? : " << ok3 << '\n';
 }

Output:
 char_type is 'signed char'? : true
 int_type is 'signed int'? : true
 long_type is 'volatile signed long'? : true

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)