Std::is_signed (3) Linux Manual Page

std::is_signed – std::is_signed

Synopsis

Defined in header<type_traits>

    template <class T>
    (since C++ 11)

        struct is_signed;

If T is an arithmetic type, provides the member constant value equal true if T(-1) < T(0): this results in true for the floating-point types and the signed integer types, and in false for the unsigned integer types and the type bool.
For any other type, value is false.

Template parameters

T – a type to check

Helper variable template

template< class T > (since C++17)
inline constexpr bool is_signed_v = is_signed<T>::value;

Inherited from std::integral_constant

Member constants

value true if T is a signed arithmetic type , false otherwise
(public static member constant)
[static]

Member functions

converts the object to bool, returns value
operator bool (public member function)

operator() returns value
(public member function)
(C++14)

Member types

Type Definition
value_type bool
type std::integral_constant<bool, value>

Possible implementation

  namespace detail {
  template<typename T,bool = std::is_arithmetic<T>::value>
  struct is_signed : std::integral_constant<bool, T(-1) < T(0)> {};

  template<typename T>
  struct is_signed<T,false> : std::false_type {};
  } // namespace detail

template<typename T>
struct is_signed : detail::is_signed<T>::type {};

Example

// Run this code

#include <iostream>

#include <type_traits>
class A
{
};

enum B : int {};

enum class C : int {};
int main()

{
    std::cout << std::boolalpha;
    std::cout << std::is_signed<A>::value << '\n';
    std::cout << std::is_signed<float>::value << '\n';
    std::cout << std::is_signed<signed int>::value << '\n';
    std::cout << std::is_signed<unsigned int>::value << '\n';
    std::cout << std::is_signed<B>::value << '\n';
    std::cout << std::is_signed<C>::value << '\n';
    // shorter:
    std::cout << std::is_signed<signed int>() << '\n';
    std::cout << std::is_signed<unsigned int>() << '\n';
}

Output:

  false
  true
  true
  false
  false
  false
  true
  false

is_unsigned checks if a type is an unsigned arithmetic type
              (class template)
(C++11)
is_signed identifies signed types
              (public static member constant of std::numeric_limits<T>)
[static]
is_arithmetic checks if a type is an arithmetic type
              (class template)
(C++11)
make_signed makes the given integral type signed
              (class template)
(C++11)
make_unsigned makes the given integral type unsigned
              (class template)
(C++11)

std::is_signed (3) Linux Manual Page