std::is_signed (3) - Linux Manuals

std::is_signed: std::is_signed


std::is_signed - std::is_signed


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)

Member functions

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

operator() returns value
              (public member function)

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 {};


// 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';



See also

is_unsigned checks if a type is an unsigned arithmetic type
              (class template)

is_signed identifies signed types
              (public static member constant of std::numeric_limits<T>)

is_arithmetic checks if a type is an arithmetic type
              (class template)

make_signed makes the given integral type signed
              (class template)

make_unsigned makes the given integral type unsigned
              (class template)