std::is_unsigned (3) - Linux Manuals

std::is_unsigned: std::is_unsigned

NAME

std::is_unsigned - std::is_unsigned

Synopsis

Defined in header <type_traits>
template< class T > (since C++11)
struct is_unsigned;

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

Inherited from std::integral_constant

Member constants

value true if T is an unsigned 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_unsigned : std::integral_constant<bool, T(0) < T(-1)> {};

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

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

Example

// Run this code

  #include <iostream>
  #include <type_traits>

  class A {};
  enum B : unsigned {};
  enum class C : unsigned {};

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

Output:

  false
  false
  false
  true
  false
  false