Std::is_unsigned (3) Linux Manual Page

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

std::is_unsigned (3) Linux Manual Page