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std::is_unsigned

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

std::is_unsigned is a UnaryTypeTrait.

If T is an arithmetic type, provides the member constant value equal to 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.

The behavior of a program that adds specializations for std::is_unsigned or std::is_unsigned_v is undefined.

Template parameters

T - a type to check

Helper variable template

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

Inherited from std::integral_constant

Member constants

value
[static]
true if T is an unsigned integral type, false otherwise
(public static member constant)

Member functions

operator bool
converts the object to bool, returns value
(public member function)
operator()
(C++14)
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_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

#include <iostream>
#include <type_traits>
 
class A {};
static_assert(std::is_unsigned_v<A> == false);
 
enum B : unsigned {};
static_assert(std::is_unsigned_v<B> == false);
 
enum class C : unsigned {};
static_assert(std::is_unsigned_v<C> == false);
 
struct S { unsigned p : 1; int q : 1; };
static_assert(
    std::is_unsigned_v<decltype(S::p)> not_eq
    std::is_unsigned_v<decltype(S::q)>
);
 
static_assert(
    std::is_unsigned_v<float> == false &&
    std::is_unsigned_v<signed int> == false &&
    std::is_unsigned_v<unsigned int> == true &&
    std::is_unsigned_v<bool> == true
);
 
int main() 
{
    std::cout << std::boolalpha << std::is_unsigned<char>::value << '\n';
}

Possible output:

false

See also

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

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https://en.cppreference.com/w/cpp/types/is_unsigned