std::is_unsigned - cppreference.com
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    std::is_unsigned

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

    std::is_unsigned is a UnaryTypeTrait.

    Checks whether T is an unsigned arithmetic type.

    • If std::is_arithmetic<T>::value is true, provides the member constant value equal to T(0) < T(-1).
    • Otherwise, provides the member constant value equal to false.

    If the program adds specializations for std::is_unsigned or std::is_unsigned_v, the behavior is undefined.

    Template parameters

    T - a type to check

    Helper variable template

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

    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

    Run this code
    #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() 
{
    // signedness of char is implementation-defined:
    std::cout << std::boolalpha << std::is_unsigned<char>::value << '\n';
}

    Possible output: 

    false

    Defect reports

    The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

    DR Applied to Behavior as published Correct behavior
    LWG 2197 C++11 value could be true even if T is not an arithmetic type can only be false in this case

    See also