std::is_unsigned

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

Helper variable template

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

false

Defect reports

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

See also