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std::is_unsigned

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

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 is_unsigned or is_unsigned_v (since C++17) is undefined.

Template parameters

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

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

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