NAME¶

std::is_unsigned - std::is_unsigned

Synopsis¶

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

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.

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 > (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 integral type, false otherwise
[static] (public static member constant)

Member functions¶

operator bool converts the object to bool, returns value
(public member function)
operator() returns value
(C++14) (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()
{
std::cout << std::boolalpha << std::is_unsigned<char>::value << '\n';
}

Possible output:¶

false

See also¶

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