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

If T is an arithmetic type, provides the member constant value equal to true if T(-1) < T(0): this results in true for the floating-point types and the signed integer types, and in false for the unsigned integer types and the type bool.

For any other type, value is false.

The behavior of a program that adds specializations for is_signed or is_signed_v (since C++17) is undefined.

Template parameters

T - a type to check

Helper variable template

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

Inherited from std::integral_constant

Member constants

true if T is a signed arithmetic type, false otherwise
(public static member constant)

Member functions

operator bool
converts the object to bool, returns value
(public member function)
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_signed : std::integral_constant<bool, T(-1) < T(0)> {};
    template<typename T>
    struct is_signed<T,false> : std::false_type {};
} // namespace detail
template<typename T>
struct is_signed : detail::is_signed<T>::type {};


#include <iostream>
#include <type_traits>
class A {};
enum B : int {};
enum class C : int {};
int main()
    static_assert(std::is_signed<A>::value == false);
    static_assert(std::is_signed<float>::value == true);
    static_assert(std::is_signed<signed int>::value == true);
    static_assert(std::is_signed<unsigned int>::value == false);
    static_assert(std::is_signed<B>::value == false);
    static_assert(std::is_signed<C>::value == false);
    // shorter:
    static_assert(std::is_signed_v<bool> == false);
    static_assert(std::is_signed<signed int>() == true);
    static_assert(std::is_signed<unsigned int>{} == false);
    static_assert(std::is_signed_v<signed char> == true);
    static_assert(std::is_signed_v<unsigned char> == false);
    // signedness of char is implementation-defined:
    std::cout << std::boolalpha << std::is_signed_v<char> << '\n';

Possible output:


See also

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

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