# std::is_signed

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< cpp‎ | types

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

`std::is_signed` is an UnaryTypeTrait.

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 `std::is_signed` or `std::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

value [static] | 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)
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_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 {};

### Example

Run this code

    #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:

    true

### See also

is_unsigned (C++11) | checks if a type is an unsigned 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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