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# std::is_signed

From cppreference.com
< cpp‎ | types

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 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.

### [edit] Template parameters

T | - | a type to check

### [edit] Helper variable template

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

[edit]

## 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>

### [edit] 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 {};

### [edit] Example

Run this code

    #include <iostream>
    #include <type_traits>

    class A {};
    enum B : int {};
    enum class C : int {};

    int main()
    {
        std::cout << std::boolalpha;
        std::cout << std::is_signed<A>::value << '\n';
        std::cout << std::is_signed<float>::value << '\n';
        std::cout << std::is_signed<signed int>::value << '\n';
        std::cout << std::is_signed<unsigned int>::value << '\n';
        std::cout << std::is_signed<B>::value << '\n';
        std::cout << std::is_signed<C>::value << '\n';

        // shorter:
        std::cout << std::is_signed<signed int>() << '\n';
        std::cout << std::is_signed<unsigned int>() << '\n';
    }

Output:

    false
    true
    true
    false
    false
    false
    true
    false

### [edit] See also

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

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