std::is_signed

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

If T is a signed arithmetic type, provides the member constant value equal true. For any other type, value is false.

Contents

[edit] Template parameters

T - a type to check

[edit] Helper variable template

template< class T >
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>

[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

#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

(C++11)
checks if a type is unsigned arithmetic type
(class template)
[static]
identifies signed types
(public static member constant of std::numeric_limits)
checks if a type is floating-point type
(class template)
(C++11)
checks if a type is integral type
(class template)
(C++11)
makes the given integral type signed
(class template)
makes the given integral type unsigned
(class template)
(library fundamentals TS)
variable template alias of std::is_signed::value
(variable template)