| 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.
Template parameters
| T | - | a type to check |
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> |
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
#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
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) |
| (C++11) | 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) |
| (C++11) | makes the given integral type unsigned (class template) |
| std::experimental::is_signed_v
(library fundamentals TS) | variable template alias of std::is_signed::value (variable template) |
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