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.
| T | - | a type to check |
template< class T > inline constexpr bool is_signed_v = is_signed<T>::value; | (since C++17) |
| value
[static] | true if T is a signed arithmetic type , false otherwise (public static member constant) |
| operator bool | converts the object to bool, returns value (public member function) |
| operator()
(C++14) | returns value (public member function) |
| Type | Definition |
|---|---|
value_type | bool |
type | std::integral_constant<bool, value> |
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()
{
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
|
(C++11) | checks if a type is an unsigned arithmetic type (class template) |
|
[static] | identifies signed types (public static member constant of std::numeric_limits<T>) |
|
(C++11) | checks if a type is an arithmetic type (class template) |
|
(C++11) | makes the given integral type signed (class template) |
|
(C++11) | makes the given integral type unsigned (class template) |
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