NAME¶

std::is_signed - std::is_signed

Synopsis¶

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

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 is_signed
or is_signed_v
(since C++17) is undefined.

Template parameters¶

T - a type to check

Helper variable template

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

Inherited from std::integral_constant

Member constants¶

value true if T is a signed arithmetic type , false otherwise
[static] (public static member constant)

Member functions¶

operator bool converts the object to bool, returns value
(public member function)
operator() returns value
(C++14) (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()
{
std::cout << std::boolalpha;
std::cout << std::is_signed<A>::value << '\n'; // false
std::cout << std::is_signed<float>::value << '\n'; // true
std::cout << std::is_signed<signed int>::value << '\n'; // true
std::cout << std::is_signed<unsigned int>::value << '\n'; // false
std::cout << std::is_signed<B>::value << '\n'; // false
std::cout << std::is_signed<C>::value << '\n'; // false

// shorter:
std::cout << std::is_signed_v<bool> << '\n'; // false
std::cout << std::is_signed<signed int>() << '\n'; // true
std::cout << std::is_signed<unsigned int>{} << '\n'; // false
}

Output:¶

false
true
true
false
false
false
false
true
false

See also¶

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