std::is_signed - cppreference.com (original) (raw)

| | | | | --------------------------------------- | | ------------- | | template< class T > struct is_signed; | | (since C++11) |

std::is_signed is a UnaryTypeTrait.

Checks whether T is a signed arithmetic type.

• If std::is_arithmetic<T>::value is true, provides the member constant value equal to T(-1) < T(0).
• Otherwise, provides the member constant value equal to false.

If the program adds specializations for std::is_signed or std::is_signed_v, the behavior is undefined.

Contents

• 1 Template parameters
• 2 Helper variable template
• 3 Inherited from std::integral_constant
  • 3.1 Member constants
  • 3.2 Member functions
  • 3.3 Member types
  • 3.4 Possible implementation
  • 3.5 Example
  • 3.6 Defect reports
  • 3.7 See also

[edit] Template parameters

[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

| | true if T is a signed arithmetic type, false otherwise (public static member constant) | | ----------------------------------------------------------------------------------------- |

Member functions

| | converts the object to bool, returns value (public member function) | | ---------------------------------------------------------------------- | | | returns value (public member function) |

Member types

[edit] Possible implementation

namespace detail { template<typename T, bool = std::is_arithmetic::value> struct is_signed : std::integral_constant<bool, T(-1) < T(0)> {};   template struct is_signed<T, false> : std::false_type {}; }   template struct is_signed : detail::is_signed::type {};

[edit] Example

#include #include   class A {}; static_assert(std::is_signed_v == false);   class B { int i; }; static_assert(std::is_signed_v == false);   enum C : int {}; static_assert(std::is_signed_v == false);   enum class D : int {}; static_assert(std::is_signed_v == false);   static_assert ( std::is_signed::value == true and // C++11 std::is_signed() == true and // C++11 std::is_signed{} == true and // C++11 std::is_signed_v == true and // C++17 std::is_signed_v == false and std::is_signed_v == true and std::is_signed_v == false and std::is_signed_v == true and std::is_signed_v == false );   int main() { // signedness of char is implementation-defined: std::cout << std::boolalpha << std::is_signed_v << '\n'; }

Possible output:

[edit] Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

[edit] See also

| | checks if a type is an unsigned arithmetic type (class template) [edit] | | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | | identifies signed types (public static member constant of std::numeric_limits) [edit] | | | checks if a type is an arithmetic type (class template) [edit] | | | obtains the corresponding signed type for the given integral type (class template) [edit] | | | obtains the corresponding signed type for the given integral type (class template) [edit] |