std::is_scalar (3) - Linux Manuals

std::is_scalar: std::is_scalar

NAME

std::is_scalar - std::is_scalar

Synopsis

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

If T is a scalar_type (that is a possibly cv-qualified arithmetic, pointer, pointer_to_member, enumeration, or std::nullptr_t 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 > (since C++17)
inline constexpr bool is_scalar_v = is_scalar<T>::value;

Inherited from std::integral_constant

Member constants

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

Member functions

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

operator() returns value
              (public member function)
(C++14)

Member types

Type Definition
value_type bool
type std::integral_constant<bool, value>

Notes

Each individual memory location in the C++ memory model, including the hidden memory locations used by language features (e.g virtual table pointer), has scalar type (or is a sequence of adjacent bit-fields of non-zero length). Sequencing of side-effects in expression evaluation, interthread synchronization, and dependency ordering are all defined in terms of individual scalar objects.

Possible implementation

  template< class T >
  struct is_scalar : std::integral_constant<bool,
                       std::is_arithmetic<T>::value ||
                       std::is_enum<T>::value ||
                       std::is_pointer<T>::value ||
                       std::is_member_pointer<T>::value ||
                       std::is_null_pointer<T>::value> {};

Example

// Run this code

  #include <iostream>
  #include <type_traits>

  int main() {
      class cls {};
      std::cout << (std::is_scalar<int>::value
                       ? "T is a scalar"
                       : "T is not a scalar") << '\n';
      std::cout << (std::is_scalar<cls>::value
                       ? "T is a scalar"
                       : "T is not a scalar") << '\n';
  }

Output:

  T is a scalar
  T is not a scalar