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Showing content from https://cplusplus.com/reference/type_traits/is_scalar/ below:

class template

<type_traits>

std::is_scalar

template <class T> struct is_scalar;

Is scalar type

Trait class that identifies whether T is a scalar type. A scalar type is a type that has built-in functionality for the addition operator without overloads (arithmetic, pointer, member pointer, enum and std::nullptr_t).

It inherits from integral_constant as being either true_type or false_type, depending on whether T is a scalar type, no matter its const and/or volative qualification.

This is a compound type trait defined with the same behavior as:

template<class T>
struct is_scalar : std::integral_constant < bool,
         is_arithmetic<T>::value || is_pointer<T>::value ||
         is_member_pointer<T>::value || is_enum<T>::value ||
         is_same<nullptr_t, typename remove_cv<T>::type>::value> {};

Template parameters

T: A type.

Member types Inherited from integral_constant:

Member constants Inherited from integral_constant:
member constant definition value either true or false
Member functions Inherited from integral_constant:

operator bool: Returns value (public member function)

Example

// is_scalar example
#include <iostream>
#include <type_traits>

class A {};

int main() {
  std::cout << std::boolalpha;
  std::cout << "is_scalar:" << std::endl;
  std::cout << "int: " << std::is_scalar<int>::value << std::endl;
  std::cout << "A: " << std::is_scalar<A>::value << std::endl;
  std::cout << "A&: " << std::is_scalar<A&>::value << std::endl;
  std::cout << "A*: " << std::is_scalar<A*>::value << std::endl;
  std::cout << "int(int): " << std::is_scalar<int(int)>::value << std::endl;
  std::cout << "int(*)(int): " << std::is_scalar<int(*)(int)>::value << std::endl;
  return 0;
}

Output:

is_scalar:
int: true
A: false
A&: false
A*: true
int(int): false
int(*)(int): true