std::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.

The behavior of a program that adds specializations for is_scalar or is_scalar_v (since C++17) is undefined.

Template parameters

Helper variable template

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

#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';
}

T is a scalar
T is not a scalar

See also