std::is_scalar

Defined in header <type_traits>

template< class T >
struct is_scalar;

(since C++11)

If T is a scalar type (that is, arithmetic type, enumeration type, pointer, pointer to member, or std::nullptr_t, including any cv-qualified variants), provides the member constant value equal true. For any other type, value is false.

Template parameters

a type to check

Helper variable template

template< class T >
constexpr bool is_scalar_v = is_scalar<T>::value;

(since C++17)

Inherited from std::integral_constant

Member constants

value

[static]

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

Member functions

operator bool	converts the object to `bool`, returns `value` (public member function)
operator() (C++14)	returns `value` (public member function)

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_same<std::nullptr_t, typename std::remove_cv<T>::type>::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';
}

Output:

T is a scalar
T is not a scalar

is_arithmetic (C++11)	checks if a type is arithmetic type (class template)
is_enum (C++11)	checks if a type is an enumeration type (class template)
is_pointer (C++11)	checks if a type is a pointer type (class template)
is_member_pointer (C++11)	checks if a type is a pointer to a non-static member function or object (class template)
std::experimental::is_scalar_v (library fundamentals TS)	variable template alias of `std::is_scalar::value` (variable template)

Links:

http://en.cppreference.com/w/cpp/types/is_scalar

doc_CPP

2025-01-10 15:47:30

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