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std::is_scalar

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

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.

Contents

[edit] Template parameters

T - a type to check

[edit] Helper variable template

template< class T >
inline 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>

[edit] 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.

[edit] 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> {};

[edit] Example

#include <iostream>
#include <type_traits>
#include <typeinfo>
#include <utility>
 
template <typename Head, typename... Tail>
void are_scalars(Head&& head, Tail&&... tail) {
    using T = std::decay_t<decltype(head)>;
    std::cout << typeid(T).name() << " is "
              << ( std::is_scalar_v<T> ? "" : "not " )
              << "a scalar\n";
    if constexpr (sizeof... (Tail)) {
        are_scalars(std::forward<decltype(tail)>(tail)...);
    }
}
 
int main() {
    struct S { int m; } s;
    int S::* mp = &S::m;
    enum class E { e };
    are_scalars(42, 3.14, E::e, "str", mp, nullptr, s);
}

Possible output:

int is a scalar
double is a scalar
main::E is a scalar
char const* is a scalar
int main::S::* is a scalar
nullptr is a scalar
main::S is not a scalar

[edit] See also

checks if a type is an arithmetic type
(class template) [edit]
(C++11)
checks if a type is an enumeration type
(class template) [edit]
checks if a type is a pointer type
(class template) [edit]
checks if a type is a pointer to an non-static member function or object
(class template) [edit]