std::is_scalar

 

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Type traits

Type traits (since C++11)

Type categories is_void is_null_pointer (DR*) is_reflection (C++26) is_array is_pointer is_enum is_union is_class is_function is_reference      is_object is_scalar is_compound is_integral is_floating_point      is_fundamental is_arithmetic is_lvalue_reference is_rvalue_reference is_member_pointer is_member_object_pointer is_member_function_pointer Type properties is_const is_volatile is_empty is_polymorphic is_final (C++14) is_abstract is_aggregate (C++17) is_implicit_lifetime (C++23) is_trivial (deprecated in C++26) is_trivially_copyable is_standard_layout is_literal_type (until C++20*) is_pod (deprecated in C++20) is_signed is_unsigned is_bounded_array (C++20) is_unbounded_array (C++20) is_scoped_enum (C++23) has_unique_object_representations (C++17)     Type trait constants integral_constantbool_constanttrue_typefalse_type (C++17) Metafunctions conjunction (C++17) disjunction (C++17) negation (C++17)

Supported operations is_constructibleis_trivially_constructibleis_nothrow_constructible is_default_constructibleis_trivially_default_constructibleis_nothrow_default_constructible is_copy_constructibleis_trivially_copy_constructibleis_nothrow_copy_constructible is_move_constructibleis_trivially_move_constructibleis_nothrow_move_constructible is_assignableis_trivially_assignableis_nothrow_assignable is_copy_assignableis_trivially_copy_assignableis_nothrow_copy_assignable is_move_assignableis_trivially_move_assignableis_nothrow_move_assignable is_destructibleis_trivially_destructibleis_nothrow_destructible has_virtual_destructor is_swappable_withis_swappableis_nothrow_swappable_withis_nothrow_swappable (C++17)(C++17)(C++17)(C++17) Relationships and property queries is_same is_convertibleis_nothrow_convertible (C++20) is_layout_compatible (C++20) is_pointer_interconvertible_base_of (C++20) is_pointer_interconvertible_with_class (C++20)     is_corresponding_member (C++20) reference_constructs_from_temporary (C++23) reference_converts_from_temporary (C++23) is_base_of is_virtual_base_of (C++26) alignment_of rank extent is_invocableis_invocable_ris_nothrow_invocableis_nothrow_invocable_r (C++17)(C++17)(C++17)(C++17) Type modifications remove_cvremove_constremove_volatile add_cvadd_constadd_volatile make_signed make_unsigned remove_reference add_lvalue_referenceadd_rvalue_reference remove_pointer add_pointer remove_extent remove_all_extents Type transformations aligned_storage (deprecated in C++23) aligned_union (deprecated in C++23) decay remove_cvref (C++20) result_ofinvoke_result (until C++20*)(C++17) conditional common_type common_reference (C++20) underlying_type type_identity (C++20) enable_if void_t (C++17)

 

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

std::is_scalar is a UnaryTypeTrait.

If T is a scalar type, provides the member constant value equal true. For any other type, value is false.

If the program adds specializations for std::is_scalar or std::is_scalar_v, the behavior is undefined.

Template parameters

T

-

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, inter-thread 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 #if __cpp_impl_reflection > 0 || std::is_reflection_v<T> #endif > {};

Example

Run this code

#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

See also

is_arithmetic (C++11)	checks if a type is an 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)