std::is_enum

 

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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_structural (C++26) 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_enum;		(since C++11)

std::is_enum is a UnaryTypeTrait.

Checks whether T is an enumeration type. Provides the member constant value which is equal to true, if T is an enumeration type. Otherwise, value is equal to false.

If the program adds specializations for std::is_enum or std::is_enum_v, the behavior is undefined.

Template parameters

T

-

a type to check

Helper variable template

template< class T > constexpr bool is_enum_v = is_enum<T>::value;		(since C++17)

Inherited from std::integral_constant

Member constants

value [static]

true if T is an enumeration 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>

Example

Run this code

#include <type_traits>

struct A { enum E { e }; };
static_assert(!std::is_enum_v<A>);
static_assert(std::is_enum_v<A::E>);
static_assert(std::is_enum_v<decltype(A::E::e)>);

enum E {};
static_assert(std::is_enum_v<E>);
static_assert(std::is_enum_v<const E>, "Constness is ignored");
static_assert(!std::is_enum_v<E&>, "References matter");

enum class E1 : int { e };
static_assert(std::is_enum_v<E1>);
static_assert(std::is_enum_v<decltype(E1::e)>);

static_assert(!std::is_enum_v<int>);

enum class E2;
static_assert(std::is_enum_v<E2>, "Forward-declared scoped enum");

enum class E3 : char;
static_assert(std::is_enum_v<E3>, "Forward-declared scoped enum with explicit base type");

int main() {}

See also

is_integral (C++11)	checks if a type is an integral type (class template)
is_arithmetic (C++11)	checks if a type is an arithmetic type (class template)
is_scalar (C++11)	checks if a type is a scalar type (class template)
is_scoped_enum (C++23)	checks if a type is a scoped enumeration type (class template)
is_enumerator (C++26)	checks if reflection represents an enumerator (function)
is_enum_type (C++26)	checks if reflected type is an enumeration type (function)