Type support (basic types, RTTI, type traits)

(See also type for type system overview).

Basic types

Fundamental types defined by the language

Additional basic types and macros

Defined in header <cstddef>
size_t	unsigned integer type returned by the sizeof operator (typedef)
ptrdiff_t	signed integer type returned when subtracting two pointers (typedef)
nullptr_t (C++11)	the type of the null pointer literal nullptr (typedef)
NULL	implementation-defined null pointer constant (macro constant)
max_align_t (C++11)	POD type with alignment requirement as great as any other scalar type (typedef)
offsetof	byte offset from the beginning of a standard-layout type to specified member (function macro)
Defined in header <cstdbool>
__bool_true_false_are_defined (C++11)	C compatibility macro constant, expands to integer constant 1 (macro constant)
Defined in header <cstdalign>
__alignas_is_defined (C++11)	C compatibility macro constant, expands to integer constant 1 (macro constant)

Fixed width integer types (since C++11)

Numeric limits

Defined in header <limits>
numeric_limits	provides an interface to query properties of all fundamental numeric types. (class template)

C numeric limits interface

Runtime type identification

Defined in header <typeinfo>
type_info	contains some type's information, generated by the implementation. This is the class returned by the typeid operator. (class)
bad_typeid	exception that is thrown if an argument in a typeid expression is null (class)
bad_cast	exception that is thrown by an invalid dynamic_cast expression, i.e. a cast of reference type fails (class)
Defined in header <typeindex>
type_index (C++11)	wrapper around a type_info object, that can be used as index in associative and unordered associative containers (class)

Type traits (since C++11)

Type traits defines a compile-time template-based interface to query or modify the properties of types.

Attempting to specialize a template defined in the <type_traits> header results in undefined behavior, except that std::common_type may be specialized if the specialization depends on a user-defined type.

A template defined in the <type_traits> header may be instantiated with an incomplete type unless otherwise specified, notwithstanding the general prohibition against instantiating standard library templates with incomplete types.

Type properties

Defined in header <type_traits>
Primary type categories
is_void (C++11)	checks if a type is void (class template)
is_null_pointer (C++14)	checks if a type is std::nullptr_t (class template)
is_integral (C++11)	checks if a type is integral type (class template)
is_floating_point (C++11)	checks if a type is floating-point type (class template)
is_array (C++11)	checks if a type is an array type (class template)
is_enum (C++11)	checks if a type is an enumeration type (class template)
is_union (C++11)	checks if a type is an union type (class template)
is_class (C++11)	checks if a type is a non-union class type (class template)
is_function (C++11)	checks if a type is a function type (class template)
is_pointer (C++11)	checks if a type is a pointer type (class template)
is_lvalue_reference (C++11)	checks if a type is lvalue reference (class template)
is_rvalue_reference (C++11)	checks if a type is rvalue reference (class template)
is_member_object_pointer (C++11)	checks if a type is a pointer to a non-static member object (class template)
is_member_function_pointer (C++11)	checks if a type is a pointer to a non-static member function (class template)
Composite type categories
is_fundamental (C++11)	checks if a type is fundamental type (class template)
is_arithmetic (C++11)	checks if a type is arithmetic type (class template)
is_scalar (C++11)	checks if a type is scalar type (class template)
is_object (C++11)	checks if a type is object type (class template)
is_compound (C++11)	checks if a type is compound type (class template)
is_reference (C++11)	checks if a type is either lvalue reference or rvalue reference (class template)
is_member_pointer (C++11)	checks if a type is a pointer to a non-static member function or object (class template)
Type properties
is_const (C++11)	checks if a type is const-qualified (class template)
is_volatile (C++11)	checks if a type is volatile-qualified (class template)
is_trivial (C++11)	checks if a type is trivial (class template)
is_trivially_copyable (C++11)	checks if a type is trivially copyable (class template)
is_standard_layout (C++11)	checks if a type is standard-layout type (class template)
is_pod (C++11)	checks if a type is plain-old data (POD) type (class template)
is_literal_type (C++11)(deprecated in C++17)	checks if a type is literal type (class template)
has_unique_object_representations (C++17)	checks if every bit in the type's object representation contributes to its value (class template)
is_empty (C++11)	checks if a type is class (but not union) type and has no data (class template)
is_polymorphic (C++11)	checks if a type is polymorphic class type (class template)
is_final (C++14)	checks if a type is a final class type (class template)
is_abstract (C++11)	checks if a type is abstract class type (class template)
is_signed (C++11)	checks if a type is signed arithmetic type (class template)
is_unsigned (C++11)	checks if a type is unsigned arithmetic type (class template)

Supported operations
is_constructibleis_trivially_constructibleis_nothrow_constructible (C++11)(C++11)(C++11)	checks if a type has a constructor for specific arguments (class template)
is_default_constructibleis_trivially_default_constructibleis_nothrow_default_constructible (C++11)(C++11)(C++11)	checks if a type has a default constructor (class template)
is_copy_constructibleis_trivially_copy_constructibleis_nothrow_copy_constructible (C++11)(C++11)(C++11)	checks if a type has a copy constructor (class template)
is_move_constructibleis_trivially_move_constructibleis_nothrow_move_constructible (C++11)(C++11)(C++11)	checks if a type can be constructed from an rvalue reference (class template)
is_assignableis_trivially_assignableis_nothrow_assignable (C++11)(C++11)(C++11)	checks if a type has a assignment operator for a specific argument (class template)
is_copy_assignableis_trivially_copy_assignableis_nothrow_copy_assignable (C++11)(C++11)(C++11)	checks if a type has a copy assignment operator (class template)
is_move_assignableis_trivially_move_assignableis_nothrow_move_assignable (C++11)(C++11)(C++11)	checks if a type has a move assignment operator (class template)
is_destructibleis_trivially_destructibleis_nothrow_destructible (C++11)(C++11)(C++11)	checks if a type has a non-deleted destructor (class template)
has_virtual_destructor (C++11)	checks if a type has a virtual destructor (class template)
is_swappable_withis_swappableis_nothrow_swappable_withis_nothrow_swappable (C++17)(C++17)(C++17)(C++17)	checks if objects of a type can be swapped with objects of same or different type (class template)

Property queries
alignment_of (C++11)	obtains the type's alignment requirements (class template)
rank (C++11)	obtains the number of dimensions of an array type (class template)
extent (C++11)	obtains the size of an array type along a specified dimension (class template)

Type relationships
is_same (C++11)	checks if two types are the same (class template)
is_base_of (C++11)	checks if a type is derived from the other type (class template)
is_convertible (C++11)	checks if a type can be converted to the other type (class template)
is_callableis_nothrow_callable (C++17)	checks if a type can be invoked (as if by std::invoke) with the given argument types (class template)

Type modifications

Type modification templates create new type definitions by applying modifications on a template parameter. The resulting type can then be accessed through type member typedef.

Defined in header <type_traits>
Const-volatility specifiers
remove_cvremove_constremove_volatile (C++11)(C++11)(C++11)	removes const or/and volatile specifiers from the given type (class template)
add_cvadd_constadd_volatile (C++11)(C++11)(C++11)	adds const or/and volatile specifiers to the given type (class template)
References
remove_reference (C++11)	removes reference from the given type (class template)
add_lvalue_referenceadd_rvalue_reference (C++11)(C++11)	adds lvalue or rvalue reference to the given type (class template)
Pointers
remove_pointer (C++11)	removes pointer from the given type (class template)
add_pointer (C++11)	adds pointer to the given type (class template)
Sign modifiers
make_signed (C++11)	makes the given integral type signed (class template)
make_unsigned (C++11)	makes the given integral type unsigned (class template)
Arrays
remove_extent (C++11)	removes one extent from the given array type (class template)
remove_all_extents (C++11)	removes all extents from the given array type (class template)

Miscellaneous transformations

Defined in header <type_traits>
aligned_storage (C++11)	defines the type suitable for use as uninitialized storage for types of given size (class template)
aligned_union (C++11)	defines the type suitable for use as uninitialized storage for all given types (class template)
decay (C++11)	applies type transformations as when passing a function argument by value (class template)
enable_if (C++11)	hides a function overload or template specialization based on compile-time boolean (class template)
conditional (C++11)	chooses one type or another based on compile-type boolean (class template)
common_type (C++11)	deduces the result type of a mixed-mode arithmetic expression (class template)
underlying_type (C++11)	obtains the underlying integer type for a given enumeration type (class template)
result_of (C++11)	deduces the return type of a function call expression (class template)
void_t (C++17)	void variadic alias template (alias template)

Operations on traits

Defined in header <type_traits>
conjunction (C++17)	variadic logical AND metafunction (class template)
disjunction (C++17)	variadic logical OR metafunction (class template)
negation (C++17)	logical NOT metafunction (class template)

Helper classes

Defined in header <type_traits>
integral_constantbool_constant (C++11)(C++17)	compile-time constant of specified type with specified value (class template)

Two specializations of std::integral_constant for the type bool are provided:

Defined in header <type_traits>
Type	Definition
true_type	std::integral_constant<bool, true>
false_type	std::integral_constant<bool, false>

See also

C documentation for Type support library