<type_traits>

Article
2015-07-29

Defines templates that provide compile-time constants that give information about the properties of their type arguments.

#include <type_traits>

Remarks

A type predicate is a template that takes one or two type arguments. When a type predicate holds true, it is publicly derived, directly or indirectly, from true_type Typedef. When a type predicate holds false, it is publicly derived, directly or indirectly, from false_type Typedef.

A type modifier is a template that takes one or more template arguments and has one member, as follows:

typedef modified-type type;

A type query is a template that takes one or more template arguments. A type query is publicly derived, directly or indirectly, from integral_constant<std::size_t, value>. It holds the value that is passed as the argument value.

Alias Templates

Alias templates for typename foo<T>::type are provided, where "foo" is the template class name. For example, add_const has the alias template for its type add_const_t, defined as:

template<class T>
    using add_const_t = typename add_const<T>::type;

add_const_t	aligned_storage_t	make_signed_t	remove_pointer_t
add_cv_t	aligned_union_t	make_unsigned_t	remove_reference_t
add_lvalue_reference_t	common_type_t	remove_all_extents_t	remove_volatile_t
add_pointer_t	conditional_t	remove_const_t	result_of_t
add_rvalue_reference_t	decay_t	remove_cv_t	underlying_type_t
add_volatile_t	enable_if_t	remove_extent_t

Classes

add_const	Makes const type from type.
add_cv	Makes const/volatile type from type.
add_pointer	Makes pointer to type from type.
add_reference	Makes reference to type from type.
add_volatile	Makes volatile type from type.
aligned_storage	Makes suitably aligned type.
alignment_of	Gets alignment of type.
common_type	Makes an instance of the common type of two types.
conditional	Makes an instance of the common type of two types.
decay	Makes non-reference, non-const, or non-volatile type, or makes a pointer to type.
enable_if	Makes an instance of a type, or an undefined type.
extent	Gets an array dimension.
has_nothrow_assign	Tests whether the type does not throw on assign.
has_nothrow_constructor	Tests whether the type does not throw on default construction.
has_nothrow_copy	Tests whether the type does not throw on copy construction.
has_nothrow_copy_constructor	Tests if type doesn't throw on copy construction.
has_nothrow_default_constructor	Tests if type doesn't throw on default construction.
has_trivial_assign	Tests whether the type has a trivial assign.
has_trivial_constructor	Tests whether the type has a trivial default constructor.
has_trivial_copy	Tests whether the type has a trivial copy constructor.
has_trivial_copy_constructor	Tests if type has a trivial copy constructor.
has_trivial_default_constructor	Tests if type has a trivial default constructor.
has_trivial_destructor	Tests whether the type has a trivial destructor.
has_virtual_destructor	Tests whether the type has a virtual destructor.
is_abstract	Tests whether the type is an abstract class.
is_arithmetic	Tests whether the type is arithmetic.
is_array	Tests whether the type is an array.
is_base_of	Tests whether one type is the base of another.
is_class	Tests whether the type is a class.
is_compound	Tests whether the type is not scalar.
is_const	Tests whether the type is const.
is_convertible	Tests whether one type is convertible to another.
is_empty	Tests whether the type is an empty class.
is_enum	Tests whether the type is an enumeration.
is_floating_point	Tests whether the type is floating-point.
is_function	Tests whether the type is a function type.
is_fundamental	Tests whether the type is void or arithmetic.
is_integral	Tests whether the type is integral.
is_lvalue_reference	Tests if type is an lvalue reference.
is_member_function_pointer	Tests whether the type is a pointer to a member function.
is_member_object_pointer	Tests whether the type is a pointer to a member object.
is_member_pointer	Tests whether the type is a pointer to a member.
is_object	Tests whether the type is an object type.
is_pod	Tests whether the type is a POD.
is_pointer	Tests whether the type is a pointer.
is_polymorphic	Tests whether the type has a virtual function.
is_reference	Tests whether the type is a reference.
is_rvalue_reference	Tests if type is an rvalue reference.
is_same	Tests whether two types are the same.
is_scalar	Tests whether the type is scalar.
is_signed	Tests whether the type is a signed integer.
is_standard_layout	Tests if type is a standard layout.
is_union	Tests whether the type is a union.
is_unsigned	Tests whether the type is an unsigned integer.
is_void	Tests whether the type is void.
is_volatile	Tests whether the type is volatile.
make_signed	Makes type or the smallest signed type greater than or equal in size to type.
make_unsigned	Makes type or the smallest unsigned type greater than or equal in size to type.
rank	Gets the number of array dimensions.
remove_all_extents	Makes non-array type from array type.
remove_const	Makes non-const type from type.
remove_cv	Makes non-const/volatile type from type.
remove_extent	Makes element type from array type.
remove_pointer	Makes type from a pointer to type.
remove_reference	Makes non-reference type from type.
remove_volatile	Makes non-volatile type from type.
integral_constant	Makes integral constant from type and value.

Typedefs

false_type	Holds integral constant with false value.
true_type	Holds integral constant with true value.

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<type_traits>

Remarks

Alias Templates

Classes

Typedefs

See Also

Reference

Additional resources