std::variant_alternative, std::variant_alternative_t

 

C++

Language

Standard library headers

Concepts

Utilities library

Strings library

Containers library

Algorithms library

Iterators library

Numerics library

Input/output library

Localizations library

Regular expressions library (C++11)

Atomic operations library (C++11)

Thread support library (C++11)

Filesystem library (C++17)

Technical Specifications

 

Utilities library

Type support (basic types, RTTI, type traits)

Dynamic memory management

Error handling

Program utilities

Variadic functions

Date and time

Function objects

initializer_list (C++11)

bitset

hash (C++11)

Relational operators

rel_ops::operator!=rel_ops::operator>rel_ops::operator<=rel_ops::operator>=

optional, any and variant (C++17)

optional

any

variant

in_placein_place_typein_place_indexin_place_tin_place_type_tin_place_index_t

Pairs and tuples

pair

tuple (C++11)

apply (C++17)

make_from_tuple (C++17)

piecewise_construct_t (C++11)

piecewise_construct (C++11)

integer_sequence (C++14)

Swap, forward and move

swap

exchange (C++14)

forward (C++11)

move (C++11)

move_if_noexcept (C++11)

Elementary string conversions

to_chars (C++17)

from_chars (C++17)

chars_format (C++17)

Type operations

declval (C++11)

as_const (C++17)

 

std::variant

Member functions

variant::variant

variant::~variant

variant::operator=

Observers

variant::index

variant::valueless_by_exception

Modifiers

variant::emplace

variant::swap

Non-member functions

visit

holds_alternative

get

get_if

operator==operator!=operator<operator<=operator>operator>=

swap

Helper classes

monostate

bad_variant_access

variant_size

variant_alternative

hash

uses_allocator

Helper objects

variant_npos

 

Defined in header <variant>
template <std::size_t I, class T> struct variant_alternative; /* undefined */	(1)	(since C++17)
template <size_t I, class... Types> struct variant_alternative<I, variant<Types...>>;	(2)	(since C++17)
template <size_t I, class T> class variant_alternative<I, const T>; template <size_t I, class T> class variant_alternative<I, volatile T>; template <size_t I, class T> class variant_alternative<I, const volatile T>;	(3)	(since C++17)

Provides compile-time indexed access to the types of the alternatives of the possibly cv-qualified variant, combining cv-qualifications of the variant (if any) with the cv-qualifications of the alternative.

Formally,

2) meets the TransformationTrait requirements with a member typedef type equal to the type of the alternative with index I

3) meets the TransformationTrait requirements with a member typedef type that names, respectively, std::add_const_t<std::variant_alternative<I,T>>, std::add_volatile_t<std::variant_alternative<I,T>>, and std::add_cv_t<std::variant_alternative<I,T>>

Member types

Member type	Definition
type	the type of Ith alternative of the variant, where I must be in [0, sizeof...(Types)), otherwise the behavior is undefined

Helper template alias

template <size_t I, class T> using variant_alternative_t = typename variant_alternative<I, T>::type;		(since C++17)

See also

variant_sizevariant_size_v (C++17)	obtains the size of the variant's list of alternatives at compile time (class template) (variable template)
tuple_element	obtains the type of the specified element (class template specialization)