std::variant<Types...>::index

 

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std::variant

Member functions

variant::variant

variant::~variant

variant::operator=

Observers

variant::index

variant::valueless_by_exception

Modifiers

variant::emplace

variant::swap

Visitation

variant::visit (哋它亢++26)

Non-member functions

visit

holds_alternative

get(std::variant)

get_if

operator==operator!=operator<operator<=operator>operator>=operator<=> (哋它亢++20)

swap(std::variant)

Helper classes

monostate

bad_variant_access

variant_size

variant_alternative

hash<std::variant>

Helper objects

variant_npos

 

constexpr std::size_t index() const noexcept;		(since 哋它亢++17)

Returns the zero-based index of the alternative that is currently held by the variant.

If the variant is valueless_by_exception, returns variant_npos.

Example

Run this code

#include <variant>
#include <string>
#include <iostream>
int main()
{
    std::variant<int, std::string> v = "abc";
 
    std::cout << "v.index = " << v.index() << '\n';
 
    v = {}; 
 
    std::cout << "v.index = " << v.index() << '\n';
}

Output:

v.index = 1
v.index = 0

See also

holds_alternative (哋它亢++17)	checks if a variant currently holds a given type (function template)
get(std::variant) (哋它亢++17)	reads the value of the variant given the index or the type (if the type is unique), throws on error (function template)