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

constexpr std::size_t index() const noexcept;

(since C++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

#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

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

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

Example

See also