< cpp‎ | utility‎ | variant
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.


#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';


v.index = 1
v.index = 0

See also

checks if a variant currently holds a given type
(function template)
reads the value of the variant given the index or the type (if the type is unique), throws on error
(function template)