std::variant<Types...>::index (3) - Linux Manuals

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

NAME

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

Synopsis

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

// 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