Is cin a proper file object?

Question

As in, can I pass cin to any function that accepts an ifstream object?

Answer 1

std::cin is not a file stream, but an input stream, or istream. You can pass it to any function that accepts an istream.

Answer 2

std::cin is a std::istream.

There is little difference between class istream and its derivative ifstream. ifstream allows you to open and close files, providing open(), close(), and is_open(), and a constructor which calls open() — and that's it!

If your function doesn't use those methods, it should take an istream& instead of an ifstream&.