Fstream and stream operator << difference

Question

I want to overload the <<operator to serialize an object to a file (append). Which stream should I use? ofstreamor fstream? what is the difference?

std::ofstream& operator<<(std::ofstream& ofs, const MyData&);
std::fstream& operator<<(std::fstream& fs, const MyData&)

Thanks jack

Answer 1

You must overload the statement for ostream, then you can use it naturally for an instance of any class that comes from this: fromstream, fstream (inherits from iostream, which inherits both istream and ostream), ostringstream and stringstream (inherits iostream too)

std::ostream& operator<<(std::ostream& os, const MyData&);

Answer 2

std::ostream. , ? std::cout, .

iostreams . .

Answer 3

AFAIK, ofstream("file.txt") fstream("file.txt", ios::out).

Answer 4

, fstream. append-only, ofstream. , , ios::app.