Difference between fstream, ofstream, ostream, iostream

Question

I'm taking a quiz on an intro level class in C++ and I'm trying to understand a question. After searching the internet and not getting an answer, so here I am.

Which of the following function declarations will accept either cout or a file stream 
object as its argument?

A. void output( fstream &outFile);  
B. void output( ofstream &outFile); 
C. void output( ostream &outFile);  
D. void output( iostream &outFile);

The answer is C.

I know the difference between: fstream, ofstream, ostream, iostream.

What I don't understand is why none of the other options are able to accept the cout or file stream object as an argument.

Is the answer as simple as ostream objects contain data (char,etc) that are able to be passed as arguments?

Any information would be greatly appreciated.

Maestro

Perhaps this C++ I/O reference and its inheritance hierarchy diagram can help? – Hardboard

Related: Is it possible to pass derived classes by reference to a function taking base class as a parameter – Oddity

I would choose D because a file stream can be input and output. Answer C is output only. – Galicia

@ThomasMatthews: D doesn't work because you can't pass std::cout to it; it's not an std::istream. – Uzzia

If I have an ifstream for reading, which is a file stream, I can't use C. The question should be reworded. :-) – Galicia

@ThomasMatthews The function is called output. How confusing would that be if it read from a file? – Oddity

Answer 1

The answer is C. The question is about the inheritance hierarchy. std::cout is an instance of std::ostream. All other functions accept subclasses of std::ostream and can therefore not handle std::cout. std::fstream could be passed to all of them but the question was about both.

Parhe