How to "parametrize" an output stream?

Question

How can I make this pseudo-code work?

std::ostream  ostr;
std::ofstream ofstr;

if(condition) {
    ostr = std::cout;
}
else {
    ofstr.open("file.txt");
    ostr = ofstr;
}

ostr << "Hello" << std::endl;

This does not compile, since std::ostream does not have a public default constructor.

Answer 1

In your case you may use ternary operator:

std::ostream& ostr = (condition ?
                      std::cout :
                      (ofstr.open("file.txt"), ofstr)); // Comma operator also used
                                                        // To allow fstream initialization.