Create a print function that takes an ostream as an argument and writes to that stream

Im currently anwsering exercise questions concerning opera开发者_高级运维tor overloading in C++. I have a question:

Create a simple class containing an int and overload the operator+ as a member function. Also provide a print( ) member function that takes an ostream& as an argument and prints to that ostream&. Test your class to show that it works correctly.

I can create the class and write the operator+ function alright but I really dont understand the second part of the question. So far in my study of c++ I havent really come across ostream's and as such am not sure if its possible to explicitly create such a stream. I have tried using:

std::ostream o;

However this produces an error. Could someone please enlighten me on how I should create this function please?

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So far in my study of c++ I havent really come across ostream's and as such am not sure if its possible to explicitly create such a stream. I have tried using: std::ostream o;

You must have missed something, because ostreams are important. std::cout is a variable of type std::ostream by the way. Usage is more or less like this

#include <iostream> //defines "std::ostream", and creates "std::ofstream std::cout"
#include <fstream> //defines "std::ofstream" (a type of std::ostream)
std::ostream& doStuffWithStream(std::ostream &out) { //defines a function
    out << "apples!";
    return out;
}
int main() {
    std::cout << "starting!\n"; 
    doStuffWithStream(std::cout); //uses the function

    std::ofstream fileout("C:/myfile.txt"); //creates a "std::ofstream"
    doStuffWithStream(fileout); //uses the function

    return 0;
}

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You don't create an ostream, you create an ostream reference, like your exercise question said. And you do it in the parameter list of your print function, i.e.

void print(std::ostream & os);

Then you can call that function, passing cout or any other object of a class derived from ostream(ofstream, ostringstream, etc...)