如何临时使用 std::cout 代替 std::ofstream

Question

if I want to create a logging class, say

class logging_class {
public:
    std::ofstream error;
    std::ofstream event;
    logging_class() {}
    logging_class(string err, string evt) {
        error.open(err);
        event.open(evt);
    }
    ~logging_class() {
        error.close();
        event.close();
    }
};

so that later I can easily create program log:

logging_class logger("Log_Error.txt","Log_Event.txt");
logger.error << "something wrong";
logger.event << "something interesting";

Now, at the early stage of development, I want to redirect all the output to screen (ie std::cout). I don't want to change the usage of logger.error<<"something wrong";to std::cout<<"something wrong"; , because later I will need to change all instances of std::cout to either logger.error or logger.event (maybe thousands of them). Can I make some easy changes in the class logger to do this?

Update: Following Enlico's instruction, I can modify the logging_class as:

class logging_class {
public:
    //std::ofstream error;
    //std::ofstream event;
    std::ostream& error;
    std::ostream& event;
    logging_class():error(std::cout),event(std::cout) {}
    //logging_class(string err, string evt) {
    //    error.open(err);
    //    event.open(evt);
    //}
    //~logging_class() {
    //    error.close();
    //    event.close();
    //}
};

and after creating object with default constructor: logging_class logger; I can now redirect all the logging to screen display.

Answer 1

Think of std::cout of what it actually is: an object. It is just that:

The global objects std::cout and std::wcout control output to […]

So when you say that you want to temporarily use std::cout in place of std::ofstream you're mixing apples (object std::cout ) with oranges (class std::ofstream ).

What you want to do, instead, is to use std::cout instead of an object of class std::ofstream .

But std::cout is not of class std::ofstream , so error can't hold it; it is of class std::ostream , which is a superclass of the former.

Therefore, as suggested in a comment, you can make error / event references to an object of that class, std::ofstream std::ostream& , and initialize them with std::cout or with std::ofstream{"filename.txt"} via an appropriate constructor of the logging_class .