How to override cout in C++?

Question

I have a requirement, I need to use printf and cout to display the data into console and file as well. For printf I have

Answer 1

If i guess correctly you want to log everything that goes to the output also into a file.

What you want is an observer pattern.

Replace all direct logging in your code with calls to a new relay. The logging relay sends your messages to the observers. One of your observers loggs the message to the screen. The other one loggs to the file. Avoid making your relay a singleton if possible.

This suggestion only works if you can edit all of your source files.