fprintf

• Use fprintf(FILE *, char *format, ...) to write to files. It works just like printf or sprintf -- in fact, all printf usually does is call fprintf( stdout, ... ).

• The three files stdin, stdout, and stderr are predefined for you in stdio.h. By default, stdin is the keyboard, and stdout and stderr are both the console monitor.

• It is a good idea to write error messages to stderr and not to stdout. Why? Because programs frequently have their standard output redirected to another file or program. If you cat foobar > mojo and their is an error opening foobar, then you want to hear about it on the console, not in mojo.

• You can't write to files opened for only reading (like stdin) or read from files opened only for writing (like stderr or stdout).