Getting control of std. streams in gcc

Question

How can I get control of the stdin, stdout and stderr streams in gcc.??

We can redirect the error and output to separate files for sure, but is there a way that i can control the stdin such that whenever my program is executing and there is a moment when the stdin waits for a input(either from the user keyboard or any file), it sets a signal / changes the value of a variable or something like that so that i can get to know that now the stdin is waiting for the input, so that i can proceed accordingly and do something (e.g.show user a message or anything)

The other way i can think of doing it is continously polling the stdin stream somehow and whenever it waits for input, do my action. But again I don't know how to do this.?

Let me know if the question is not clear enough.

Answer 1

The simplest way I can think of, is to split "your program" into two. One reads from stdin as it is doing now. The other spawns the first program with its stdin connected to a pseudoterminal. Whenever the first program blocks waiting for input, then, the second program will unblock from waiting for output to the pseudoterminal. (You want a pseudoterminal rather than a pipe to avoid buffering headaches.)

There doesn't seem to be a good online explication of how to do this, but W. Richard Stevens' Advanced Programming in the UNIX Environment covers it quite well.