I/O redirection

William P. Kaufman wkaufman at oracle.oracle.com
Fri Apr 6 10:23:32 AEST 1990

In article <1990Apr2.144841.12905 at mentor.com> swhitchurch at mentor.com (Steve Whitchurch) writes:
>I have a question: I need to change or redirect "stdout" from inside
>a C function. What I want to do is capture the output of a printf and
>put the results into a file. so it would go something like this:
> redirect_stdout ();
> call_function_that_prints_to_stdout ();
> reset_stdout ();

Oooo, ugly.  There is a way, but it's thouroughly machine-depedent.  What you
can do is:
	freopen(file, "w", stdout);
	freopen("/dev/ttyXX", "w", stdout);
for a UNIX machine, assuming you know what terminal you're on,...or,...

Much easier is:
	FILE *out_fp = stdout;

	out_fp = fopen(new_file, "w");
	out_fp = stdout;
and change all your code from
	fprintf(out_fp, ...);
and put in some error checking.  _That's_ portable (modulo file-naming
conventions), you don't need to know your terminal, etc., etc.  Granted, it
won't work on procedures you can't control (say, perror()), but I hope it's
good enough for you.

Happy hunting,....
				-- Bill Kaufman

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