Path: utzoo!attcan!uunet!jarthur!usc!apple!oracle!news
From: wkaufman@oracle.oracle.com (William P. Kaufman)
Newsgroups: comp.lang.c
Subject: Re: I/O redirection
Message-ID: <1990Apr6.002332.8371@oracle.com>
Date: 6 Apr 90 00:23:32 GMT
References: <1990Apr2.144841.12905@mentor.com>
Reply-To: wkaufman@oracle.com (William P. Kaufman)
Organization: Oracle Corporation, Belmont CA
Lines: 36

In article <1990Apr2.144841.12905@mentor.com> swhitchurch@mentor.com (Steve Whitchurch) writes:
>Hi;
>
>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);
	function..();
	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");
	call_function_that_prints_to_out_fp();
	out_fp = stdout;
and change all your code from
	printf(...);
ro
	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