redirecting output

[Eric Friets]

I need to redirect output in the middle of a program
from the standard output to a file.  The use of
fprintf is ruled out because I do not have the
source of the functions whose output I want.

Options that are not acceptable:
1. redirect output of the entire program, as in
	prog > file
2. have the rest of the program write to stderr, and 
then redirect the entire program, as above
3. write the necessary data to a file, and have a
smaller program that redirects to a file

What is really needed is a way to change the pointer
to stdout to a file pointer returned by fopen().  Any
suggestions would be appreciated.  I will summarize and
post responses that are mailed to me.

Eric Friets
emf at eleazar.dartmouth.edu
.