regex_replace with file streams

Hi, I am new to the boost library, STL and template programming.. I want to use regex_replace to operate on a potentially large input file and output the results to another file. So, I can't load the entire file into a buffer in memory and pass it in as is done in the examples. I can't seem to figure out how to pass fstream or some other file I/O into regex_replace (ie create the proper iterator). Any help would be greatly appreciated. Louis