[Boost-users] regex_replace to replace a specify string

Hi, Can someone please help? I would like to replace the match (*) with raw data. Is this possible? regex_replace(out, file_stream.begin(), file_stream.end(), my_regex, "(?12)", match_default | format_all); How can I replace the match with a number 2? I've tried difference combination of escape character before the 2 such as (?1\\d2) but it doesn't seems to work. Thanks, Mike