New to Jitter~ how to write a file in jitter?

Hi, Im a master student just starting work on a project using Jitter. I have my C++ codes already, which are used to compress images and put them in the form of raw data and save them to a text file. Now Im trying to convert my complicated c++ codes to jitter style in order to implement this compression algorithm with a jitter-external object
The problem I encounted here is how to write compressed raw data to a text file and save it as a text file under some directory? Is it possible to do write and save in a jitter object? I tested on the source codes of an existing jitter-external object, with inserting some command lines including fopen, fprintf, and fclose, but it didn't generate any file after build...>_<
Does any one know or has an example about how to write and save in jitter? Or is there any existing jitter object do similar things?
Any advice would be very appreciated~~~>_<