There is no method in quickfix to parse the message in human readable format. Another option is when you handle an incoming FIX message in onMessage, you would anyway parse it to read the message. Here you can list down the tagname and values to a file or DB. But any operation to do so may slow down your Quickfix engine, because writing to a file or DB is always slow. So BEWARE !!
Another option is log your messages to your DB instead of a file and then do all your stuff in the DB, but that would mean parsing a message twice i.e. in your engine and DB. But you would get a lot more flexibilty about what you want to read and what not to.