homemade file formats will bring more complication : you'll have to craft a routine to translate ASCII or binary data to program-readable data. This is achieved by operating with QIODevice(s) such as QTextStream and the on the data the read in file, either line by line or everything at the same time.

If you're curious enough have a look at the project parser in DevQt : converts a *.pro into a complex data structures that take care of scopes, variables and operators.