How to store dynamic data (unknown number of fields) to a file?

Question

I need to store some data in a file. FOR THE MOMENT each record (data set) consists in:

• a string (variable length),
• an array of integers (variable len

Answer 1

Use Synopse BigTable, http://synopse.info/ a key=>value database, value in this case is the serialization of you data (json, binary, xml, ...).

This is CRAZY fast, lightweight and free.