SQLite Forum

Subclassing & private data
> Actually, no. I'm wondering how do I write my code as to be forward compatible with future versions of Sqlite that may add new members to the structs without breaking my code written for the current versions.

If the SQLite library were to change the definition of the leading (or not yet "subclassed") portion of the structs it uses at the extension interfaces, it would break a great many extensions compiled against earlier versions of that publicly exposed data. This kind of backward incompatibility is carefully avoided by the project's management and the developers generally.

> As I mentioned in my OP, C is not my forte and from what I saw so far, C has the convention of having a field in a struct to report the size of the structure or in Sqlite's case, the version supported. 

Neither of those common practices is a C convention. You accurately perceive what the practice accomplishes. If the library designer(s) had elected to leave room for later, changed versions of those structs, a member named something like sizeof_public_portion might well have been used. However, along with such changed data structure would come changed requirements as to what is done with it or perhaps changed allowance as to what the extension might do with it. Those intriguing options for change are closed off by the API stability guarantees that are part of the library's interface.

> How will I know that I won't be writing code that will break in a future version of Sqlite?

The same way that you know sqlite3_open() will do the same thing next decade as it does today.