do not use off_t in headers - largefile sensitivity bugs!
Through a discussion on alt.os.linux.mandrake, I had to notice that every library has a risk of being broken when using the system off_t type in its exported interfaces, including structures and function synopsis.
The point comes from the fact that systems like linux and solaris are "largefile sensitive" - a -D_LARGEFILE_SOURCE will shift the "off_t" type from being a 32bit entity into a 64bit entity. This will make for a nice and pretty callframe mismatch.
A autoconf'ed lib 'centric treatment of the topic is given in:
Grepping a bit through files on my system, I did notice that even zlib/gzip is affected (and only by luck it is not triggered) and kdelib header files (in kio) has off_t as well. Bug reports were filed to the respective projects.
People should worry and learn about this problem area sooner than later