archive_version: Returns a text string, e.g., "libarchive 1.00.000"
archive_api_version: Returns the SHLIB major version
archive_api_feature: Returns a feature number useful for answering
questions such as "Is this recent enough to do XXX?"
The last two also have macros defined in archive.h, so you can compare
the compile-time and run-time environments. (In particular, you can
compare ARCHIVE_API_VERSION to archive_api_version() to detect library
version mismatches.)
With these in hand, it will soon be time to turn on the
shared-library version of libarchive... stay tuned.