get number of files in archive
zip_get_num_entries() function returns the number of files in archive. If flags is set to
ZIP_FL_UNCHANGED, the original number of entries is returned.
zip_get_num_entries() returns the number of files in the zip archive, or -1 if archive is
zip_get_num_entries() was added in libzip 0.10. In libzip 0.11 the return type was changed from zip_uint64_t to zip_int64_t. In libzip 0.11 the type of flags was changed from int to zip_flags_t.