typedef void (*zip_progress_callback)(zip_t *, double, void *);
(*ud_free)(void *), void
zip_register_progress_callback_with_state() function registers a callback function callback for the zip archive archive. The precision argument is a double in the range from 0.00 to 1.0 that defines the smallest change for which the callback should be called (to avoid too frequent calls). The ud_free function is called during cleanup for deleting the userdata supplied in ud.
The callback function is called during zip_close(3) in regular intervals (after every zip archive entry that's completely written to disk, and while writing data for entries) with zip archive archive, the current progression state as a double, and the user-provided user-data ud as arguments. The progression state is a double in the range from 0.0 to 1.0. This can be used to provide progress indicators for user interfaces.
zip_register_progress_callback_with_state() was added in libzip 1.3.0.