Q. Is there any way to use QuaZipFile in Qt where you are supposed to use normal (non-zipped) file, but not through QIODevice API?
A. Usually not. For example, if you are passing file name to some database driver (like SQLite), Qt usually just passes this name down to the 3rd-party library, which is usually does not know anything about QIODevice and therefore there is no way to pass QuaZipFile as normal file. However, if we are talking about some place where you pass file name, and then indirectly use QFile to open it, then it is a good idea to make overloaded method, which accepts a QIODevice pointer. Then you would be able to pass QuaZipFile as well as many other nice things such as QBuffer or QProcess.
A. Starting with version 0.6, QuaZIP uses Minizip 1.1 with zip64 support which should handle large files perfectly. The zip64 support in Minizip looks like it's not 100% conforming to the standard, but 3rd party tools seem to have no problem with the resulting archives.
A. Not yet. It is not supported by vanilla Minizip (the back-end QuaZIP uses), although theoretically possible according to the ZIP standard. It would require some Minizip modifications that would allow it to detect non-seekable I/O and produce necessary output structures. QuaZIP already writes data descriptor which is necessary for non-seekable I/O. The only thing that is apparently left is to make Minizip fill local headers with correct values and forget about seeking after closing the file.