Quote Originally Posted by jamadagni
So you have evidently not understood what proleptic Gregorian is. It is not a separate calendar. "proleptic" is intended to mean "extended backwards".
So why do you distinguish between Gegorian calendar and proleptic Gregorian calendar if it is the same thing?

I guess that there should be something like a "local calendar" that would handle the transition from Julian to Gregorian calendar in locale-dependent manner.

Maybe instead altering Qt sources, that might cause problems when somebody mixes modified and original Qt libraries, you should design your own library that would provide more general date & time handling classes for Qt applications?