Re: Storage of Null Informix dates

On Tue, 25 Nov 1997, Guy Smithson wrote: > Does anyone know how NULL/Blank Informix dates are stored. Yes, I do. > I have a sample data file and the 4 byte integer containing a NULL > Informix-Date has it's highest bit set to one (0x80000000). And so do you. > Is this always the case, Yes. > or do other storage formats for NULL/Blank Informix-Dates exist also > (like 0x00000000) ? 0x00000000 is a perfectly good non-null date; 31st December 1899 to be precise. Dates are stored as the number of days since 31st December 1899, so day 1 is 1st January 1900 (which was not a leap year!). Null dates are stored as if they were null integers, which means as 0x80000000. On machines which use 32-bit twos-complement arithmetic, this number can be negated, but produces the same value. You might have noticed that the range of SMALLINT values is documented as -32767..+32767; the missing value (-32768 or 0x8000) is deliberately omitted because it is used to represent NULL. Similarly for INTEGER and SERIAL and DATE... Yours, Jonathan Leffler (johnl@informix.com) #include <witticism.h>