Re: unix epoch data wrapping

[sfeam (E. Merritt) <eam...@gm...>]

On Saturday 27 March 2010, pl...@pi... wrote:
> On 03/27/10 16:31, Jonathan Thornburg wrote:

> > 2-digit years are fundamentally ambiguous, so some (arbitrary) decision
> > must be made to resolve that ambiguity.  I'm not sure how gnuplot implements
> > this internally, but The X/Open standard documents a function  strptime()
> > whose man page on my computer says
> > |      %y    the year within the current century.  When a century is not other-
> > |            wise specified, values in the range 69-99 refer to years in the
> > |            twentieth century (1969 to 1999 inclusive); values in the range
> > |            00-68 refer to years in the twenty-first century (2000 to 2068 in-
> > |            clusive).  Leading zeros are permitted but not required.

From the gnuplot source file time.c:

        case 'y':               /* year number */
            s = read_int(s, 2, &tm->tm_year);
            /* In line with the current UNIX98 specification by
             * The Open Group and major Unix vendors,
             * two-digit years 69-99 refer to the 20th century, and
             * values in the range 00-68 refer to the 21st century.
             */
            if (tm->tm_year <= 68)
                tm->tm_year += 100;
            date++;
            tm->tm_year += 1900;
            break;