gwalker@BBN-SPCA.ARPA (Gail Rubin Walker) (07/01/86)
If I want to compute a date (VAX quadword date form) that is 1 month from today - what is the best way? It seems to me that there is a system service 'missing'. I can get the current date/time in a 7-word array with sys$numtim. One of the words is month number. I can add 1 to that (and do the appropriate things if I've gone off the end of the year) but then what? There doesn't appear to be a service that converts from the 7 word array back to the vax quadword format. Or even from the 7 word array to an ascii string. The other system services that deal with quadword times convert from quadword to ascii string and back - that doesn't help. Do I really have to then myself turn the 7 word array into an ascii string to use sys$bintim to get back to the quadword form? Or have I just overlooked a system routine somewhere? -- Gail Walker gwalker@bbn-spca
LEICHTER-JERRY@YALE.ARPA.UUCP (07/03/86)
If I want to compute a date (VAX quadword date form) that is 1 month from
today - what is the best way?
The quadword format is the one to work with; since it is a simple binary
number - yes, I know it's a quadword - you can do arithmetic on it:
a) Use $GETTIM to get the current time into quadword NOW.
b) Now you need, in quadword DELTA, a delta time that represents
"one month". Unfortunately, there is no notation for "plus
one month" - only for "plus some number of days". So you'll
need to compute the number of days in the current month ("30
days hath September, all the rest I don't remember", to quote
Martin Minow) - call it dd - and convert the delta time
"dd 00:00:00.00" into DELTA, again with $BINTIM.
c) The value you want is NOW - DELTA. (It's "-" rather than "+"
because delta times in quadword format are stored negated.)
That leaves the problem of doing quadword arithmetic, something no HLL does
directly. However, there is a library procedure - LIB$SUBX - to do exactly
that. The quadword values themselves your HLL program will consider to be
arrays of 2 longwords.
There is an alternative approach: Rather than using $NUMTIM, use $ASCTIM.
The ASCII string you get back isn't nearly as convenient for manipulation as
the array $NUMTIM gives you, but you CAN convert it back with $BINTIM.
-- Jerry
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