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HP OpenVMS Systemsask the wizard |
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The Question is: How can I generate a weeknumber? Is this by using the lexical function f$time or f$cvtime? The Answer is :
By week number, the OpenVMS Wizard will assume you mean the week within
the year, and specifically a value between 1 and 52 inclusive. As there
are various accepted definitions for a week number, there is no single
DCL lexical function or argument that can retrieve the desired.
Given that there are only 52 weeks in a year, and given that DCL is not
particularly suited for date arithmetic, and given that computers are
fast, the simplest way to is to count the week.
For example, assuming that week 1 starts on 1-Jan and week 2 starts on
8-Jan (etc...), this procedure uses combination times to count backwards
in multiples of 7 to find the first day not in the current year, at the
same time as counting up weeks.
$ day=F$CVTIME(p1,"ABSOLUTE","DATE")
$ weeknum=0
$ offset=0
$ year=F$CVTIME(day,,"YEAR")
$ loop:
$ weeknum=weeknum+1
$ offset=offset+7
$ IF F$CVTIME("''day'-''offset'-0",,"YEAR").EQS.Year THEN GOTO loop
$ WRITE SYS$OUTPUT weeknum
$ EXIT
Minor variations can be made to this procedure to accomodate other
definitions for week number.
Remember that in the worst case, the above procedure will loop for 53
iterations, so unless your code is highly performance sensitive, it
shouldn't be a problem. If your code is performance sensitive, please
create and code an algorthm using a compiled language.
Within a compiled language, you can generate the weeknumber for any
given date. For example, you can generate the week number for any
given date using the strftime() C Run-time library function, and
specifically the %W directive. This will give you a week number in
the range [00,53], where Monday is the first day of the week. For
the purposes of this C example, all days in the year preceding the
first Monday are considered to be in week 0.
For example, for current date:
$ run x
$ Monday May 06 2002 is in week number 18
$
x.c
---
#include <time.h>
#include <stdio.h>
main() {
char s[80];
time_t t = time(NULL);
struct tm *tms = localtime(&t);
strftime(s, sizeof(s), "%A %B %d %Y is in week number %W", tms);
puts(s);
}
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