Conference vaxaxp::vmsnotes

I am a developer of a Web Server Extension program (ISAPI, NSAPI, & CGI) which
is being  delivered on OpenVMS, DIGITAL Unix, and Windows32.

As part of the functionality we need to send the current time to the Web
Browser in GMT format.

This is fine on Windows32 and DIGITAL Unix, as I can use the C Run Time
function gmtime.   However, this function does not work on OpenVMS.

So I started to look at SYS$GETUTC to return a UTC (or GMT by another name)
time.

However, the three other UTC calls, SYS$NUMUTC, SYS$ASCUTC, SYS$BINUTC seem to
insist that the date/time must be given/returned in local time.

So what I would like to do is interpret the 128 bit UTC time, and convert it
into a 'C'  tm structure,  so that I can write a function to  mimick the
behaviour of gmtime.

Are all the above statements true (on OpenVMS 6.2 upwards), and if so, could I
get some help with the UTC 128 bit date/time structure.

Thanks,

Steve

>>So what I would like to do is interpret the 128 bit UTC time, and convert it
>>into a 'C'  tm structure,  so that I can write a function to  mimick the
>>behaviour of gmtime.

I suggest you ask this question in turris::decc

gmtime is avaiable as of V6.1 of OpenVMS.  You don't mention what else is
missing or what version of OpenVMS is your target.

bjm

   This is more specifically a DEC C question, as was mentioned...

   The various UTC system services were added in OpenVMS V6.0.

   The OpenVMS version when a particular C RTL call was added is
   listed in the following table:

     http://hndymn.zko.dec.com/~crtl/when_functions_were_released.html

   You will want to avoid parsing the contents of the binary UTC format.
   (There doesn't seem to be a standard for the binary format of UTC --
   the UTC text formats are specified quite carefully, however.)

   Failing the availability of the DEC C RTL calls, I'd look at using
   sys$numutc, and/or the other RTL services -- see the "Time" chapter
   in the programming concepts manual for some information that may
   interest you.  (The LIB Run-Time Library (RTL) contains various 
   user-programmable date-time formatting routines, routines such as
   LIB$CONVERT_DATE_STRING.)

    re .0
    
    I recall someone else noticing the lack of support for other than local
    time zone. (That person was also threatening carnal knowledge of the
    128-bit format and my recollection is that the recommendation was "Just
    say 'No'".) I suggest that you look in old versions of VMSNOTES.

    Re: .0
    
    If the OpenVMS node has DECnet-Plus installed, then you could just call
    utc_ascgmtime()   [see the DECnet-Plus DECdts Programming manual]
    
    John.

  I think, "real" gmtime() function, returning a pointer to a tm structure
  which contains broken-down time expressed as UTC, became avaiable beginning
  with OpenVMS V7.0. Prior to V7.0, this function always returns a NULL
  pointer.

  On OpenVMS 6.0, 6.1 and 6.2 you can use exec-mode SYS$TIMEZONE_DIFFERENTIAL
  logical from LNM$SYSTEM_TABLE table to calculate UTC. This logical is set to
  contain the time differentiate factor (TDF) which is the difference in
  seconds between the local system time and UTC.

  To mimick the behaviour of gmtime() on V6.?, you can do the following:

	. translate SYS$TIMEZONE_DIFFERENTIAL logical

	. call the time() function and subtract from the returned value the
	  value of SYS$TIMEZONE_DIFFERENTIAL. The result will present the
	  number of seconds since Epoch for UTC

	. pass the result to the localtime() function to obtain broken-down
	  time in the form of the tm structure. The result will be as if the
	  gmtime() was called for the original returned value of the time()
	  function

  Boris

Example
=======

(LNM$SYSTEM_TABLE)	[kernel]  [shareable,system]
			[Protection=(RWC,RWC,R,R)]  [Owner=[SYSTEM]]

  "SYS$TIMEZONE_DIFFERENTIAL" [exec] = "-18000"

#include <stdio.h>
#include <time.h>

#define TDF (-18000)

static void display_tm(struct tm *tm_ptr);

main()
{
    time_t timer;
    struct tm *tm_ptr;

    timer = time(NULL);

    tm_ptr = localtime(&timer);
    printf("\nLocal Time:\n");
    display_tm(tm_ptr);

    timer -= TDF;
    tm_ptr = localtime(&timer);
    printf("\nGMT:\n");
    display_tm(tm_ptr);
}
static void display_tm(struct tm *tm_ptr)
{
    printf("tm_ptr->tm_sec  = %d\n", tm_ptr->tm_sec );
    printf("tm_ptr->tm_min  = %d\n", tm_ptr->tm_min );
    printf("tm_ptr->tm_hour = %d\n", tm_ptr->tm_hour);
    printf("tm_ptr->tm_mday = %d\n", tm_ptr->tm_mday);
    printf("tm_ptr->tm_mon  = %d\n", tm_ptr->tm_mon );
    printf("tm_ptr->tm_year = %d\n", tm_ptr->tm_year);
    printf("tm_ptr->tm_wday = %d\n", tm_ptr->tm_wday);
    printf("tm_ptr->tm_yday = %d\n", tm_ptr->tm_yday);
}

Local Time:
tm_ptr->tm_sec  = 27
tm_ptr->tm_min  = 33
tm_ptr->tm_hour = 8	<<<<<<<<<<<<<<
tm_ptr->tm_mday = 30
tm_ptr->tm_mon  = 0
tm_ptr->tm_year = 97
tm_ptr->tm_wday = 4
tm_ptr->tm_yday = 29

GMT:
tm_ptr->tm_sec  = 27
tm_ptr->tm_min  = 33
tm_ptr->tm_hour = 13	<<<<<<<<<<<<<<
tm_ptr->tm_mday = 30
tm_ptr->tm_mon  = 0
tm_ptr->tm_year = 97
tm_ptr->tm_wday = 4
tm_ptr->tm_yday = 29

re .6
    
>	. call the time() function and subtract from the returned value the
>	  value of SYS$TIMEZONE_DIFFERENTIAL.
    
    How does this logical name get set? On both my systems it is -46800
    which looks invalid to me.
    
    P.S. For quick hacks
    
    int tdf = atoi(getenv("SYS$TIMEZONE_DIFFERENTIAL"));

:>	. call the time() function and subtract from the returned value the
:>	  value of SYS$TIMEZONE_DIFFERENTIAL.
:    
:    How does this logical name get set?

   One can set and show it with SYS$MANAGER:UTC$CONFIGURE_TDF.COM

:    On both my systems it is -46800 which looks invalid to me.

   Where (when? :-) are you?  The TDF value is in seconds, relative
   to GMT.

    -46800 is the value used when the timezone has not been set up.  It's
    equivalent to -13:00.
    
    				Steve