[Support #LXO-177503]: [udunits] Behavior of ut_decode_time depends on call order?

David,

[I moved your email into our support-system.]

> I've encountered what is, to me, surprising behavior in routine
> "ut_decode_time", and I'm wondering if it's a bug or a feature. :)
> 
> Specifically, the results returned seem to depend on the order of calls to
> other, not-obviously-related udunits-2 routines.  For example, the use of
> the ut_decode_time routine is supposed to be related to "encoding [time]
> as a double-precision value, which can then be acted upon arithmetically"
> (from the udunits-2 docs).  Which would suggest that the values to be
> acted upon arithmetically shouldn't have different interpretations
> depending on call order. But on my system at least, it (schematically)
> does this:
> 
> timeval = whatever
> ut_decode_time( timeval, etc) gives Date #1
> ...
> ut_decode_time( timeval, etc) gives Date #1 again, as you expect
> 
> -but-
> 
> timeval = whatever
> ut_decode_time( timeval, etc) gives Date #1
> ...
> ut_parse( "days since some origin time" )
> ...
> ut_decode_time( timeval, etc) gives a *different* date, as you don't expect
> 
> 
> Minimal example code is appended below that shows this.  The output on my
> system (omitting the "definition overrides" warnings) is:
> 
> decoding time location A: tval=0.000000  -4713/1/1 0:0:00.000
> decoding time location A-2: tval=0.000000  -4713/1/1 0:0:00.000
> decoding time location B: tval=0.000000  2001/1/1 0:0 0.000000
> 
> Is this expected behavior?

Congratulations!  You've uncovered a bug in the initialization of the core 
module of the UDUNITS-2 package.

I'm making a new release as I write this.  I'll let you know when it's 
available.

> Regards,
> 
> --Dave
> 
> -------------------------------------------------------------------
> David W. Pierce
> Division of Climate, Atmospheric Science, and Physical Oceanography
> Scripps Institution of Oceanography
> (858) 534-8276 (voice)  /  (858) 534-8561 (fax)    address@hidden
> -------------------------------------------------------------------
> 
> code example:
> 
> #include <stdio.h>
> #include <udunits2.h>
> #include <stdlib.h>
> 
> #define BUFLEN 1024
> 
> /*===========================================================================================================*/
> int main( int argc, char *argv[] )
> {
> int     year, month, day, hour, minute;
> double  second, resolution;
> double  tval;
> ut_system *unitSystem;
> ut_unit   *utu1;
> 
> /* Initialize unit system */
> unitSystem = ut_read_xml(NULL);
> if( unitSystem == NULL ) {
> fprintf( stderr, "error initializing unit system\n" );
> exit(-1);
> }
> 
> /* Decode a time value of 0, print its date */
> tval = 0.0;
> ut_decode_time( tval, &year, &month, &day, &hour, &minute,
> &second, &resolution );
> printf( "decoding time location A: tval=%lf  %d/%d/%d
> %d:%d:%06.3lf\n",
> tval, year, month, day, hour, minute, second );
> 
> /* Repeat just to make sure */
> ut_decode_time( tval, &year, &month, &day, &hour, &minute,
> &second, &resolution );
> printf( "decoding time location A-2: tval=%lf  %d/%d/%d
> %d:%d:%06.3lf\n",
> tval, year, month, day, hour, minute, second );
> 
> /* Parse a timestamp string */
> utu1 = ut_parse( unitSystem, "days since 2010-01-08 11:44",
> UT_ASCII );
> if( utu1 == NULL ) {
> fprintf( stderr, "Error parsing unit string with current
> date\n" );
> exit(-1);
> }
> 
> /* Repeat decoding a time value of 0, print its date */
> tval = 0.0;
> ut_decode_time( tval, &year, &month, &day, &hour, &minute,
> &second, &resolution );
> printf( "decoding time location B: tval=%lf  %d/%d/%d %d:%d %lf\n",
> tval, year, month, day, hour, minute, second );
> 
> return(0);
> }

Regards,
Steve Emmerson

Ticket Details
===================
Ticket ID: LXO-177503
Department: Support UDUNITS
Priority: Normal
Status: Open