Hello udunits people,
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?
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) dpierce@xxxxxxxx
-------------------------------------------------------------------
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);
}
