I'm switching over some of my numerical models to use netCDF because it's
quite a nice system (i.e., thanks for making it available!). I do have a
couple of comments, though. Specifically, I think the choice to have netCDF
change the *variable ids* depending on whether the package is called from a
C program or a FORTRAN program is a mistake. There is no reason why the
user should ever do anything with those ids besides pass them, unmodified,
back to other netCDF routines. Having to add or subtract 1 from values which
should never be altered, depending on which language you call the package
from, seems like a mistake to me. Just to be specific, I've included a
script of the output from a C/FORTRAN combination which shows what, in my
opinion anyway, is very undesirable behavior:
*** opencdf.c: ***
#include "/usr/local/include/netcdf.h"
long
opencdf_( varid )
long *varid;
{
long cdfid;
long dims[1];
long dim_x, dim_y, dim_z, var_x, var_y, var_z;
char *message_x="this is X", *message_y = "this is Y",
*message_z="this is Z";
char *title = "title for the test cdf file";
cdfid = nccreate( "test.cdf", NC_CLOBBER );
dim_x = ncdimdef( cdfid, "dim_x", 10L );
dim_y = ncdimdef( cdfid, "dim_y", 15L );
dim_z = ncdimdef( cdfid, "dim_z", 20L );
dims[0] = dim_x;
var_x = ncvardef( cdfid, "var_x", NC_FLOAT, 1, dims );
dims[0] = dim_y;
var_y = ncvardef( cdfid, "var_y", NC_FLOAT, 1, dims );
dims[0] = dim_z;
var_z = ncvardef( cdfid, "var_z", NC_FLOAT, 1, dims );
ncattput( cdfid, NC_GLOBAL, "title", NC_CHAR,
strlen(title)+1, title );
ncattput( cdfid, var_x, "message", NC_CHAR,
strlen(message_x)+1, message_x );
ncattput( cdfid, var_y, "message", NC_CHAR,
strlen(message_y)+1, message_y );
ncattput( cdfid, var_z, "message", NC_CHAR,
strlen(message_z)+1, message_z );
ncendef( cdfid );
ncsync ( cdfid );
/* Return the Y variable, so message should be "this is Y" */
*varid = var_y;
return( cdfid );
}
*** t.f ***
program test
character*60 attribute
character*60 title
icdf = opencdf( iyid )
c ------------------------------------------------------
c Note: if you comment the following two lines out, the
c next NCAGTC call barfs! Why?
c ------------------------------------------------------
call ncainq( icdf, NCGLOBAL, 'title', itype, ilen, ierr )
print *, 'title type, length:',itype,ilen
call ncagtc( icdf, NCGLOBAL, 'title', title, ilen, ierr )
call ncagtc( icdf, iyid, 'message', attribute, ilen, ierr )
c This should print out "this is Y"
print *, attribute
end
Script started on Wed Oct 21 14:09:19 1992
(killer)1> cc -c opencdf.c
(killer)2> f77 -o test opencdf.o t.f -lnetcdf
(killer)3> test
title type, length: 2 28
this is X
(killer)4> ^D
script done on Wed Oct 21 14:09:45 1992
Although the y variable id is returned, when this exact same value is
used from FORTRAN, a different variable is accessed! I haven't checked
whether this is true for dimension ids also. At the very least, having
a +/- 1 difference in the *variable* ids when calling from C or FORTRAN,
but having NO difference in the CDF file ids, is inconsistent and confusing.
The other question I had was pointed out in the comments in the FORTRAN
program--if you comment out the ncainq call, the next ncagtc call dies
with a ' NCAGTC: string won't fit in CHARACTER variable provided ' error
message! This is in spite of the fact that the C program syncs the cdf
file, and the variable is plenty big enough to hold the result. It
seems like a bug to me.
The above comments nonwithstanding, I really like the netCDF package (far
more than the hdf one), so thanks again for making it available.
--Dave Pierce pierce@xxxxxxxxxxxxxxxxxxxx
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