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Re: variable string in attribute and char variables

>To: address@hidden
>From: Igor Pesenson <address@hidden>
>Subject: Re: 20030203: subject
>Organization: Lawrence Berkeley National Laboratory
>Keywords: 200302031956.h13Ju0623075

Hi Igor,

>    I've only recentely started using cdf and I have two, hopefully
> simple, questions.
> 1) I'm trying to document an attribute in the following way (taken from
> someone else's file):
>         int base_time ;
>                 base_time:string = "12-Nov-2002,0:00:00 GMT" ;
>                 base_time:long_name = "Base time in Epoch" ;
> But I can't figure out how to do this. I've created a char variable to
> hold the "string" value, but I can't seem to put it in properly. My code
> says:
> 
> char base_time_str[25];
> nc_status=nc_def_var(ncid,"base_time",NC_INT,0,&idimid,&ivarid[1]);
> nc_status=nc_put_att_text(ncid,out.ivarid[1],"string",strlen(base_time_str),
> base_time_str);
> 
> and it fails with the result of:
> 
>         int base_time ;
>                 base_time:string = "" ;
> The cdf documentation requires that the base_time_str was type "const
> char" but this would prevent it changing from file to file. Am I
> horribly misguided?

I think 

> nc_status=nc_put_att_text(ncid,out.ivarid[1],"string",strlen(base_time_str),
> base_time_str);

should instead be

  nc_status=nc_put_att_text(ncid,ivarid[1],"string",strlen(base_time_str),
  base_time_str);

given that you stored the variable ID in "ivarid[1]".  I've appended a
C program generated by using "ncgen -c igor.cdl" that seems to work,
if you need a complete example.  I used the following CDL file for
input to ncgen:

netcdf igor {
variables:
        int base_time ;
                base_time:string = "12-Nov-2002,0:00:00 GMT" ;
                base_time:long_name = "Base time in Epoch" ;
}

I'll send a separate reply to your second question, assuming I can
figure it out.

--Russ

#include <stdio.h>
#include <stdlib.h>
#include <netcdf.h>

void
check_err(const int stat, const int line, const char *file) {
    if (stat != NC_NOERR) {
           (void) fprintf(stderr, "line %d of %s: %s\n", line, file, 
nc_strerror(stat));
        exit(1);
    }
}

int
main() {                        /* create igor.nc */

   int  ncid;                   /* netCDF id */

   /* variable ids */
   int base_time_id;

   /* rank (number of dimensions) for each variable */
#  define RANK_base_time 0

   /* enter define mode */
   int stat = nc_create("igor.nc", NC_CLOBBER, &ncid);
   check_err(stat,__LINE__,__FILE__);

   /* define variables */

   stat = nc_def_var(ncid, "base_time", NC_INT, RANK_base_time, 0, 
&base_time_id);
   check_err(stat,__LINE__,__FILE__);

   /* assign attributes */
   stat = nc_put_att_text(ncid, base_time_id, "string", 23, 
"12-Nov-2002,0:00:00 GMT");
   check_err(stat,__LINE__,__FILE__);
   stat = nc_put_att_text(ncid, base_time_id, "long_name", 18, "Base time in 
Epoch");
   check_err(stat,__LINE__,__FILE__);

   /* leave define mode */
   stat = nc_enddef (ncid);
   check_err(stat,__LINE__,__FILE__);
   stat = nc_close(ncid);
   check_err(stat,__LINE__,__FILE__);
   return 0;
}