Good morning,
I am using the NetCDF library and the C interface to write and modify
variables in an exsisting NetCDF file; specifically, I am addidng a single
date value as relative (or absolute according to the use) to some files that
were generated without a date (0000-00-00).
I need them to have a date specified in order to make operations on them using
CDO or NCL.
I can perfectly write the missign date and have a new file with the date as I
want it, but the position of the value is put is at the very end of the file
by default.
Is there a way to control the position inside the file where the variable
value is added?
I need to put it in a certain position because when I use CDO to merge several
files, the output merged file does not have a date anymore.
I hope I explained the problem well, if not, please contact me
Kind regards
Simone.
Here the code in C that opens and modify an exsisting *.nc file
///////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
C Code that uses the NetCDF library for entering and modifying the files:
///////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<netcdf.h>
main(int argc, char *argv[])
{
const char *fileANDpath[128];
int status;
//Error status
int ncid;
//NetCDF ID
int time_dim;
//Dimension ID
int time_id;
//Variable ID
int time_dimids[0];
//Variable shape
int ndims, nvars, ngatts, unlimdimid; //Existing variables
characteristics
static char time_att1[] = "day as %Y%m%d.%f";
// static char time_att1[] = "days since ";
char *s2;
strcat(time_att1,s2);
static size_t time_index[] = {0,0}; //Value starting from
the reference.
static double time_val; //Variable "ex.
19900101"
//If the number fo raguments is at least 1, then the program will execute from
here:
/****************/
/***User inputs**/
/****************/
static char time_att2[] = "gregorian";
static char time_att3[] = "time";
/****************/
/*END Inputs*****/
/****************/
/***********************************************************/
/*Preliminary computations to prepare some strings**********/
/***********************************************************/
//Take the terminal input of the path and file name
*fileANDpath = argv[2];
printf("\n - PATH = %s\n", *fileANDpath);
//Take the second input from the executable: argv[2]
s2 = argv[2];
strcat(time_att1, s2);
//Open dataset to access it in read-only (putting 0 instead of
NC_WRITE) or
read-write mode:
status = nc_open(*fileANDpath, NC_WRITE, &ncid);
if(status != NC_NOERR) printf("Error in Opening file\n");
else printf("\nOK - File open with ID: %d\n", ncid);
status = nc_inq(ncid, &ndims, &nvars, &ngatts, &unlimdimid);
printf("\n File: %s\n\n - ID = %d\n - ndims = %d\n - nvars =
%d\n - ngatts =
%d\n - unlimdimid = %d\n\n", *fileANDpath, ncid, ndims, nvars, ngatts,
unlimdimid);
//Put the dataset in define mode to add dimensions, variables or
attributes:
status = nc_redef(ncid);
if(status != NC_NOERR) printf("Error in Opening file\n");
else printf("OK - File in define mode now\n");
//Define dimensions, variables, attributes
//A) Define dimensions for the "time" variable:
status = nc_def_dim(ncid, "time", NC_UNLIMITED, &time_dim);
//B) Define variable:
time_dimids[0] = time_dim;
status = nc_def_var(ncid, "time", NC_DOUBLE, 1, time_dimids,
&time_id);
//C) Define Attributes:
status = nc_put_att_text(ncid, time_id, "units", strlen(time_att1),time_att1);
status = nc_put_att_text(ncid, time_id, "calendar", strlen(time_att2),
time_att2);
status = nc_put_att_text(ncid, time_id, "long_name", strlen(time_att3) ,
time_att3);
//D)Leave define mode, checking consistency of additions:
status = nc_enddef(ncid);
if(status != NC_NOERR) printf("Error in creating the
variable\n");
else printf("OK - Variable created\n");
//E) Write a single data value: nc_put_var1_type: argv[1]
time_val = atof(argv[1]);
status = nc_put_var1_double(ncid, time_id, time_index,
&time_val);
if(status != NC_NOERR) printf("Error in nc_put_var1_type the
variable\n");
else{
printf("OK - Value Added to the file\n");
printf("time_value = %.0f\n",time_val);
}
//Close the file and write it:
status = nc_close(ncid);
//Call the bash and view the file created:
//
system("ncdump
/home/smarras/Documents/climateData/GISSdata/PROVA_ncmodifyFiles/decade_1980.ij.nc
> ncdump_output");
// system("pico ncdump_output");
return 0;
}
--
Simone Marras, Ph.D. Student
BSC & Universitat Politecnica de Catalunya
Jordi Jirona 29
08034 Barcelona
Spain
--
Simone Marras, Ph.D. Student
BSC & Universitat Politecnica de Catalunya
Jordi Jirona 29
08034 Barcelona
Spain
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