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6.26 Read a Single Data Value: nc_get_var1_ type

The functions nc_get_var1_ type get a single data value from a variable of an open netCDF dataset that is in data mode. Inputs are the netCDF ID, the variable ID, a multidimensional index that specifies which value to get, and the address of a location into which the data value will be read. The value is converted from the external data type of the variable, if necessary.

The functions for types ubyte, ushort, uint, longlong, ulonglong, and string are only available for netCDF-4/HDF5 files.

The nc_get_var1() function will read a variable of any type, including user defined type. For this function, the type of the data in memory must match the type of the variable - no data conversion is done.

Usage

     int nc_get_var1_text  (int ncid, int varid, const size_t index[],
                            char *tp);
     int nc_get_var1_uchar (int ncid, int varid, const size_t index[],
                            unsigned char *up);
     int nc_get_var1_schar (int ncid, int varid, const size_t index[],
                            signed char *cp);
     int nc_get_var1_short (int ncid, int varid, const size_t index[],
                            short *sp);
     int nc_get_var1_int   (int ncid, int varid, const size_t index[],
                            int *ip);
     int nc_get_var1_long  (int ncid, int varid, const size_t index[],
                            long *lp);
     int nc_get_var1_float (int ncid, int varid, const size_t index[],
                            float *fp);
     int nc_get_var1_double(int ncid, int varid, const size_t index[],
                            double *dp);
     int nc_get_var1_ubyte (int ncid, int varid, const size_t *indexp,
                            unsigned char *ip);
     int nc_get_var1_ushort(int ncid, int varid, const size_t *indexp,
                            unsigned short *ip);
     int nc_get_var1_uint  (int ncid, int varid, const size_t *indexp,
                            unsigned int *ip);
     int nc_get_var1_longlong (int ncid, int varid, const size_t *indexp,
                               long long *ip);
     int nc_get_var1_ulonglong(int ncid, int varid, const size_t *indexp,
                               unsigned long long *ip);
     int nc_get_var1_string(int ncid, int varid, const size_t *indexp,
                            char **ip);
     int nc_get_var1       (int ncid, int varid,  const size_t *indexp,
                            void *ip);
ncid
NetCDF ID, from a previous call to nc_open or nc_create.
varid
Variable ID.
index[]
The index of the data value to be read. The indices are relative to 0, so for example, the first data value of a two-dimensional variable would have index (0,0). The elements of index must correspond to the variable's dimensions. Hence, if the variable is a record variable, the first index is the record number.
tp
up
cp
sp
ip
lp
fp
dp
Pointer to the location into which the data value is read. If the type of data value differs from the netCDF variable type, type conversion will occur. See Type Conversion.

Return Codes

Example

Here is an example using nc_get_var1_double to get the (1,2,3) element of the variable named rh in an existing netCDF dataset named foo.nc. For simplicity in this example, we assume that we know that rh is dimensioned with time, lat, and lon, so we want to get the value of rh that corresponds to the second time value, the third lat value, and the fourth lon value:

     #include <netcdf.h>
        ...
     int  status;                           /* error status */
     int ncid;                              /* netCDF ID */
     int rh_id;                             /* variable ID */
     static size_t rh_index[] = {1, 2, 3};  /* where to get value from */
     double rh_val;                         /* where to put it */
        ...
     status = nc_open("foo.nc", NC_NOWRITE, &ncid);
     if (status != NC_NOERR) handle_error(status);
        ...
     status = nc_inq_varid (ncid, "rh", &rh_id);
     if (status != NC_NOERR) handle_error(status);
        ...
     status = nc_get_var1_double(ncid, rh_id, rh_index, &rh_val);
     if (status != NC_NOERR) handle_error(status);