nc_open/nc_close problem

// Test function testing strings.
int rv, ncid;
if(rv = nc_create(fname, NC_NETCDF4, &ncid))
    goto error;     // Error opening file.

char *string = malloc(250);
sprintf(string, "This is a string.");

nc_put_att_string(ncid, NC_GLOBAL, "string1", 1, &string);

char *string2 = "This is also a string";
nc_put_att_string(ncid, NC_GLOBAL, "string2", 1, &string2);

free(string);

nc_close(ncid);
return rv;

/******* nc_open call: ********/
// Open the netCDF file.
if(rv = nc_open(fname, NC_NOWRITE, &ncid))
        goto error;

/******* nc_close call: ********/
if(ncid >= 0)
     nc_close(ncid);