work with all csv files

@tsg_nc/get_fieldnames.m

 function result = get_fieldnames( self )
 
-% tsg_ncvar/get_fieldnames -- get internal fieldnames of "tsg_ncvar" object.
+% tsg_nc/get_fieldnames -- get internal structure fieldnames of "tsg_nc" object.
 %
 % Input
 % -----
-% self     ........... an instance of 'tsg_ncvar' object
+% self     ........... an instance of 'tsg_nc' object
 %
 % Output
 % ------
@@ -12,7 +12,14 @@ function result = get_fieldnames( self )
 
 % $Id$
 
-theStruc = get(self,'DAYD');
-result = fieldnames(theStruc);
-    
+% get cell of keys inside object
+% ------------------------------
+c = get(self);
+if isempty(c)
+  warning('Empty object') ;
+else
+ % get structure for the first element
+ theStruc = get(self,c{1});
+ result = fieldnames(theStruc);
+end