text: function val=jsonopt(key,default,varargin)
  %
  % val=jsonopt(key,default,optstruct)
  %
  % setting options based on a struct. The struct can be produced
  % by varargin2struct from a list of 'param','value' pairs
  %
  % authors:Qianqian Fang (fangq<at> nmr.mgh.harvard.edu)
  %
  % $Id: loadjson.m 371 2012-06-20 12:43:06Z fangq $
  %
  % input:
  %      key: a string with which one look up a value from a struct
  %      default: if the key does not exist, return default
  %      optstruct: a struct where each sub-field is a key 
  %
  % output:
  %      val: if key exists, val=optstruct.key; otherwise val=default
  %
  % license:
  %     BSD license, see LICENSE_BSD.txt files for details
  %
  % -- this function is part of jsonlab toolbox (http://iso2mesh.sf.net/cgi-bin/index.cgi?jsonlab)
  % 
  
  val=default;
  if(nargin<=2) return; end
  opt=varargin{1};
  if(isstruct(opt) && isfield(opt,key))
      val=getfield(opt,key);
  end
  
  