How do I access structrure fields from input parser optional inputs

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Ron on 5 Apr 2015
Commented: Ron on 6 Apr 2015
I am trying to pass in one and optionally two structures of the same type to a function using the input parser. I can access the fields of the first required structure, but I can't access the fields of the second optional structure. For the sample code below, a call of
works fine, but a call of,
ptest(s1, 's2', s2)
returns an error message of
Undefined variable "s2" or class "s2.dpri".
Error in ptest (line 22) fprintf('s2 field 1: %f\n', s2.dpri)
Here is the sample code:
function [] = ptest( s1, varargin )
%%Input Parser
p = inputParser;
p.StructExpand = false;
% Defaults for optional input
default_s2 = 'none';
addRequired(p,'s1', @(x) isstruct(x));
addParameter(p,'s2', default_s2, @(x) isstruct(x));
% Check if optional parameters were specified
opt.s2 = ~any(strcmp('s2',p.UsingDefaults));
%%Actions based on s1
fprintf('s1 field 1: %f\n', s1.dpri)
fprintf('s1 field 2: %f\n', s1.dsec)
%%Actions based on s2
if opt.s2
fprintf('s2 field 1: %f\n', s2.dpri)
fprintf('s2 field 2: %f\n', s2.dsec)

Accepted Answer

Mohammad Abouali
Mohammad Abouali on 5 Apr 2015
Edited: Mohammad Abouali on 5 Apr 2015
That's not how varargin works if you have
function ptest(s1,varargin)
then once you call it as:
to access s2 within ptest you need to use varargin{2} for example you need to change the following part of your code as shown here
%%Actions based on s2
if opt.s2
%fprintf('s2 field 1: %f\n', s2.dpri)
%fprintf('s2 field 2: %f\n', s2.dsec)
fprintf('s2 field 1: %f\n', varargin{2}.dpri)
fprintf('s2 field 2: %f\n', varargin{2}.dsec)
alternatively you can access it using your parser object variable (p) as follow
This works if you have setup the parser object properly of course.

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