How to show the inputs to a function from within?

I'm trying to show (for debugging purposes) the input values to a function from within that function. If the inputs are provided through varargin, then a simple loop will do it:

output = myfun(varargin)
fprintf('\n%s was called with the following inputs:',mfilename)
for i = 1 : nargin
     fprintf('\n\t%s',varargin{i})
end

But if the function takes required inputs, then I cannot use the loop above but have to actually name all the inputs directly:

output = myfun(x,y,z)
fprintf('\n%s was called with the following inputs:',mfilename)
fprintf('\n\t%s',x)
fprintf('\n\t%s',y)
fprintf('\n\t%s',z)

This is cumbersome if there are many inputs. Also, it doesn't allow to copy-paste the nice loop to any function I want - I have to edit it for each function depending on the number and names of the inputs.

So the question is: Is there a way to do this with a loop? Essentially I would have to collect the input-names in a cell (like varargin) and then loop over that cell. But how to do this???

Note that the function inputname() doesn't solve this - it gives the name of the workspace variable, but I don't want the variable name, I want the value.

Thanks to everyone!

Answer 1

[Guillaume]

Matlab does not offer this kind of inspection functionality. The only way I could think of getting this would be to write your own function that would parse the m code of the function and use evalin to grab the values of all the inputs of the function. Something like:

%the function for which you want to see the inputs:
function output = myfun(x, y, z, varargin)
   displayinputs(mfilename('fullpath'));
   %rest of function ...
end

%function that parse and display inputs of another function:
function displayinputs(functionpath)
   %functionpath: the full path of the function m file. 
   %Obviously does not work for local subfunctions, nested functions, or class methods

     code = fileread([functionpath '.m']);
     [~, fname] = fileparts(functionpath);
     argsegment = regexp(code, sprintf('(?<=function.*?%s\\s*\\(\\s*)[a-zA-Z0-9_]+(?:\\s*,\\s*[a-zA-Z0-9_]+)*(?=\\s*\\))', fname), 'match', 'once');
     args = strsplit(argsegment, ',');
     fprintf('\n%s was called with the following inputs:\n', fname);
     for arg = args
        arg = strtrim(arg{1}); %#ok<FXSET>
        if strcmp(arg, 'varargin')
           vin = evalin('caller', 'varargin');
           for nin = 1:numel(vin)
              disp(vin{nin});
           end
        else
           varg = evalin('caller', arg);
           disp(varg);
        end
     end
  end

The above is totally untested and probably full of bugs. Note that the regular expression looking for the function declaration in the m file can easily be defeated by comments.

Also note, that the fprintf in your examples only work when the variables contain string.

edit: actually tested the function and fixed some bugs. It seems to work

Answer 2

[Yoel Lax]

Cumbersome, but nice! Thank you very much!!