How can I use NARGIN/NARGOUT to determine the number of input/output arguments of an object method?

I am trying to determine the number of input/output arguments of an object's method. When the name of any object method is passed to NARGIN/NARGOUT, the returned value is always -1 regardless of the number of inputs/outputs specified in the method signature.

The following syntax returns -1 for any MethodName:

nargout('MethodName')

Answer 1

[MathWorks Support Team]

The ability to call NARGIN/NARGOUT directly on object methods is not available in MATLAB. As a workaround, specify the class and method names explicitly using the following syntax:

nargout('ClassName>ClassName.MethodName')

Answer 2

[Markus Leuthold]

It's almost five years later and this bug still exists. Any news from Mathworks on how to handle this situation in 2015?

Example:

Class C

classdef C < handle
    methods
        function r=fcn1(~)
            r='run fcn1';
        end

          function fcn2(~)
              disp('run fcn2');
          end        
      end
  end

function run

function run(f)
switch nargout(f)
    case 0
        feval(f);
    case 1
        disp(feval(f));
    case -1
        disp('bug')
end

What I expect from the following code

>> c=C;
>> run(@c.fcn1)
run fcn1
>> run(@c.fcn2)
run fcn2

Instead I get

>> c=C;
>> run(@c.fcn1)
bug
>> run(@c.fcn2)
bug

How do you recommend to workaround in case where you want to know nargout from a function handle AND evaluate a function handle?

[Saurabh Harsh]

Hi Markus,

Please contact Mathworks technical support for additional questions regarding this. http://www.mathworks.com/support/contact_us/

Answer 3

[Eric Salemi]

I suggest you use the meta information provided by the MCOS class system:

>> class = ?containers.Map;
>> method = class.MethodList({mclass.MethodList.Name} == "subsref");
>> method.InputNames

ans =

    2×1 cell array

      'A'
      'S'

>> method.OutputNames

ans =

    cell

      'B'

It is reliable in most cases except when your class definition uses the old-style @ folder or if you query a non-MCOS class such as a Java class or such. On the side note, the accepted answer will not work for a qualified class such as above, which just shows that the NARGIN/NARGOUT functions are function-oriented are have not been adapted for the MCOS class system.

[Nikolaus Koopmann]

nice, thanks!

Answer 4

[Christopher Hummersone]

An indirect solution is to test for the existence of a particular variable:

exist('var_name','var')==1

This works for input variables; I haven't tested it for output variables.

[Madhav Rajan]

Although it helps, with exist you will need to the know the names of the variables that you want to track. NARGIN/NARGOUT makes it easier since you do not need any book keeping.

Answer 5

[Aruna Chhatkuli]

#include<stdio.h>
#define ROT 13

int main(void)
{
    int c,e;

    while((c=getchar())!=EOF)
    {
        if(c >='A' && c <='Z')
        {
            if((e = c + ROT) <= 'Z')
                putchar(e);
            else
            {
                   e = c - ROT;
                putchar(e);
            }
        }
        else if(c >='a' && c <='z')
        {
            if((e= c + ROT) <= 'z')
                putchar(e);
            else
            {
                e = c - ROT;
                putchar(e);
            }
        }
        else
            putchar(c);
    }

return 0;
}

[Aruna Chhatkuli]

please convert this code to matlab code

[Steven Lord]

This is unrelated to the original question. Please ask it as a separate question. When you ask it as a separate question, show what you've tried so far and you'll be more likely to receive a response.

[Walter Roberson]

That C code cannot be converted to MATLAB code. It uses getchar(), which reads from standard input, but MATLAB does not have standard input.