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Preventing too many function inputs

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Samuel Brewton
Samuel Brewton on 22 Feb 2021
Edited: Stephen Cobeldick on 22 Feb 2021
I am looking for a way to prevent a user from putting in too many inputs for a function. Here is a quick code example:
exfunction(1,3,9)
function exfunction(x,y,z)
switch nargin %Checking # arguements
case 3 %3 function arguements
a=x+y; %Adds x and y
b=x*z; %Multiplies x and z
disp([a,b]); %Displays a and b
otherwise %Less than 3 function arguements (Doesn't work for more than 3)
disp('Wrong Number of Arguements')
end %End switch
end %End function
This function has 3 inputs: x, y, and z. If the user were to only define x and y, it would display "Wrong Number of Arguements" without issue. However, if the user added 4, 5, or any number over the 3 variables, MatLab tries to define the variable (which doesn't exist) and gives me an error.
Any help is appreciated, thanks!

Answers (1)

per isakson
per isakson on 22 Feb 2021
Edited: per isakson on 22 Feb 2021
>> exfunction(1,3,9,4,5)
throws the error
Error using exfunction
Too many input arguments.
I assume that's the error you encounter and that you want it to handle the situation more gracefully.
Replace
function exfunction(x,y,z)
by
function exfunction( varargin )
if nargin >= 3
disp( 'Too many input arguments. Three anticipated' )
return
else
x = varargin{1};
y = varargin{2};
z = varargin{3};
end
Now
>> exfunction(1,3,9,4,5)
will display
Too many input arguments. Three anticipated
  3 Comments
Stephen Cobeldick
Stephen Cobeldick on 22 Feb 2021
Note:
  • using varargin means you will not get useful, meaningful information via tab completion or function hinting.
  • Throwing an error is the standard, easy way to handle this. If incorrrect inputs are provided, why let the code continue? This indicates a syntax problem that need to be fixed, not ignored.
Is there a particular reason why throwing an error does not work for you?

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