Preventing too many function inputs

Question

Samuel Brewton 2021-2-22

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编辑： Stephen23 2021-2-22

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!

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Answer 1

per isakson 2021-2-22

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https://ww2.mathworks.cn/matlabcentral/answers/752189-preventing-too-many-function-inputs#answer_629559

编辑：per isakson 2021-2-22

在 MATLAB Online 中打开

>> 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

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per isakson 2021-2-22

在 MATLAB Online 中打开

I guess you discovered my error

nargin >= 3

should be

nargin >= 4

Stephen23 2021-2-22

编辑：Stephen23 2021-2-22

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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Preventing too many function inputs

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