When calling this function how is the input error caught

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Darnell Gawdin 2020-4-18

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评论： Walter Roberson 2020-4-18

This is a test function from the documentation. If I include a letter in the arguments instead of a number matlab reports an error. My question is how does matlab know its an error?

testValues(5,1,2,3,4,5,6,7,8,9,10,a)
function testValues(threshold,varargin)
    minInputs = 2;
    maxInputs = Inf;
    narginchk(minInputs,maxInputs);
    for k = 1:(nargin-1)
        if (varargin{k} > threshold)
            fprintf('Test value %d exceeds %d\n',k,threshold)
        end %endif
    end %endfor
end %end function

Thanks for any input, haha input get it!

D

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Answer 1

Mehmed Saad 2020-4-18

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编辑：Mehmed Saad 2020-4-18

在 MATLAB Online 中打开

since you include a letter a which Matlab think is a variable. so it try to pass the variable a to testValues but that variable doesnot exist so Matlab give you error

either you initialize the variable a

a =1;
testValues(5,1,2,3,4,5,6,7,8,9,10,a)

or you can use string to pass the letter

testValues(5,1,2,3,4,5,6,7,8,9,10,'a')

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Darnell Gawdin 2020-4-18

hahahahah, Doh!. Yes of course. Thanks! :) Sorry its been a long day.

Walter Roberson 2020-4-18

right. A letter would be a variable name or function name, and matlab would do name resolution. If it were a variable then the value of the variable would be passed down, and you would only be able to tell that apart from numeric constant by examining argname(). If it were a function name (not anonymous function as those are variables or expressions) then it would try to evaluate the function with no parameters and pass the first output into the testValues.

MATLAB would never look and say "Ah hah, you passed a name here instead of a numeric constant!". You can probe that with argname if you really want but argname cannot tell the difference between you passing in 10 and you passing in a+0 where a happens to contain 10: both show up with argname empty.

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