call function with fewer parameters

Question

aldo 2023-10-24

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2038101-call-function-with-fewer-parameters

回答： Voss 2023-10-24

采纳的回答： Voss

gg(a)

function gg(a,b,c)

end

what happen if i call function with 1 parameter instead of 3

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Torsten 2023-10-24

编辑：Torsten 2023-10-24

在 MATLAB Online 中打开

No need to explain this behaviour, I guess.

a = 2;
gg(a)
ans = 4
gg_error(a)
Not enough input arguments.

Error in solution>gg_error (line 10)
  result = a.^2 + b.^2;
function result = gg(a,b,c)
  result = a.^2;
end
function result = gg_error(a,b,c)
  result = a.^2 + b.^2;
end

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Answer 1

Voss 2023-10-24

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"what happen if i call function with 1 parameter instead of 3"

The answer depends on what the function does with the parameters.

I've defined two functions below: gg_1, which takes three inputs and uses the first one only, and gg_all, which takes three inputs and uses them all. Whether I call gg_1 with one input or two or three, it runs without error, but when I call gg_all with fewer than three inputs, an error occurs at the first line of code that tries to access an input that was not given. See below.

You can use nargin to determine how many inputs were given (and write code to handle different possible number of inputs).

a = 1;
b = 2;
c = 3;
gg_1(a,b,c)   % three inputs given; only the first is used; ok
     1
gg_1(a)       % one input given, which is used; ok
     1
gg_all(a,b,c) % three inputs given; all are used; ok
     1

     2

     3
gg_all(a)     % one input given; expected three; error
     1
Not enough input arguments.

Error in solution>gg_all (line 20)
disp(b); % error here if b is not given
% this function uses the first parameter only
function gg_1(a,b,c)
disp(a);
end
% this function uses all three parameters
function gg_all(a,b,c) 
disp(a); % error would happen here if a were not given
disp(b); % error happens here when a is given but b is not given
disp(c); % error would happen here if a and b were given but not c
end

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Answer 2

Walter Roberson 2023-10-24

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https://ww2.mathworks.cn/matlabcentral/answers/2038101-call-function-with-fewer-parameters#answer_1339786

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In MATLAB, it is not directly an error to call a function with fewer parameters than it is defined with.

Instead, at the time that you try to use one of the names defined as a parameter, if fewer parameters have been passed and you did not already assign to that variable, then you will get an error about not enough parameters.

aa = 123;
gg(aa)
a = 123
b = 456
c = 789
Not enough input arguments.

Error in solution>gg (line 11)
   d
function gg(a,b,c,d)
   if nargin < 2
       b = 456;
   end
   c = 789;
   a
   b
   c
   d
end

Here we do not pass in a value for b, but that is okay because we used nargin to detect the situation and assigned a default value for b.

Here we do not pass in a value for c, but that is okay because we ignored whatever c was passed in and always assigned a value to c before we tried to use it.

Here we do not pass in a value for d, and by the time we need d, we still have not assigned a value to d, so it is an error.