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Nested function not assigning value to global variable

Asked by Pal Szabo on 1 Sep 2017
Latest activity Commented on by John D'Errico
on 1 Sep 2017
Accepted Answer by KSSV
My main script invites a subfunction, which then invites different subfunctions. I want these subfunctions to modify global variables. A simpified example:
a=9;
b=2;
global p
myfunc(a,b);
display Result:
p
function [varargout] = myfunc(a,b);
arr=[a;b];
varargout={arr};
end
mysecondfunction(arr);
prod = arr(1)*arr(2);
p = prod;
end
When the main script calls p again it is empty. Why is this so and how can I fix it?

  3 Comments

"Nested function not assigning value to global variable"
Why are you using both nested functions and global variables?
Just use the nested functions. Global variables are evil, and should be avoided.
I'm trying to avoid them and write better code, now I've run into this problem and interested how to solve it.
UGH!!!!!!! Ugly, nasty code.
You solve the problem most easily by not using globals at all.
It is a bad idea to use globals in the first place. This is yet another reason why. You don't need globals. Most new users think they do, and eventually learn why not. But they make for nasty, bad code that will be difficult to debug.
As bad an idea is to use variables named prod, or other names that are already used for function names. When you name them that, the function prod will no longer work properly.

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2 Answers

Answer by KSSV
on 1 Sep 2017
 Accepted Answer

You have to assign p...you have not yet assigned it.
a=9;
b=2;
global p
p = rand ;
myfunc(a,b);
display Result:
p
function [varargout] = myfunc(a,b);
arr=[a;b];
varargout={arr};
end
mysecondfunction(arr);
prod = arr(1)*arr(2);
p = prod;
end

  3 Comments

KSSV, I try your script and it gives me back random p values after "Result:", not the product of a and b.
I was thinking you want to make a global variable in the main code and use it in every function without passing it....your criteria is different.....in this case....call it as a output from the function..not a global variable...

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Answer by Stephen Cobeldick on 1 Sep 2017
Edited by Stephen Cobeldick on 1 Sep 2017

Get rid of the global.
Globals do not solve anything, no matter how much beginners love using them.
It is not clear what your (buggy, non-working, incomplete) code is supposed to do, but making a nested function work correctly is very simple _when you avoid using evil global:
function p = test2
p = [];
myfunc(9,2);
function myfunc(varargin);
p = prod([varargin{:}]);
end
end
and tested:
>> test2()
ans = 18
And remember in future: if you even think of using global then your code design needs to be improved.

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