How to fix this error ? "attempt to reference field of non-structure array"

Hello, I had this error by declaring testset and classify as global variables. do you have an idea ? thank you

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[Stephen23]

Aaah, global variables and buggy code (that is almost impossible to debug).

Where is the variable defined? How many functions can access it? When and how is its value changed?

So many questions, and so few answers. Globals are the least recommended way of passing data between workspaces, and come second on this list of bad code practices:

https://blogs.mathworks.com/videos/2010/03/08/top-10-matlab-code-practices-that-make-me-cry/

Buggy, and all experts avoid using them... why would anyone even want to use them?

https://www.mathworks.com/matlabcentral/answers/51946-systematic-do-not-use-global-don-t-use-eval

https://www.mathworks.com/matlabcentral/answers/14857-where-do-people-learn-bad-programming-habits-i-e-goto-global-and-eval

http://www.mathworks.com/matlabcentral/newsreader/view_thread/20760

https://www.mathworks.com/matlabcentral/newsreader/view_thread/254555

Answer 1

[Jan]

Stephen's comment is exhaustive. Let me summarize it:

• Obviously the variable testset has not been defined before or not in the required way.
• Because it is a global variable, debugging is hard. You cannot directly find the code, which has (over-) written its value the last time.
• This is the expected and known problem with global variables. If the variables are provided as inputs, it is trivial to use the debugger to find the source of the last change.

Poor solution: Dig in your code until you find the bad declaration of the global variable.

Good solution: Remove the global variables from your code and use a clean providing of inputs and outputs - or even more secure an object oriented approach.

[houda mejri]

thanks a lot :)

[houda mejri]

In my case, the dataset and classifier are derived from the instructions in my matlab code. what can i do to get a clean providing of inputs and outputs ? Thanks

[Jan]

@houda: Now you can provide the dataset and teh classifier as inputs to myfunctiontominimize, see e.g. http://www.mathworks.com/matlabcentral/answers/1971

[houda mejri]

@jan Simon thanks a lot

Answer 2

[Joshah Magdalene]

I too have the same error.

Attempt to reference field of non-structure array.

I find this error in the below line of my code.

index = int32(pose.subset(j))+1;

I will be grateful if it is sorted out. Thank You!

[Walter Roberson]

Whatever your pose variable is, it is not a struct. One thing to check is whether it is [] as there are sequences of instructions that can leave a variable [] when you do not expect

For example

pose = []
for i = 1 : length(x)
  pose.data(i) = x(i).^2;
end

That sure looks like it sets pose as a struct with a field named data, but take a look at what happens if x is empty: length(emptiness) is 0 so the loop would not do any iterations and pose would be left as []

[Walter Roberson]

You posted about this somewhere else and I answered there

[Joshah Magdalene]

Thank you!

I have another query.

Is there any function like subset() and candidate() in Matlab?

If so what do they do?

Thanks in advance!

[Walter Roberson]

I do not find functions by those names in MATLAB. Possibly some third-party toolbox.