Update a value in a struct in another function

I have a struct which is initialized by this:

function myStruct = defult_config

myStruct.myLenth = 1;

end

myStruct.myLength = 1 is an initial value and it needs to be updated by another fuction, myUpdate:

function out = myUpdate(myStruct)

myStruct.myLength = 2;

out = [];

end

However, myUpdate doesn't update myStruct and myStruct.myLength is still shown 1.

Any way to update a value in a struct by another function?

Answer 1

[dpb]

Variables in functions are local to the function and you don't return the struct; in fact in myUpdate you don't return anything at all...

function myStruct = myUpdate(myStruct)
  myStruct.myLength = 2;
end

You would have to use this in some context like

workingStruct=default_config;
...  % whatever else
workingStruct=myUpdate(workingStruct);
...  % more stuff...

This is going to be an awkward use pattern one imagines and unless there's a lot more than shown going on, simply writing

workingStruct=default_config;
...  % whatever else
workingStruct.myLength=newvalue;
...  % more stuff...

inline will probably be as legible code and easier...because unless the update value is a constant as shown, you're not providing it in the updating function and if you have to also add it as the second argument, then may as well just go ahead and update the struct itself directly.

Now, if there are some 20 other values as well, then mayhaps some similar structure may be desireable.

[Jay]

Thanks for clarification on how MATLAB works internally.

Answer 2

[Matt J]

You must return the modified myStruct from myUpdate():

myStruct.myLength = 1

myStruct = struct with fields:
    myLength: 1

myStruct = myUpdate(myStruct)

myStruct = struct with fields:
    myLength: 2

function myStruct = myUpdate(myStruct)

   myStruct.myLength = 2;

end