How to access struct member via a string

Question

Danny 2023-10-5

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https://ww2.mathworks.cn/matlabcentral/answers/2029814-how-to-access-struct-member-via-a-string

编辑： Bruno Luong 2023-10-6

Let's say I create a struct via the following:

airplane.cockpit.controls.throttle = 'forward'
airplane = struct with fields:
    cockpit: [1×1 struct]

I can access those fields like this:

airplane.('cockpit').('controls')
ans = struct with fields:
    throttle: 'forward'

Is it possible to use these semantics but with a string representation? I've tried this:

s = "('cockpit').('controls')"
s = "('cockpit').('controls')"
airplane.(s)
Unrecognized field name "('cockpit').('controls')".

Reason for asking is that I have a configuration file that use the same structure notation to "drill" down into the structure. I'd like to be able to read that configuration file to access certain members of the struct

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Stephen23 2023-10-5

编辑：Stephen23 2023-10-5

"Is it possible to use these semantics but with a string representation?"

Not easily. But you can easily use SPLIT and GETFIELD.

An explanation of why your approach does not work: https://www.mathworks.com/matlabcentral/answers/1656435-tutorial-comma-separated-lists-and-how-to-use-them#answer_966455

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Answer 1

Matt J 2023-10-5

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编辑：Matt J 2023-10-5

在 MATLAB Online 中打开

Here is something simiilar:

airplane.cockpit.controls.throttle = 'forward';
s={'cockpit','controls'};
getfield(airplane,s{:})
ans = struct with fields:
    throttle: 'forward'

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Fangjun Jiang 2023-10-5

在 MATLAB Online 中打开

airplane.cockpit.controls.throttle = 'forward';
s = "('cockpit').('controls')";
pth=extractBetween(s,"'","'");
getfield(airplane,pth{:})
ans = struct with fields:
    throttle: 'forward'

Danny 2023-10-5

Thank you! This is very close to what I was looking for

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Answer 2

Bruno Luong 2023-10-5

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https://ww2.mathworks.cn/matlabcentral/answers/2029814-how-to-access-struct-member-via-a-string#answer_1327059

编辑：Bruno Luong 2023-10-6

在 MATLAB Online 中打开

I made this for my own use. It is not a dot syntax, just the functional form.

The constraint is that accessing nested subfield(s) should be scalar.

Assignment automatically creates the intermediates nested structures if they do not exist.

Error handling when retreive if the intermediate/final nested structures do not exist.

airplane = struct()
airplane = struct with no fields.
airplane = rsetfield(airplane, 'cockpit.controls.throttle' , 'forward')
airplane = struct with fields:
    cockpit: [1×1 struct]
airplane.cockpit.controls.throttle
ans = 'forward'
[value success] = rgetfield(airplane, 'cockpit.controls.throttle')
value = 'forward'
success = logical
   1
[value success] = rgetfield(airplane, 'cockpit.controls.alarm')
value =

     []
success = logical
   0