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Strange behavior when initializing empty cell in struct()

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Chandler
Chandler 2024-6-20
评论： Stephen23 2024-6-20
Structs initialized with an empty cell using both {} and cell.empty within a struct() returns an empty struct object.
The following function reproduces that:
function print_hello_world()
obj = struct(MyProp=123, MyOtherProp={}); % or MyOtherProp=cell.empty
disp(obj)
disp(isempty(obj))
end
The obj variable is empty when running print_hello_world.
I have resorted to the following to go around this issue:
function print_hello_world()
obj = struct(MyProp=123);
obj.MyOtherProp = {};
disp(obj)
disp(isempty(obj))
end
The value of obj is as expected when running the above.
  1 个评论
Stephen23
Stephen23 2024-6-20
"Structs initialized with an empty cell using both {} and cell.empty within a struct() returns an empty struct object."
Exactly as documented here: https://www.mathworks.com/help/matlab/ref/struct.html#d126e1620618

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回答（1 个）

Aquatris
Aquatris 2024-6-20
编辑：Aquatris 2024-6-20
Ran in:
If you want to define the property as empty, then you should use '[]' instead of '{}'.
obj = struct(MyProp=123, MyOtherProp=[]);
disp(obj)
MyProp: 123 MyOtherProp: []
This is an intended behaviour. Here is the relevant part of the documentation:
s = struct(field1,value1,...,fieldN,valueN) creates a structure array with multiple fields.
  • ...
  • If any value input is an empty cell array, {}, then output s is an empty (0-by-0) structure. To specify an empty field and keep the values of the other fields, use [] as a value input instead.

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