Include variable value when throwing exception

6 次查看（过去 30 天）
Jurgen vL
Jurgen vL 2019-5-21
回答： Steven Lord 2025-11-7
I have a function that throws a specific exception, and a try/catch block in a top-level function that handles it. I want to pass along the value of some variables in addition to the error message for debugging purposes. Typically cell array, string array or numerical matrix.
I'm guessing I would have to create a custom exception class for this?
Follow-up: Why is the default MException so restrictive? Is error handling like I described a bad practice?
  2 个评论
Marc Youcef
Marc Youcef 2020-3-22
I was looking for same thing as well. I hav objects being instantiated in a loop and when it fails I would like to know which index of instantiation failed.
Daniel
Daniel 2025-11-6
编辑：Daniel 2025-11-6
You can subclass MException and add any custom properties to do exactly that. See my answer.

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回答（2 个）

Daniel
Daniel 2025-11-6
编辑：Daniel 2025-11-6
To add custom data to an exception, subclass MException and add custom properties.
classdef MyException < MException
properties
Data
end
end
Then, in code, use your custom property as so:
try
ex = MyException('root:cause', 'error message');
ex.Data = 1234;
ex.throw()
catch ME
disp(ME.Data)
end
Steven Lord
Steven Lord 2025-11-7
Ran in:
Why not just build up the appropriate string containing the message with the information you want it to include then call error to throw an error with that message?
expectsOnlyScalar(pi)
Good, you passed in the scalar value 3.1416
expectsOnlyScalar(1:10)
Error using solution>expectsOnlyScalar (line 9)
I expected a scalar value but instead you passed in an array of size [1 10]!
function expectsOnlyScalar(x)
if isscalar(x)
disp("Good, you passed in the scalar value " + x)
else
msg = "I expected a scalar value but instead " + ...
"you passed in an array of size " + mat2str(size(x)) + "!";
error(msg)
end
end

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