MATLAB: Purpose of error identifiers

errorexception handlingmessage identifiermexception

I am curious about the practical uses of error identifiers, for example the 'identifier' property in MException objects.

From the documentation (https://uk.mathworks.com/help/matlab/matlab_prog/capture-information-about-errors.html#bq9tdlq-1), I gather that the identifiers are tags for error statements that make them unique. The docs go on to say that the the identifiers can help better identify the error source and also be used to control the error display. The examples that follow however just show how identifiers are created and extracted, so I struggle to see how it can be useful over say, just returning the 'message' property itself.

Why make error statements unique? What is the utility of the identifiers?

Best Answer

It is common for the exact spelling and phrasing and formatting of error messages to evolve. When you go to try/catch an error it is inconvenient to have to update all of the various places that have a particular exact spelling and phrasing to be able to match the changes. Instead it is more convenient to use a token that does not change to represent the error for try/catch purposes, permitting the spelling and phrasing to be changed in just one place.

In particular, using a token to stand in is a practical necessity when you make the program multilingual. When you use a token (error identifier) you can try/catch on just one short representation of the condition and then program in "message catalogs" that hold the translation to a variety of human languages.

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MATLAB: How to save to a variable and/or file, an error message from a guide

In the code that you think might generate an error, instead of calling

   Some Statement Here

encode it in a try/catch block that does whatever you want with the error

   try
     Some Statement Here
   catch ME
     %deal with the error the way you need
     fprintf('Caught error "%s" with details "%s"\n', ME.identifier, ME.message);
   end

MATLAB: Catch terminal’s error message

As Walter says, your example script will never execute because of the syntax error so try catch inside the file is no good.

However, a try... catch statement in the caller of the file would trap the error. So:

try
   nameoflongscript   %invoke long script
catch ME
   disp(ME)
end

would work.

Alternatively, to detect such parse errors before actually running the script, you could use mlint to analyse the file, or the undocumented mtree to get the parse tree of the file. Either of these will tell you if there are any parse error.

Best Answer

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MATLAB: How to save to a variable and/or file, an error message from a guide

MATLAB: Catch terminal’s error message

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