catch or catch something? - Try, catch, end.

Hi, I'm using the try...catch...end to catch the error. I have seen different ways of using catch at different places and got slightly confused.

One place I saw: try ... catch ... end

And another place I saw: try ... catch err ... end

And at another place I saw: try ... catch ME ... end

I'm wondering in what cases should I use catch, and what cases I need to use catch followed by some words or variables?

Many thanks.

Lily

[Adam]

It's the same as most code really. Your usage will tell you which you need (there are only two options there though, the last two are the same, just with a different variable name). If you want to do something relative to a specific error then you need the variable in order to interrogate it, usually something like

try...
catch ME
   if strcmp( ME.identifier, someSpecificIdentifier )
      doSomething()
   else 
      rethrow( ME )
   end
end

Generally I would advise using the variable. If you don't need it Matlab will just underline it in orange anyway and tell you you can get rid of it.

Without testing the type of error you are literally catching every possible error though, which is dangerous. Even syntax errors will just get caught and reacted to the same as others.

Answer 1

[Rik]

If you take a look at the documentation, you can see that catch ME stores the exception (all error information) in the variable ME. This can be useful if there are multiple errors that you expect to occur, so you can vary your response based on information like the error ID.

You will also need the exception if you want to throw, rethrow or throwascaller.

Answer 2

[M]

According to the matlab doc, you should use:

try
  code1
catch
end

to catch any exception generated by the code1 and

try
  code1
catch ME
end

if you want to handle different types of errors generated by code1.