Conditional try catch statement in matlab

Question

I am looking for an elegant way to use a conditional try catch statement.

I suppose it could look something like this:

tryif loose==1
% Do something, like loading the user preferences
catch %Or catchif?
% Hande it
end

So far I know that you can use try catch blocks to let your compiled code run, but force it to stop in a debug session with dbstop if caught error. Now I am basically looking for the opposite:

Normally I want the code to stop if unexpected situations occur (to guarantee the integrity of results) but want to be less strict about certain things sometimes when I am debugging.

There seems to be a big difference between the hypothetical tryif and catchif statements. For tryif I imagine it would not try the code, whereas with catchif it would always try, but not always catch. Are you after catchif? — chappjc
– chappjc, Commented Nov 15, 2013 at 18:12
@chappjc I always want to Do something, but just want to controll whether I am forgiving when it fails. The accepted answer seems to be exactly what I was looking for. — Dennis Jaheruddin
– Dennis Jaheruddin, Commented Nov 16, 2013 at 11:55

A. Donda · Accepted Answer · 2013-11-15 14:43:13Z

5

How about this:

try
  % Do something, like loading the user preferences
catch exception
  if loose ~= 1
    rethrow(exception)
  end
  % Handle it
end

I don't know about elegant ;-), but at least it avoids the duplication of "do something".

answered Nov 15, 2013 at 14:43

A. Donda

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Comments

Dennis Jaheruddin · Accepted Answer · 2013-11-15 14:27:07Z

1

I know one way to do it, though I would hardly call this elegant:

if loose == 1
  try
    % Do something, like loading the user preferences
  catch
    % Hande it
  end
else
  % Do something, like loading the user preferences
end

answered Nov 15, 2013 at 14:27

Dennis Jaheruddin

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2 Comments

sebastian Over a year ago

Imho it's as elegant as any other if/else block. You also wouldn't want to invent a forif or continueif etc.

Dennis Jaheruddin Over a year ago

@sebastian It is as elegant as any if else block, but not as elegant as any try catch block as this answer requires duplication. However from the other answer it seems there is a way around this.

Pursuit · Accepted Answer · 2013-11-15 16:19:11Z

1

The best I've been able to do is:

try
    % Do something, like loading the user preferences
catch me
    errorLogger(me);
    %Handle the error
end

And then

function errorLogger(me)
LOOSE = true;    
%LOOSE could also be a function-defined constant, if you want multiple uses.  
%    (See: http://blogs.mathworks.com/loren/2006/09/13/constants/)

if LOOSE
    %Log the error using a logger tool.  I use java.util.logging classes, 
    %but I think there may be better options available.
else
    rethrow(me);
end

Then, if desired for production-style deployments, avoid the constant condition checking like this:

function errorLogger(me)
%Error logging disabled for deployment

answered Nov 15, 2013 at 16:19

Pursuit

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3 Comments

A. Donda Over a year ago

Well, except for the logging thing this is exactly the same solution as mine. An acknowledgement of that would have been nice.

Pursuit Over a year ago

It seems to me the goals of this problem are: (1) minimize code clutter, and especially reuse, at the point the error could occur; (2) provide the clean, and low-overhead options for switching between error handling modes. I have found that functionalizing the inner IF statement helps with both of these goals. Error logging is just an added bonus which is relevant to my current real world activities, and therefore shows up in all my thoughts. :)

Dennis Jaheruddin Over a year ago

Gave you +1, mostly for the comments that go with the answer. It is indeed nice to have a solution usable in 1 line, but I suppose I could just put the code by @A.Donda in a script. --- Sidenote, it is I plan to take advantage of isdeployed for setting the right condition automatically in most situations.

chappjc · Accepted Answer · 2013-11-15 18:15:43Z

1

For the "tryif" functionality, you could assert on the first line of the try block:

try
    assert(loose==1)
    % Do something
catch err
    if strcmp(err.identifier,'MATLAB:assertion:failed'),
    else
    % Hande error from code following assert
    end
end

Note that the "Do something" code will not be executed if loose==1.

For the "catchif" functionality, A.Donda's approach of checking loose~=1 on the first line of the catch block seems quite good.

edited Nov 15, 2013 at 18:15

answered Nov 15, 2013 at 17:55

chappjc

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