MATLAB: How to handle BOTH MException and MSLException

MATLABmexceptionmslexceptionsimulink

I am very experienced with exceptions in C++ so the concept is nothing new to me. However. implementing it in the Mathworks world is. I have a handler function that I want to accept a generic exception object and inside the handler determine which exception ofject it is and act based on that determination. "isa" doesn't work since it returns a 1 regardless if I check it for MSLException or MException.

Bottom line, if I could figure out a way to determine if an exception object was either a MSLException or a MException then I can take it from there.

Any ideas?

Best Answer

I just figured out a workable solution.

"my_exception" is an exception object generated by my program.

 if (strcmp('MSLException',class(my_exception)))
     Temp_exception = MException(my_exception.identifier, my_exception.message);
     Temp_exception = addCause(Temp_exception, my_exception);
      % store exception info
      SAVE_MY_EXCEPION(Temp_exception); 
  else
      % it isn't so store my_exception info
      SAVE_MY_EXCEPION(my_exception); 
  end

Sure I sacrifice the MSLException handle information, but I get to store the exception information. I'd love to create storage for MSLException objects, but I don't see how to create that object. Creating it the same way as a MException doesn't work. a = MSLException('tempidentifier', 'tempmessage'); fails.

Related Solutions

MATLAB: Can I throw an empty MException object using THROW, RETHROW, or THROWASCALLER in MATLAB 7.12 (R2011a)

The ability to throw an empty MException object using THROW, RETHROW and THROWASCALLER is not available in MATLAB. To work around this issue, use a condition statement to bypass the use of an empty MException Object:

errobj = MyIsEqual(params)
if isempty(errobj)
  % do nothing
else
  throwAsCaller(errobj)
end

Using condition statements whenever an empty MException object is given, however, may affect the conciseness of the code.

MATLAB: How to replace the LASTERROR function in the MATLAB code with the try-catch exception method

This change has been incorporated into the documentation in Release 2010a (R2010a). For previous releases, read below for any additional information:

The use of the functions LASTERR and LASTERROR is no longer recommended for capturing the state of the last error. It is suggested to replace the use of these functions with the new style of try-catch statement that captures an MException object to represent the error. This is because LASTERROR and LASTERR functions kept track of only the one most recently thrown error. The state of any errors thrown before that was overwritten by newer errors. Also, this error state was globally accessible, which means that it could be unintentionally modified or destroyed either during an interactive session or by another function. As in the example below,

% This code will NOT work in future releases





try
aUserDefinedFunction;
catch
someFunction;
rethrow(lasterror);
end

if someFunction did not guard against modification of lasterror as seen above, and doSomeStuff threw an error, then the rethrow(lasterror) would

rethrow the wrong error. In the following document, the function LASTERROR is meant to include both LASTERROR and LASTERR functions.

Below are some suggestions of how to replace some of the most common uses of the functions LASTERR and LASTERROR with equivalent TRY-CATCH Exception errors:

1. The data that is available from the functions LASTERROR and LASTERR can also be accessed using the properties of the MException object created with the TRY-Catch block. These properties can then be used to:

a. rethrow the last error message. As an example, replace this code

% This code will NOT work in future releases
try
    ...
catch
    rethrow(lasterr) % or rethrow(lasterror)
end

with

% This code will work




try
    ...
catch myException
    rethrow(myException) % or throw(myException), throwAsCaller(myException)
end

b. modify the appearance of the displayed error message (like remove "Error using ==>" ) or the message string. As an example, replace this code

% This code will NOT work in future releases
try
    ...
catch
    ...
    msg = strrep(lasterr,xlate('Error using ==>'));
    error(msg);
    ...
end

with

% This code will work
try
    ...
catch myException
    ...
    throw(myException)
end

c. use the last error message to throw a warning. As an example, replace this code:

% This code will NOT work in future releases
[prev, ID] = lasterr;
try
    ...
catch
    ...
    lasterr('reset') % OR lasterr('') OR  lasterr(prev,ID)
end

with

% This code will work
try
    ...
catch myException
    warning(myException.identifier, '%s', myException.getReport('basic')); 
end

2. The special case when the LASTERROR function is being used to get the error message thrown from a statement in the EVAL or the EVALC command can be replaced with the following equivalent try-catch syntax. As an example, replace this code

% This code will NOT work in future releases
eval('doStuffThatErrors;', 'myError=lasterror; doErrorHandlingStuff(myError)');

with

% This code will work
try
      eval('doStuffThatErrors;');
catch myError
      doErrorHandlingStuff(myError)
end

3. When used in a PARFOR loop, the name of the MException variable needs to be preallocated before the PARFOR. As an example, replace this code

% This code will NOT work in future releases
function testParfor 
parfor i = 1:10 
     try
         error('oups');
     catch err
         disp(err.getReport);
     end
end

with

% This code will work
   err = [ ];
parfor i = 1:10 
     try
         error('oups');
     catch err
         disp(err.getReport);
     end
end

Best Answer

Related Solutions

MATLAB: Can I throw an empty MException object using THROW, RETHROW, or THROWASCALLER in MATLAB 7.12 (R2011a)

MATLAB: How to replace the LASTERROR function in the MATLAB code with the try-catch exception method

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