Comments on: Exceptional Behavior

By: Chris Rodgers

Chris Rodgers — Wed, 17 Dec 2008 13:28:41 +0000

Hi,

Two thought on exceptions and debugging:

1) Please can we have a way to access the workspace where an exception was thrown, like the dbup / dbdown functions for normal errors. This would make debugging much more powerful. At the moment, a “catch” block prevents one from investigating the error in more detail using the debugger.

2) Please can we have a facility to break when a named variable is assigned to. The Visual Studio C++ debugger has had this option for years and it is very helpful.

Thanks,

Chris.

By: Loren

Loren — Sun, 09 Dec 2007 18:31:21 +0000

Please contact technical support for more information. This is not an issue with try-catch or exceptions, the topic of the post.

–Loren

By: k

Sun, 09 Dec 2007 15:41:06 +0000

Thank you very much. Could I ask some more in detail, please?
For example, repeat ‘fscanf’ for 50 loops, but Matlab may cause a “timeout” error. I am not sure what I should put in the “catch” statement. (fclose and fopwn again here?)
–
try,
for 1+1:1:50,
measure = fscanf(s);
end
catch
end
–

By: Loren

Loren — Sun, 09 Dec 2007 15:25:41 +0000

You can use try-catch with pretty much anything. For a serial port, you just need to be sure to close or delete the port if things don’t work out.

–Loren

By: k

Sun, 09 Dec 2007 14:55:40 +0000

how try/catch can be applied for the functions for serial port? (e.g. fscanf, fprintf, and/or fopen)?

By: Loren

Loren — Mon, 12 Nov 2007 16:53:20 +0000

Shivani-

Two issues. First, you are not using the syntax correctly. Check the reference page for try/catch to show how to define the MException.

Second, perhaps you are not using the R2007b release. If not, you won’t have MExceptions available.

—Loren

By: Shivani Rao

Shivani Rao — Mon, 12 Nov 2007 16:50:55 +0000

I have been trying to use the try catch block in the new version of matlab R2007a and R2007b
I used the following syntax
try,
catch,

end

However i was unable to get this working

try,
catch, ME1,

end

It kept giving me the error “unknown identifier ME1″

How do we get access to the exception object in this case. None of the support and dicussion forums of matlab give an example of this.

Some help on this would be greatly appreciated

By: Tim Davis

Tim Davis — Thu, 01 Nov 2007 18:45:16 +0000

Well, that would be tricky, since sparse matrices didn’t exist in MATLAB until 4.0, I think (that’s also the version of MATLAB on my coffee mug “MATLAB 4 Picture the Power”).

So sure, can I port my codes so they can run on my MATLAB 4 coffee mug? A MathWorker is a machine that turns coffee into M-files, after all (and C/C++/Java/etc), so I’m sure you’re keen to port your codes back there too … :-)

By: Steve Eddins

Steve Eddins — Thu, 01 Nov 2007 17:22:24 +0000

Tim—Are you really interested in porting code back to run in versions ten years old or more? Like sparse linear algebra to MATLAB 3.5? :-)

By: Tim Davis

Tim Davis — Thu, 01 Nov 2007 16:45:40 +0000

Steve: Right … which means determining the version number in, say, MATLAB 5.0 is really important - you can’t use try/catch to port code back that far. And you can’t use

if (verLessThan (’MATLAB’,'5.0′))
…
end

because verLessThan doesn’t exist in that version. I think this would work instead, and should port to, say, MATLAB 2, even (whenever functions were introduced):

if (getversion <= 5)
… MATLAB 5 code here …
else
… etc.
end

where:

function v = getversion
v = sscanf (version, ‘%d.%d.%d’) ;
v = 10.^(0:-1:-(length(v)-1)) * v ;

returns 6.52 for version 6.5.2, and so on. It would return 3.2 if “version” returned a string “3.2 (whatever)”. However, the oldest MATLAB I have still running is 6.1.0 (R12.1) so I can’t test it on MATLAB 5.x or earlier.

So how old are “version”, “sscanf”, and “length” :-) ?