MATLAB Answers


Access arbitrary class from MATLAB Engine interface

Asked by Szabolcs
on 11 Feb 2013

Using the MATLAB Engine interface, it is possible to access most data types such as numerical arrays, cells, structs, etc.

Is it also possible to access arbitrary classes such as an MException? If so, how? Just access the fields using mxGetField() etc. as in the case of structs? I am interested in MException in particular.

EDIT: I tried this, but unfortunately MATLAB (not the engine program, but the MATLAB process) crashes whenever I tried to call engGetVariable() on a variable of class MException. I'm on OS X. I would appreciate any suggestions about possible workarounds. Note that because of this crash, it is simply not safe to pass arbitrary variable names to engGetVariable(). There's always a chance it would crash MATLAB.


2 Answers

Answer by Amro
on 19 Feb 2013
 Accepted answer

A trick is to convert any OOP class object to a regular structure in the MATLAB side:

ME = MException('a:b','err');
s = struct(ME);

Note that a warning is issued that any private, protected, or hidden properties of the object will become public fields in the new structure:

>> s
s = 
             type: {[0]  ''}
    hasBeenCaught: 0
       identifier: 'a:b'
          message: 'err'
            cause: {}
            stack: [0x1 struct]
     defaultstack: [0x1 struct]
        arguments: {}

Now you can retrieve the new variable using the Engine API, and handle it as a regular structure:

mxArray *s = engGetVariable(ep, "s");
mxArray *identifier = mxGetField(s, 0, "identifier");
mxArray *message = mxGetField(s, 0, "message");


Thanks for the answer! One missing piece is that I'd actually need to recurse deep on any struct/cell/class and convert every class within to structs. The crash would happen if I try to engGetVariable a struct or cell which contains a class arbitrarily deep inside.

on 19 Feb 2013

ah, hadn't thought of that.. I guess you can traverse the structure fields recursively and use isobject() to check if its an class object or not (in the MATLAB side of course)

Answer by Jing
on 19 Feb 2013

First, I'm not familiar with MATLAB Engine. If I misunderstand your question, just ignore me.

The MException object is accessible in MATLAB program. It's an object, so you can access it's property like other class. It's similar to structs. For example, you have a MException object ME, just type ME.message in the command window, you can get the message out of it.

  1 Comment

I'm afraid you misunderstood the question. This is about about accessing the class from the C language, not from MATLAB.

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