[Octave-bug-tracker] [bug #29475] new incompatibility of MEX function in Octave 3.2.x

[Xiangmin Jiao]

URL:
  <http://savannah.gnu.org/bugs/?29475>

                 Summary: new incompatibility of MEX function in Octave 3.2.x
                 Project: GNU Octave
            Submitted by: xjiao
            Submitted on: Thu 08 Apr 2010 03:56:01 PM GMT
                Category: Libraries
                Severity: 3 - Normal
              Item Group: Incorrect Result
                  Status: None
             Assigned to: None
         Originator Name: Xiangmin Jiao
        Originator Email: 
             Open/Closed: Open
         Discussion Lock: Any
                 Release: 3.2.3
        Operating System: GNU/Linux

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Details:

In Octave 3.2.x, if the MEX function changes an input mxArray containing a
character string, the change will not be propagated back to the caller. Some
MEX functions often use the trick of changing the input mxArray to pass an
in-out variable to achieve efficiency. This kind of MEX functions behaved
correctly in Octave 3.0.x (giving the same results as in MATLAB), but they
behave incorrectly in 3.2.x (giving different results from MATLAB). 

Since the main point of MEX functions if for comparability with MATLAB, a
different behavior from MATLAB should be considered as a bug. 

I suspect that Octave 3.2.x seems to have changed the behavior when passing a
character string to MEX functions. It seems to make a local copy of a
character string in an input mxArray before passing it to the MEX function. In
Octave 3.0.x, an input character string behaved the same as other data types,
i.e., it did not make a local copy.





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