[Octave-bug-tracker] [bug #31706] mxDuplicateArray sometimes references (not: copies) the input data

[anonymous]

URL:
  <http://savannah.gnu.org/bugs/?31706>

                 Summary: mxDuplicateArray sometimes references (not: copies)
the input data
                 Project: GNU Octave
            Submitted by: None
            Submitted on: Fr 19 Nov 2010 11:47:40 UTC
                Category: None
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Incorrect Result
                  Status: None
             Assigned to: None
         Originator Name: Andreas Zoellner
        Originator Email: address@hidden
             Open/Closed: Open
         Discussion Lock: Any
                 Release: 3.2.4
        Operating System: Microsoft Windows

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Details:

For some inputs, the MEX function mxDuplicateArray only creates a reference
to, not a deep copy of, the input data.

Consider the following file "bug.cpp":

#include "mex.h"

#define X prhs[0]
#define Y plhs[0]

void mexFunction(int nlhs, mxArray *plhs[], int nrhs, const mxArray *prhs[])
{
  if (nrhs < 1) mexErrMsgTxt("One input argument required.");
  
  Y = mxDuplicateArray(X);
  double*const x = mxGetPr(X);
  double*const y = mxGetPr(Y);
  
  mexPrintf("mxArray: %x and %x\n", (int)X, (int)Y);
  mexPrintf("mxGetPr: %x and %x\n", (int)x, (int)y);
  
  if (x == y) mexWarnMsgTxt("Created only a reference, not a copy!");
  
  for (unsigned int i = 0; i < mxGetNumberOfElements(Y); ++i) y[i] = 1;
}



>> mex bug.cpp; x=1:3; y=bug(x); x, y


works as expected (x = [1 2 3]; y = [1 1 1];), but


>> mex bug.cpp; x = linspace(1,3,3); x, y


fails, overwriting the input (x = [1 1 1]; y = [1 1 1];)

Maybe this has something to do with lazy copying by data sharing?

----

Octave Version 3.2.4, official binary from Octave Forge
(http://sourceforge.net/projects/octave/files/Octave_Windows%20-%20MinGW/Octave%203.2.4%20for%20Windows%20MinGW32%20Installer/Octave-3.2.4_i686-pc-mingw32_gcc-4.4.0_setup.exe)





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