Re: Problem with mexPutVariable

[Bård Skaflestad]

On Wed, 2013-05-22 at 16:18 +0000, DONATI, KORY D CTR USAF AFSPC
WROCI/InDyne wrote:

> I asked a similar question previously that went unanswered. I have dug
>  into my problem more and have found what I think to be the root cause:
>  mexPutVariable. I am still new to using mex files and their language,
>  so I might not have my code correct.

It's been a while since I did any MEX coding so I'm hazy on the details,
but I do believe there is at least one misunderstanding in the code you
posted.  It is unrelated to mexPutVariable().

Specifically, the statements

> double arr1[5];

/* ... */

> /* Create an mxArray. */
>    array_ptr = mxCreateDoubleMatrix(1, 5, mxREAL);
>    
>    /*Set array to the mxarray*/
>    mxSetPr(array_ptr, arr1);

don't do what you probably think they do.  At least not in the
commercial product from TMW.  In particular, the mxSetPr() function call
is incorrect.  One uses function mxSetPr() to *replace* an existing
mxArray's entire (real) data array.  This, among other things, means
that the array passed as the second parameter to mxSetPr() *must* be
dynamically allocated--often through mxMalloc() or similar.  Otherwise
you have undefined behaviour once the (stack-allocated) 'arr1' goes out
of scope.  You also get a memory leak because mxSetPr() does not free
the memory of the data array it replaces.

I *think* you probably want to do something like this instead

        /* Create and fill 'arr1' as before */
        
        /* Create an mxArray */
        array_ptr = mxCreateDoubleMatrix(1, 5, mxREAL);
        
        /* Initialise the mxArray data values */
        memcpy(mxGetPr(array_ptr), arr1, sizeof arr1);

but whether or not this improves the overall situation with respect to
mexPutVariable() I have no idea.

By the way, this discussion is very nearly off-topic as far as I can
tell.


Sincerely
-- 
Bård Skaflestad <address@hidden>