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Re: Problems using MathLink

  • To: mathgroup at smc.vnet.net
  • Subject: [mg95316] Re: Problems using MathLink
  • From: Steve Wilson <stevew at wolfram.com>
  • Date: Thu, 15 Jan 2009 06:11:37 -0500 (EST)
  • References: <gkgq0p$48v$1@smc.vnet.net> <200901141031.FAA17019@smc.vnet.net> <A6D29BB9-24ED-4F10-90C5-F86B4A92DFD3@wolfram.com> <496E545D.8080306@informatik.uni-leipzig.de>

Yes, you need to call delete[] for the dims array.


On Jan 14, 2009, at 2:08 PM, Jens-Peer Kuska wrote:

> Hi,
>
> you also not free the memory !
>
> void rot(MLINK link, double theta)
> {
>
> /*
> Because the original function was only sending Heads of type List,
> We can simply pass MLPutRealArray a NULL pointer for the heads
> argument and MathLink will send the head List for each level of the  
> array.
> */
>
> double a[3][3];
> a[0][0] = cos(theta);    a[0][1] = sin(theta);   a[0][2] = 0;
> a[1][0] = - sin(theta);  a[1][1] = cos(theta);  a[1][2] = 0;
> a[2][0] = 0;                 a[2][1] = 0;               a[2][2] = 1;
>
> long *dims, depth;
>
> /*
> The array is only depth 2.  The original version told MLPutRealArray  
> that
> the data array 'a' had a depth of 3.   MLPutRealArray tried to send  
> the extra dimension
> which didn't actually exist which lead to the crash.
> */
>
> dims = new long[2];
> dims[0] = 3;  dims[1] = 3;
> MLPutRealArray(link, *a, dims, (char **)0, 2);
>
> /*************************************************
> because otherwise, every call waste 32 byte of heap memory
>  ************************************************/
> delete[] dims;
> }
>
> Regards
> Jens
>
> Steve Wilson wrote:
>> Here are the modifications that this function needs in order to  
>> work correctly:
>>
>> void rot(MLINK link, double theta)
>> {
>>
>> /*
>> Because the original function was only sending Heads of type List,
>> We can simply pass MLPutRealArray a NULL pointer for the heads
>> argument and MathLink will send the head List for each level of the  
>> array.
>> */
>>
>> double a[3][3];
>> a[0][0] = cos(theta);
>> a[0][1] = sin(theta);
>> a[0][2] = 0;
>> a[1][0] = - sin(theta);
>> a[1][1] = cos(theta);
>> a[1][2] = 0;
>> a[2][0] = 0;
>> a[2][1] = 0;
>> a[2][2] = 1;
>>
>> long *dims, depth;
>>
>> /*
>> The array is only depth 2.  The original version told  
>> MLPutRealArray that
>> the data array 'a' had a depth of 3.   MLPutRealArray tried to send  
>> the extra dimension
>> which didn't actually exist which lead to the crash.
>> */
>>
>> dims = new long[2];
>> dims[0] = 3;
>> dims[1] = 3;
>> MLPutRealArray(link, *a, dims, (char **)0, 2);
>> }
>>
>>
>> Steve Wilson
>> Senior Network/System Protocol Developer
>> Wolfram Research, Inc.
>>
>>
>> On Jan 14, 2009, at 3:31 AM, Jens-Peer Kuska wrote:
>>
>>> Hi,
>>>
>>> you are sure that your array has the depth 3 and not
>>> the dimension 3 x 3, and what is the third dimension
>>> in a[3][3] ..
>>>
>>> BTW, you never delete[] heads,dims.
>>> If you wish to fill your main memory you should
>>> use larger pieces of memory
>>> that you don't recycle, you are faster done than.
>>>
>>> Regards
>>>  Jens
>>>
>>> Jonathan Yik wrote:
>>>> Hi,
>>>>
>>>> I'm trying to write a subroutine in C++ that passes a rotation  
>>>> matrix to
>>>> Mathematica through MathLink.  The code compiles fine, but when I  
>>>> try to run
>>>> the compiled program, I get a segfault at the point in the  
>>>> program where the
>>>> subroutine is called.  As far as I can tell, the fault occurs  
>>>> whenever the
>>>> program calls MLPutRealArray or MLPutReal32Array.
>>>>
>>>> Here is my code for the subroutine:
>>>>
>>>> void rot(MLINK link, double theta)
>>>> {
>>>> char **heads, **HEAD;
>>>> heads = new char*[3];
>>>> heads[0] = "List";
>>>> heads[1] = "List";
>>>> heads[2] = "List";
>>>> double a[3][3], *b;
>>>> a[0][0] = cos(theta);
>>>> a[0][1] = sin(theta);
>>>> a[0][2] = 0;
>>>> a[1][0] = - sin(theta);
>>>> a[1][1] = cos(theta);
>>>> a[1][2] = 0;
>>>> a[2][0] = 0;
>>>> a[2][1] = 0;
>>>> a[2][2] = 1;
>>>> long *dims, *D, depth;
>>>> dims = new long[3];
>>>> dims[0] = 3;
>>>> dims[1] = 3;
>>>> dims[2] = 3;
>>>> MLPutRealArray(link, *a, dims, heads, 3);
>>>> }
>>>>
>>>> Is there something in this code that I'm missing that causes the  
>>>> fault?  Or
>>>> is this a but in the ml32i3.dll file?
>>>>
>>>> Yours,
>>>>
>>>> Johnathan Yik
>>
>>



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