Re: Problems using MathLink

*To*: mathgroup at smc.vnet.net*Subject*: [mg95309] Re: Problems using MathLink*From*: Steve Wilson <stevew at wolfram.com>*Date*: Thu, 15 Jan 2009 06:10:17 -0500 (EST)*References*: <gkgq0p$48v$1@smc.vnet.net> <200901141031.FAA17019@smc.vnet.net>

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