Re: Creating a logical matrix in a mex-file

Christopher Hulbert wrote:

Generate the array using one dimension of 0 or rank 0. This will
not allocate
the data for the array. Then use mxMalloc to allocate the memory
*without*
initialization. Use mxSetData to set the data of the array to the
allocated
memory. This would avoid the initialization of the memory.

Ok. I not quite sure how to do that. For example how do I
transform

int m = 1000;
int n = 1000;
mxArray *A_ptr;
A_ptr = mxCreateLogicalMatrix(m, n);
bool *A;
A = mxGetPr(A_ptr);

into code which does not initialize the elements of A.
My guess would be

int m = 1000;
int n = 1000;
mxArray *A_ptr;
A_ptr = mxMalloc(m*n+2);
mxSetM(A_ptr, m);
mxSetN(A_ptr, n);
bool *A;
A = mxGetPr(A_ptr);

I really have no idea how much memory to allocate. Since there a
differnce between a pointer to an mxArray and a pointer to the data
of an mxArray, and since arrays are stored as vectors, there should
be some extra bytes storing
the dimension and size of the array. Using mxMalloc I would guess I
have to take that into account.
Another unanswered question is whether I am chasing a ghost here
trying to avoid initialization.

Thank you all for your patience and help with my neverending
questions on mex-files.

Fred
.

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