MATLAB: Help with Mex function

mex

Hello, I'm having trouble getting a mex function to work. I think I've narrowed down the problem but anytime I try to fix anything Matlab shuts down.

I want to send a nested struct through a mex file myvar.myfield.mysubfield, where subfield is a 3-d position vector. I want to do mymexfunc(myvar).

mwPointer mxGetField
mwPointer mxGetPr
mwPointer mxcreatedoublematrix
mwIndex index
mwpointer var_ptr, fd_ptr, sfd_ptr
var_ptr = mxgetpr(prhs(1))
fd_ptr = mxgetfield(var_ptr,1,'myfield')
sfd_ptr = mxgetfield(fd_ptr,1,'mysubfield')
myvar%myfield%mysubfield = fpgetpr(sfd_ptr)
copy mxcopyptrtoreal8(sfd_ptr,myvar%myfield%mysubfield,size)

Matlab crashes when I try to do this and I wanted to know if anyone can see what I'm doing wrong.

Best Answer

mwPointer mxGetField
mwPointer mxGetPr
mwPointer mxcreatedoublematrix
mwIndex index
mwpointer var_ptr, fd_ptr, sfd_ptr
fd_ptr = mxgetfield(prhs(1),1,'myfield') ! Result is mxArray pointer
sfd_ptr = mxgetfield(fd_ptr,1,'mysubfield') ! Result is mxArray pointer
var_ptr = mxgetpr(sfd_ptr) ! Result is real*8 pointer
copy mxcopyptrtoreal8(var_ptr,myvar%myfield%mysubfield,size)

I would use different names for the "size" and "index" variables, since those are names of Fortran intrinsic functions.

Related Solutions

MATLAB: Building Mex file with Fortan

Your main problem is that you need to create the output array PLHS(1) before you access it. Also your NLHS and NRHS types are wrong. Try this:

#include <fintrf.h>
C
C Gateway routine
C
    SUBROUTINE MEXFUNCTION(NLHS, PLHS, NRHS, PRHS)
    implicit none
C mexFunction arguments:
    MWPOINTER PLHS(*), PRHS(*)
    INTEGER NLHS, NRHS
    mwPointer, external :: mxGetPr, mxGetPi
    mwPointer, external :: mxCreateDoubleMatrix, mxCreateNumericArray
    mwSize, external :: mxGetM, mxGetN
    MWPOINTER YPP 
    mwSize M, N
    integer*4 ComplexFlag
    REAL *8 RYPP(1)
    RYPP(1) = 10
    M = 1
    N = 1
    ComplexFlag = 0
    PLHS(1) = mxCreateDoubleMatrix( M, N, ComplexFlag )
    YPP = MXGETPR(PLHS(1))
    CALL MXCOPYREAL8TOPTR(RYPP, YPP, M*N)
    RETURN
    END

MATLAB: Mex large output array

You have to combine the data into one array inside the mex routine itself. Once outside the mex routine, if all you have is the y1, y2, etc variables then you will have to manually concatenate them together (which will involve a data copy of course). I am guessing this is possible inside the mex routine with the mxCopyReal8ToPtr function (passing a pointer to the middle of a memory block) but confess I haven't tried it ... you may get an assert fault. If you do get a fault there are ways around it. Let me know if you need help with this.

EDIT

I just ran a test and mxCopyReal8ToPtr does not generate an assert fault if passed an address in the middle of a memory block. So a code snippet example for doing this is:

mwPointer mxCreateDoubleMatrix
mwPointer mxGetPr
    :
mwPointer pr
real*8 x(3), y(3) ! start with two separate Fortran variables
mwSize m, n
integer*4 complexity
    :
x = [1,2,3]
y = [4,5,6]
m = 3
n = 2
complexity = 0
plhs(1) = mxCreateDoubleMatrix(m,n,complexity)
pr = mxGetPr(plhs(1)) ! point to 1st column
call mxCopyReal8ToPtr(x,pr,m) ! copy into the 1st column
pr = pr + m*8 ! pointer arithmetic, point to 2nd column
call mxCopyReal8ToPtr(y,pr,m) ! copy into the 2nd column

Best Answer

Related Solutions

MATLAB: Building Mex file with Fortan

MATLAB: Mex large output array

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