passing a structure into a fortran subroutine in a mex file.

Hi, I am trying to pass a matlab structure into a fortran subroutine using mex files. I am not sure how to do that since I need to convert the matlab structure into a fortran data type. I was wondering if anyone can help with showing a simple example of passing a matlab structure into a fortran subroutine.

Thanks

Answer 1

[James Tursa]

You will have to copy the data one field at a time. This is true for both passing in a structure and passing out a structure, primarily because of the fact that the MATLAB data is not contiguous in memory whereas the Fortran data most likely will need to be contiguous. I don't have a Fortran compiler handy to test any of the following, but the process would look something like this for known field sizes (CAUTION, this is a bare bones outline with no argument checking and untested):

MATLAB m-code:

myStruct.scalar = 5;
myStruct.vector = [1 2 3];
myStruct.matrix = [1 2;3 4];
myMexRoutine(myStruct);

Fortran code for myMexRoutine:

#include "fintrf.h"
      subroutine mexFunction(nlhs, plhs, nrhs, prhs)
      implicit none
      integer nlhs, nrhs
      mwPointer plhs(*), prhs(*)
!-FUN
      mwPointer, external :: mxGetField
      real*8, external :: mxGetPr
!-LOC
      TYPE FortranStruct
          REAL*8 scalar
          REAL*8 vector(3)
          REAL*8 matrix(2,2)
      end type FortranStruct
      TYPE(FortranStruct) myStruct
      mwPointer field
      mwPointer pr
      mwSize n
      mwIndex :: i = 0
!-----
      field = mxGetField(prhs(1),i,"scalar")
      pr = mxGetPr(field)
      n = 1
      call mxCopyPtrToReal8(pr, myStruct%scalar, n)

        field = mxGetField(prhs(1),i,"vector")
        pr = mxGetPr(field)
        n = 3
        call mxCopyPtrToReal8(pr, myStruct%vector, n)

        field = mxGetField(prhs(1),i,"matrix")
        pr = mxGetPr(field)
        n = 4
        call mxCopyPtrToReal8(pr, myStruct%matrix, n)

And if you wanted to pass out a structure you would need to do data copies in the reverse direction.

[Michael Loibl]

I am actually trying the reverse direction (having a structure as an output). Unfortunately, I don't find I way to make it work. Can somebody help?

[James Tursa]

@Michael Loibl Please post a new Question, with a small example of what you have on the Fortran side and what you want on the MATLAB side.

[Michael Loibl]

I actually found an answer for myself in the meantime. But thank you for the reply.