Mex files crashes when run

Hi. I have written and compiled a mex file from a Fortran source code. However, I have problems running it as Matlab crashes whenever I run the mex file. Can anybody find out where is the problem?

My fortran source code is as follows.

#include "fintrf.h"
C======================================================================
#if 0
C     
C     add.F
C    .F file needs to be preprocessed to generate .for equivalent
C     
#endif
C     
C     add.f
C
C     Adds two integers
C   
C======================================================================
C     Gateway routine
      subroutine mexFunction(nlhs, plhs, nrhs, prhs)

C     Declarations
      implicit none

C     mexFunction arguments:
      mwPointer plhs(*), prhs(*)
      integer nlhs, nrhs

C     Pointers to input/output mxArrays:
      mwPointer a, b
      mwPointer c

C     Function Declerations
      mwPointer mxGetData

        a = mxGetData(prhs(1))
        b = mxGetData(prhs(2))
        c = mxGetData(plhs(1))

C     Call the computational subroutine.
      call add(%val(a), %val(b), %val(c))

        return
        end
  C-----------------------------------------------------------------------
  C     Computational subroutine
        subroutine add(a, b, c)

        integer*8 a, b, c

        c = a + b

        return
        end

Answer 1

[James Tursa]

The main problem is that you, the programmer, need to create the output mxArray plhs(1). When you run the mex routine the only mxArray variables you start with are the prhs(etc) variables. At that point in the code, prhs(1) is unallocated. MATLAB does not create the plhs(etc) outputs for you since it does not know what the output is supposed to be ... that is your job as the programmer. Also, you should check that the inputs are int64 type before you use them that way. E.g.,

C     Gateway routine
      subroutine mexFunction(nlhs, plhs, nrhs, prhs)

C     Declarations
      implicit none

C     mexFunction arguments:
      mwPointer plhs(*), prhs(*)
      integer nlhs, nrhs

C     Pointers to input/output mxArrays:
      mwPointer a, b
      mwPointer c

C     Function Declerations
      mwPointer mxGetData

          integer*4, external :: mxClassIDFromClassName
          integer*4, external :: mxIsInt64
          mwPointer, external :: mxGetNumberOfElements
          mwPointer, external :: mxCreateNumericMatrix
          mwSize :: one = 1
          integer*4 :: mxREAL = 0
          integer*4 classid
          if( nrhs /= 2 .or. nlhs > 1 ) then
            call mexErrMsgTxt("Need 2 inputs and at most 1 output")
          endif
          if( mxIsInt64(prhs(1))==0 .or. mxIsInt64(prhs(2))==0 ) then
            call mexErrMsgTxt("Inputs must be int64 class")
          endif
          if( mxGetNumberOfElements(prhs(1)) /= 1 .or.
       &      mxGetNumberOfElements(prhs(2)) /= 1 ) then
            call mexErrMsgTxt("Inputs must be scalar")
          endif
          classid = mxClassIDFromClassName("int64")
          plhs(1) = mxCreateNumericMatrix(one,one,classid,mxREAL)
          a = mxGetData(prhs(1))
          b = mxGetData(prhs(2))
          c = mxGetData(plhs(1))

C     Call the computational subroutine.
      call add(%val(a), %val(b), %val(c))

          return
          end
    C-----------------------------------------------------------------------
    C     Computational subroutine
          subroutine add(a, b, c)

          integer*8 a, b, c

          c = a + b

          return
          end