MATLAB: MATLAB encountered an internal error and needs to close -MEX file

crashfortran mex fileMATLAB Compiler

I debugged my code based on Mathwork post https://www.mathworks.com/help/matlab/matlab_external/debugging-on-microsoft-windows-platforms.html and crashed MATLAB. This my code:
#include "fintrf.h"
        subroutine mexFunction(nlhs, plhs, nrhs, prhs) ! Interface 
        IMPLICIT REAL*8(A-H,O-Z)
        mwpointer plhs(*), prhs(*)
  C      integer nlhs, nrhs
        mwpointer mxCreateDoubleMatrix, mxGetPr
        double precision mxGetScalar
C     Pointers to input/output mxArrays:
      mwPointer TT
C     Get the size of the input array.
      m_in = 20
      n_in = 1
      size = m_in * n_in
C     Create Fortran array from the input argument.
C        IZ  = mxGetScalar(prhs(1));
C        EEAR = mxGetScalar(prhs(2));
C        DDIA = mxGetScalar(prhs(3));
C        RRPM = mxGetScalar(prhs(4));
        NN  = mxGetScalar(prhs(1));
C     Create matrix for the return argument.
      plhs(1) = mxCreateDoubleMatrix(m_in, n_in, 0)
      TT = mxGetPr(plhs(1))
        call LOOPS1(%VAL(TT),%VAL(NN)) ! call the computation
        return
        end
        subroutine LOOPS1(TT, nn)
        IMPLICIT REAL*8(A-H,O-Z)
        n1 = nn+1
        call LOOPS(TT, n1)
        return
        end
The error is in the line (n1 = nn+1). I don't know what the problem is. Please help me.

Best Answer

Some comments:
----------------------------------------------------------------------------------------
        IMPLICIT REAL*8(A-H,O-Z)
You need to delete this from your brain and never use it again. Ever. One of the few helps you get with a Fortran compiler for spotting typing issues and variable name misspellings etc is with the following, so use it in all of your code from now on:
        IMPLICIT NONE
This will force you to type everything, but it is worth it in the long run.
----------------------------------------------------------------------------------------
C      integer nlhs, nrhs
Which means of course you will need to uncomment this line (as well as add typing statements for all of your other untyped variables).
----------------------------------------------------------------------------------------
      m_in = 20
      n_in = 1
         :
      plhs(1) = mxCreateDoubleMatrix(m_in, n_in, 0)
Unlike C/C++, you do not get automatic argument promotion in Fortran ... especially for implicit interfaces. So you should always use the exact types specified in the documented signature and never use explicit constants in argument lists. E.g., the signature for mxCreateDoubleMatrix is:
mwPointer mxCreateDoubleMatrix(m, n, ComplexFlag)
mwSize m, n
integer*4 ComplexFlag
So your code should follow this signature exactly. E.g.,
      mwSize m_in, n_in
      integer*4 :: ComplexFlag = 0
          :
      m_in = 20
      n_in = 1
         :
      plhs(1) = mxCreateDoubleMatrix(m_in, n_in, ComplexFlag)
----------------------------------------------------------------------------------------
      size = m_in * n_in
size is the name of an intrinsic function in Fortran. You should pick a different name for your variable.
----------------------------------------------------------------------------------------
        call LOOPS1(%VAL(TT),%VAL(NN)) ! call the computation
TT is holding a pointer value, but NN is just an integer variable (not holding a pointer to a integer variable). So you should not be passing NN by value here (this error is what is causing your crash). E.g., you should be doing this instead:
        call LOOPS1(%VAL(TT),NN) ! call the computation
----------------------------------------------------------------------------------------
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