MATLAB: Am I unable to compile the “timestwo” Fortran-MEX documentation example in MATLAB

buildfortranMATLABmex

I have saved the timestwo.F example in the documentation as timestwo.f on my system. This is the example located in $MATLAB\extern\examples\refbook, (where $MATLAB is the MATLAB root directory on your machine, as returned by typing
   matlabroot  at the MATLAB command prompt.
When I compile timestwo.f, I receive the following errors:
 timestwo.f:22: 
          mwpointer plhs(*), prhs(*)
          1              2
 Unrecognized statement name at (1) and invalid form for assignment or statement-function definition at (2)
 timestwo.f:23: 
          mwpointer mxGetPr, mxCreateDoubleMatrix
          1                2
 Unrecognized statement name at (1) and invalid form for assignment or statement-function definition at (2)
 timestwo.f:24: 
          mwpointer x_pr, y_pr
          1             2
 Unrecognized statement name at (1) and invalid form for assignment or statement-function definition at (2)
 timestwo.f:18: 
          subroutine mexFunction(nlhs, plhs, nrhs, prhs)
                                       1
 timestwo.f:51: (continued):
          plhs(1) = mxCreateDoubleMatrix(m,n,0)
          2
 Invalid declaration of or reference to symbol `plhs' at (2) [initially seen at (1)]
 timestwo.f:52: warning:
          x_pr = mxGetPr(prhs(1))
                 1
 timestwo.f:53: (continued):
          y_pr = mxGetPr(plhs(1))
                 2
 Argument #1 of `mxgetpr' is one type at (2) but is some other type at (1) [info -f g77 M GLOBALS]
     mex: compile of 'timestwo.f' failed.
 ??? Error using ==> mex
 Unable to complete successfully

Best Answer

The reason for the compilation errors is that the original timestwo.F file contains preprocessor directives and #include statements that need to be processed by a preprocessor. When the Fortran file is renamed with a ".f" extension, the C preprocessor is not invoked and the preprocessor directives are not recognized, thus causing these errors. To compile the file successfully, first rename the file to timestwo.F.
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