Are Fortran mex files restricted to fixed format?

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Josh G.
Josh G. on 28 Mar 2019
Commented: Josh G. on 8 Apr 2019
I'm learning to mex Fortran files and am having trouble with the timestwo.F tutorial. I'm able to compile and run the built-in, fixed format example file without a problem. However, when I tried to compile my own free format file named timestwo.f90, I got a bunch of errors about invalid preprocessor directives.
From a MATLAB Answers question, I found that I needed to capitalize the f in the file extension. mex timestwo.F90 completes successfully. When I try to use the function, though, I get an error:
Invalid MEX-file '/home/user/Documents/MATLAB/mex/timestwo.mexa64': /home/user/Documents/MATLAB/mex/timestwo.mexa64: undefined
symbol: mxgetdoubles_
The only difference between my file and the example file is that mine is free format and doesn't include the #if MX_HAS_INTERLEAVED_COMPLEX check found in the example file. Is this an issue with support for free format source?

Answers (1)

Josh G.
Josh G. on 28 Mar 2019
I figured this out a few minutes after posting my question by trying something I thought I had already tried: adding the -R2018a option. My guess is I had to both add -R2018a to the mex options and change the file extension to .F90, which I had probably tried individually but not simultaneously. I'll leave the question up in case someone has this same problem in the future when getting into using Fortran mex files.
  2 Comments
Josh G.
Josh G. on 8 Apr 2019
Using the -R2018a option was why my code started working, but you're right that it has nothing to do with formatting.
It turns out mxGetDoubles was introduced in R2018b; you have to use mxGetPr for pre-R2018b compatibility.
I'm on Linux, so fortunately I don't have a fixed format flag built into the gfortran mexopts file, but over the past week I've had to work on a Windows system a good bit and have had to deal with repeatedly removing the /fixed flag while resetting the compiler configuration. It's beyond me why they would include that when it doesn't cause any problems to remove it.

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