MATLAB mex c + Fortran Error

Question

I'm trying to mex a project made up of files written in c and fortran. In order to make it easy I created this simple funcions:

mysum.f

  SUBROUTINE mysum(a,b)
  REAL :: a,b,r

  r = a+b
  WRITE(*,*) r
  END SUBROUTINE mysum

and test.c

#include <mex.h>
#include <stdio.h>

extern void mysum(double *a, double *b);
double a,b;

void mexFunction(int nlhs, mxArray *plhs[], int nrhs, const mxArray *prhs[]){

a   =(double) mxGetScalar(prhs[0]);
b   =(double) mxGetScalar(prhs[1]);

mysum(&a,&b);

return;
}

With Intel Fortran Compiler (x64) I run:

ifort /c mysum.f

and it creates mysum.obj

In Matlab (x64) I'm using Microsoft SDK as compiler and I write:

mex -O -largeArrayDims LINKFLAGS="$LINKFLAGS /NODEFAULTLIB:MSVCRT.lib" test.c mysum.obj

Unfortunatelly it gives this error:

test.obj : error LNK2019: unresolved external symbol mysum referenced in function mexFunction test.mexw64 : fatal error LNK1120: 1 unresolved externals

At this point I'm stuck and I don't know what to do. I'm using the option /NODEFAULTLIB because there was a conflict otherwise with MSVCRT.lib.

I need some help please.

score 1 · Accepted Answer · edited May 23 '17 at 11:56

1

Or in the Fortran you can use the ISO C Binding and specify the names by which Fortran procedures will be seen by other languages and the linker, specifying case and not needing underscores. You can also declare variables so that compatibility with C is guaranteed. In your example, Fortran default real and C double probably don't match. See https://stackoverflow.com/questions/tagged/fortran-iso-c-binding or the gfortran manual (its part of the language standard and so the documentation there is more generally applicable). For this example:

SUBROUTINE mysum(a,b) bind ( C, name = "mysum" )
use iso_c_binding
implicit none
REAL (c_double) :: a,b,r

r = a+b
WRITE(*,*) r
END SUBROUTINE mysum

edited May 23 '17 at 11:56

Community

1
1

answered Sep 14 '13 at 04:59

M. S. B.

28,968
2
46
73

Note that the `iso_c_binding` module is only available on Fortran 2003 and later. `mysum.f` is pre-Fortran 90/95... It might depend on the compiler whether it accepts the code. Better use `mysum.F90` when using the module. – Alexander Vogt Sep 14 '13 at 08:52
Fixed form source is valid Fortran 2008, there is no reason for compiler to have problems. Also, the capital F would mean that C preprocesor should be used. – Vladimir F Героям слава Sep 15 '13 at 07:17

score 0 · Answer 2 · answered Sep 13 '13 at 17:43

0

You probably need to append an underscore to mysum in the C code:

extern void mysum_(double *a, double *b);

void mexFunction(int nlhs, mxArray *plhs[], int nrhs, const mxArray *prhs[]){
//...
  mysum_(&a,&b);
//...
}

Run nm mysum.obj to get the correct names for all subroutines.

answered Sep 13 '13 at 17:43

Alexander Vogt

17,879
13
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I'm using Windows and cannot run the command. The compiler help said that it should be without underscore. I tried with the underscore and it didn't work. Binding resolved the problem. thx – user2279697 Sep 14 '13 at 17:53

MATLAB mex c + Fortran Error

2 Answers2