fortran_from_c

Fortran from C

How to call Fortran code from C.

Differences between C and Fortran

• Fortran appends _ to the end of symbol names. See that with readelf -s f.o.

  Therefore, your c code must look for f_ functions.

  There are also -fno-underscore and -fno-second-underscore options to the Fortran compiler.

• Fortran is case insensitive, and symbols are all lowercased.

• Fortran arrays are column-major, c is row-major.

  Fortran memory:

  a(1,1)  a(2,1)  a(1,2)  a(2,2)  a(1,3)  a(2,3)
  

  C memory:

  a[0][0] a[0][1] a[0][2] a[1][0] a[1][1] a[1][2]
  

• Fortran strings contain length. TODO: how?

• Fortran subroutines pass by reference by default.

  Therefore, corresponding C code must use pointers on function declaration.

  Fortran functions however work like C functions.

• You must convert corresponding types correctly to match number of bytes and definition.

  This may be hard, because those values may be compiler/machine dependant.

  Not sure there is a bulletproof way to deal with this.

• You have to link to the Fortran standard library if you want to call functions such as write or abs.

  In my Ubuntu system, it is called libgfortran.so.3.0.0, so locate fortran.so should show you the location.

  You could also find this by asking the dependencies of a regular fortran executable as:

  readelf -d executable.elf
  

Bibliography

• http://owen.sj.ca.us/~rk/howto/FandC/FandC.call.html
• http://www.yolinux.com/TUTORIALS/LinuxTutorialMixingFortranAndC.html