gfortran on MacOS

How to Install a Precompiled Binary Package

A binary package is available as an RPM which can be installed using APT/RPM as

$ sudo apt-get update
$ sudo apt-get install gcc
$ sudo apt-get clean

Notice that this will replace your default gcc compilers (gcc and g++), which is necessary to allow mixed use of C, C++, and FORTRAN for a single application. The default gcc compilers can be switched by using the "altarnatives" command as follows and answering the questions:

$ sudo alternatives --config gcc


 

REMARKS

• The gcc suit including gfortran is not yet officially supported for M1 Macs, so use it at your own risk. Special care must be taken if you want to call fortran subroutines/functions with "character*" arguments from C/C++, since if the number of arguments exceeds a certain threshold, the string lengths are not properly passed to the fortran side, which was the major obstacle I encountered to make cernlib work on my M1 box.
• As a general rule, you should make sure that optimization does not change your results.
• Avoid too many else if's in the same level. You sometimes need to nest them, if the compiler abends.
• gfortran forbids jumping into a different "IF" block.
• gfortran does not initialize a "BLOCK DATA" even if you declare it "EXTERNAL". In order to force it, say "blkdat", initialized, I needed a trick like
  
      external blkdat
      call dummysub(blkdat)
  
  with
      subroutine dummysub(a)
      return
      end
  
  
• gfortran now returns IOSTAT=5002 (instead of IOSTAT=3 as with gcc-4.2 or older), when the EOF is reached for an random access file, which behavior is different from that of g77.
• Here is a sample FCFLAGS I usually use to compile my legacy fortran programs:
  
      FCFLAGS = -fno-automatic -fno-second-underscore -fno-range-check -fallow-argument-mismatch -fallow-invalid-boz -undefined warning