Conventions for XL Fortran external names

• Both the underscore (_) and the dollar sign ($) are valid characters anywhere in names.

  Because names that begin with an underscore are reserved for the names of library routines, do not use an underscore as the first character of a Fortran external name.

  To avoid conflicts between Fortran and non-Fortran function names, you can compile the Fortran program with the -qextname option. This option adds an underscore to the end of the Fortran names. Then use an underscore as the last character of any non-Fortran procedures that you want to call from Fortran.

• Names can be up to 250 characters long.
• Program and symbolic names are interpreted as all lowercase by default. If you are writing new non-Fortran code, use all-lowercase procedure names to simplify calling the procedures from Fortran.
  You can use the -qmixed option or the @PROCESS MIXED directive if you want the names to use both uppercase and lowercase:

  @process mixed
         external C_Func    ! With MIXED, we can call C_Func, not just c_func.
         integer aBc, ABC   ! With MIXED, these are different variables.
         common /xYz/ aBc   ! The same applies to the common block names.
         common /XYZ/ ABC   ! xYz and XYZ are external names that are
                            ! visible during linking.
         end

• Names for module procedures are formed by concatenating __ (two underscores), the module name, _IMOD_ (for intrinsic modules) or _NMOD_ (for non-intrinsic modules), and the name of the module procedure. For example, module procedure MYPROC in module MYMOD has the external name __mymod_NMOD_myproc.
  Note: Symbolic debuggers and other tools should account for this naming scheme when debugging XL Fortran programs that contain module procedures. For example, some debuggers default to lowercase for program and symbolic names. This behavior should be changed to use mixed case when debugging XL Fortran programs with module procedures.
• The XL compilers generate code that uses main as an external entry point name. You can only use main as an external name in these contexts:
  • A Fortran program or local-variable name. (This restriction means that you cannot use main as a binding label, or for the name of an external function, external subroutine, block data program unit, or common block. References to such an object use the compiler-generated main instead of your own.)
  • The name of the top-level main function in a C program.
• Some other potential naming conflicts may occur when linking a program. For instructions on avoiding them, see Linking new objects with existing ones and Avoiding naming conflicts during linking in the XL Fortran Compiler Reference.

  xlf90 -brename:old_name,new_name interlanguage_calls.f