Free Pascal Calling Silverfrost FORTRAN

Free Pascal is a 32, 64 and 16 bit compiler for multiple hardware platforms (Intel x86, AMD64/x86-64, PowerPC, PowerPC64, SPARC) and operating systems (DOS, Win32, Win64, Linux, FreeBSD, Mac OS X/iOS/Darwin, OS/2). testsubs.pas is an extremely simple command console program that calls FORTRAN SUBROUTINE QUADROOT (...) (solves quadratic equation) in mathproc.dll.  It was tested in Compiler modes (Options, Compiler, Compiler mode) Free Pascal dialect and Delphi compatible.  Compile as 32-bit for compatibility with Silverfrost Plato IDE compiled mathproc.dll.  Program testsubs executes in a MS-DOS Command Prompt.

The statement

 procedure QUADROOT (VAR A, B, C, ROOT1, ROOT2, DISC: single;
                     VAR IERR: smallint);
                     stdcall; external 'mathproc';
      

defines an external reference to the FORTRAN SUBROUTINE QUADROOT (...) in mathproc.dll (Programmer's Guide Chapter 12).

 FORTRAN converts the identifiers in its symbol table to upper case, therefore the

procedure/subroutine names (QUADROOT) must be in upper case. FORTRAN's default requires its parameters to be passed by reference (can be overridden in an all FORTRAN solution), necessitating the VAR keywords. Define/Pass data as smallint and single to match FORTRAN's INTEGER*2 and REAL data types (see Variable Storage Compatibility and Equivalency). stdcall specifies the calling model.

external 'mathproc' specifies that the procedure/subroutine is in mathproc.dll.  The Free Pascal Compiler/Linker does not require a user supplied
mathproc.lib.  This is all that is needed to link in mathproc.dll's SUBROUTINE QUADROOT (...) during Free Pascal compilation and linkage to
produce an executable.

Calling a FORTRAN SUBROUTINE from Free Pascal is easier than from either Fujitsu COBOL or DMD D.

Arrays

Consider the FORTRAN SUBROUTINE declaration (defined in mathproc.dll) below.  This subroutine takes an array of electrical resistances, R, and calculates/returns an equivalent resistance array for the circuit shown1, RE. Both R and RE are dynamically dimensioned (or dimensioned with variable bounds) for N elements.  The solution at right defines a single statically dimensioned array TYPE resistance, defines RL (resistance array) and re (equivalent resistance array) as that TYPE, loads RL, and calls RSTVLADR01 (...). (iErr is returned error code)

1. Schick, William and Charles J. Mertz, Jr. (1972).  FORTRAN for Engineering.  New York: McGraw-Hill Book Company.