# cfortran.h: Interfacing C or C++ and FORTRAN

Author: Burkhard Burow
Email: burow@desy.de
www: www-zeus.desy.de/~burow/cfortran

Supports:

              Alpha and VAX VMS, Alpha OSF, DECstation and VAX Ultrix, IBM RS/6000,
              Silicon Graphics, Sun, CRAY, Apollo, HP9000, LynxOS, Convex, Absoft,
              f2c, g77, NAG f90, PowerStation FORTRAN with Visual C++, NEC SX-4,
              Portland Group.

C and C++ are generally equivalent as far as `cfortran.h` is concerned. Unless explicitly noted otherwise, mention of C implicitly includes C++. C++ compilers tested include:

      SunOS> CC +p +w      # Clean compiles.
      IRIX>  CC            # Clean compiles.
      IRIX>  CC -fullwarn  # Still some warnings to be overcome.
      GNU>   g++ -Wall     # Compiles are clean, other than warnings for unused
                           #   cfortran.h static routines.

N.B.: The best documentation on interfacing C or C++ and FORTRAN is in the chapter named something like 'Interfacing C and FORTRAN' to be found in the user's guide of almost every FORTRAN compiler. Understanding this information for one or more FORTRAN compilers greatly clarifies the aims and actions of `cfortran.h`. Such a chapter generally also addresses issues orthogonal to `cfortran.h`, for example the order of array indices, the index of the first element, as well as compiling and linking issues.

## Short Summary of the Syntax Required to Create the Interface

e.g. Prototyping a FORTRAN subroutine for C: `PROTOCCALLSFSUBni` is optional for C, but mandatory for C++.

                     PROTOCCALLSFSUB2(SUB_NAME,sub_name,STRING,PINT)
    #define SUB_NAME(A,B) CCALLSFSUB2(SUB_NAME,sub_name,STRING,PINT, A,B)

                                    ^     -                                       -
           number of arguments _____|    |   STRING   BYTE    PBYTE       BYTEV(..)|
                                      /  |   STRINGV  DOUBLE  PDOUBLE   DOUBLEV(..)|
                                     /   |  PSTRING   FLOAT   PFLOAT     FLOATV(..)|
            types of arguments ____ /    | PNSTRING   INT     PINT         INTV(..)|
                                    \    | PPSTRING   LOGICAL PLOGICAL LOGICALV(..)|
                                     \   |  PSTRINGV  LONG    PLONG       LONGV(..)|
                                      \  |   ZTRINGV  SHORT   PSHORT     SHORTV(..)|
                                         |  PZTRINGV  ROUTINE PVOID      SIMPLE    |
                                          -                                       -

e.g. Prototyping a FORTRAN function for C:

    /* PROTOCCALLSFFUNn is mandatory for both C and C++. */
    PROTOCCALLSFFUN1(INT,FUN_NAME,fun_name,STRING)
    #define FUN_NAME(A)  CCALLSFFUN1(FUN_NAME,fun_name,STRING, A)

e.g. calling `FUN_NAME` from C:

        {int a; a = FUN_NAME("hello");}

e.g. Creating a FORTRAN-callable wrapper for a C function returning void, with a 7 dimensional integer array argument: [Not supported from C++.]

    FCALLSCSUB1(csub_name,CSUB_NAME,csub_name,INTVVVVVVV)

e.g. Creating a FORTRAN-callable wrapper for other C functions:

    FCALLSCFUN1(STRING,cfun_name,CFUN_NAME,cfun_name,INT)
               [ ^-- BYTE, DOUBLE, FLOAT, INT, LOGICAL, LONG, SHORT, VOID
                 are other types returned by functions.       ]

e.g. COMMON BLOCKs:

    FORTRAN:

                             common /fcb/  v,w,x
                                     character *(13) v, w(4), x(3,2)

    C:

    typedef struct { char v[13],w[4][13],x[2][3][13]; } FCB_DEF;
    #define FCB COMMON_BLOCK(FCB,fcb)
    COMMON_BLOCK_DEF(FCB_DEF,FCB);
    FCB_DEF FCB;    /* Define, i.e. allocate memory, in exactly one *.c file. */

e.g. accessing `FCB` in C:

              printf("%.13s",FCB.v);

## I) Introduction

`cfortran.h` is an easy-to-use powerful bridge between C and FORTRAN. It provides a completely transparent, machine independent interface between C and FORTRAN routines (= subroutines and/or functions) and global data, i.e. structures and COMMON blocks.

The complete `cfortran.h` package consists of 4 files: the documentation in cfortran.doc, the engine `cfortran.h`, examples in `cfortest.c` and `cfortex.f`/or. [`cfortex.for` under VMS, `cfortex.f` on other machines.]

The `cfortran.h` package continues to be developed. The most recent version is available via WWW at `http://www-zeus.desy.de/~burow/cfortran`.

The examples may be run using one of the following sets of instructions:

N.B. Unlike earlier versions, `cfortran.h` 3.0 and later versions automatically uses the correct `ANSI ##` or `pre-ANSI /**/` preprocessor operator as required by the C compiler.

N.B. As a general rule when trying to determine how to link C and FORTRAN, link a trivial FORTRAN program using the FORTRAN compilers verbose option, in order to see how the FORTRAN compiler drives the linker. e.g.

           unix> cat f.f
                    END
           unix> f77 -v f.f
           .. lots of info. follows ...

N.B. If using a C `main()`, i.e. FORTRAN `PROGRAM` is not entry of the executable, and if the link bombs with a complaint about a missing "`MAIN`" (e.g. `MAIN__`, `MAIN_`, `f90_main` or similar), then FORTRAN has hijacked the entry point to the executable and wishes to call the rest of the executable via "`MAIN`". This can usually be satisfied by doing e.g. '`cc -Dmain=MAIN__ ...`' but often kills the command line arguments in `argv` and `argc`. The `f77` verbose option, usually `-v`, may point to a solution.

    RS/6000> # Users are strongly urged to use f77 -qextname and cc -Dextname
    RS/6000> # Use -Dextname=extname if extname is a symbol used in the C code.
    RS/6000> xlf -c -qextname cfortex.f
    RS/6000> cc  -c -Dextname cfortest.c
    RS/6000> xlf -o cfortest cfortest.o cfortex.o && cfortest

    DECFortran> #Only DECstations with DECFortran for Ultrix RISC Systems.
    DECFortran> cc -c -DDECFortran cfortest.c
    DECFortran> f77 -o cfortest cfortest.o cfortex.f  &&  cfortest

    IRIX xxxxxx 5.2 02282015 IP20 mips
    MIPS> # DECstations and Silicon Graphics using the MIPS compilers.
    MIPS> cc -o cfortest cfortest.c cfortex.f -lI77 -lU77 -lF77  &&  cfortest
    MIPS> # Can also let f77 drive linking, e.g.
    MIPS> cc -c cfortest.c
    MIPS> f77 -o cfortest cfortest.o cfortex.f  &&  cfortest

    Apollo> # Some 'C compiler 68K Rev6.8' break. [See Section II o) Notes: Apollo]
    Apollo> f77 -c cfortex.f && cc -o cfortest cfortest.c cfortex.o  &&  cfortest

    VMS> define lnk$library sys$library:vaxcrtl
    VMS> cc cfortest.c
    VMS> fortran cfortex.for
    VMS> link/exec=cfortest cfortest,cfortex
    VMS> run cfortest

    OSF1 xxxxxx V3.0 347 alpha
    Alpha/OSF> # Probably better to let cc drive linking, e.g.
    Alpha/OSF> f77 -c cfortex.f
    Alpha/OSF> cc  -o cfortest cfortest.c cfortex.o -lUfor -lfor -lFutil -lots -lm
    Alpha/OSF> cfortest
    Alpha/OSF> # Else may need 'cc -Dmain=MAIN__' to let f77 drive linking.

    Sun> # Some old cc(1) need a little help. [See Section II o) Notes: Sun]
    Sun> f77 -o cfortest cfortest.c cfortex.f -lc -lm  &&  cfortest
    Sun> # Some older f77 may require 'cc -Dmain=MAIN_'.

    CRAY> cft77 cfortex.f
    CRAY> cc -c cfortest.c
    CRAY> segldr -o cfortest.e cfortest.o cfortex.o
    CRAY> ./cfortest.e

    NEC> cc -c -Xa cfortest.c
    NEC> f77 -o cfortest cfortest.o cfortex.f  &&  cfortest

    VAX/Ultrix/cc> # For cc on VAX Ultrix only, do the following once to cfortran.h.
    VAX/Ultrix/cc> mv cfortran.h cftmp.h && grep -v "^#pragma" cfortran.h

    VAX/Ultrix/f77> # In the following, 'CC' is either 'cc' or 'gcc -ansi'. NOT'vcc'
    VAX/Ultrix/f77> CC -c -Dmain=MAIN_ cfortest.c
    VAX/Ultrix/f77> f77 -o cfortest cfortex.f cfortest.o  &&  cfortest

    LynxOS> # In the following, 'CC' is either 'cc' or 'gcc -ansi'.
    LynxOS> # Unfortunately cc is easily overwhelmed by cfortran.h,
    LynxOS> #  and won't compile some of the cfortest.c demos.
    LynxOS> f2c -R cfortex.f
    LynxOS> CC -Dlynx -o cfortest cfortest.c cfortex.c -lf2c  &&  cfortest

    HP9000> # Tested with HP-UX 7.05 B 9000/380 and with A.08.07 A 9000/730
    HP9000> # CC may be either 'c89 -Aa' or 'cc -Aa'
    HP9000> #    Depending on the compiler version, you may need to include the
    HP9000> #    option '-tp,/lib/cpp' or worse, you'll have to stick to the K&R C.
    HP9000> #    [See Section II o) Notes: HP9000]
    HP9000> # Users are strongly urged to use f77 +ppu and cc -Dextname
    HP9000> # Use -Dextname=extname if extname is a symbol used in the C code.
    HP9000> CC  -Dextname -c cfortest.c
    HP9000> f77 +ppu         cfortex.f  -o cfortest cfortest.o && cfortest
    HP9000> # Older f77 may need
    HP9000> f77 -c cfortex.f
    HP9000> CC -o cfortest cfortest.c cfortex.o -lI77 -lF77 && cfortest

    HP0000> # If old-style f77 +800 compiled objects are required:
    HP9000> # #define hpuxFortran800
    HP9000> cc -c -Aa -DhpuxFortran800 cfortest.c
    HP9000> f77 +800 -o cfortest cfortest.o cfortex.f

    f2c> # In the following, 'CC' is any C compiler.
    f2c> f2c -R cfortex.f
    f2c> CC -o cfortest -Df2cFortran cfortest.c cfortex.c -lf2c  &&  cfortest

    Portland Group $ # Presumably other C compilers also work.
    Portland Group $ pgcc -DpgiFortran -c cfortest.c
    Portland Group $ pgf77 -o cfortest cfortex.f cfortest.o && cfortest

    NAGf90> # cfortex.f is distributed with FORTRAN 77 style comments.
    NAGf90> # To convert to f90 style comments do the following once to cfortex.f:
    NAGf90> mv cfortex.f cf_temp.f && sed 's/^C/\!/g' cf_temp.f > cfortex.f
    NAGf90> # In the following, 'CC' is any C compiler.
    NAGf90> CC -c -DNAGf90Fortran cfortest.c
    NAGf90> f90 -o cfortest cfortest.o cfortex.f &&  cfortest

    PC> # On a PC with PowerStation FORTRAN and Visual_C++
    PC> cl /c cftest.c
    PC> fl32  cftest.obj cftex.for

    GNU> # GNU FORTRAN
    GNU> # See Section VI caveat on using 'gcc -traditional'.
    GNU> gcc -ansi -Wall -O -c -Df2cFortran cfortest.c
    GNU> g77 -ff2c -o cfortest cfortest.o cfortex.f &&  cfortest

    AbsoftUNIX> # Absoft FORTRAN for all UNIX based operating systems.
    AbsoftUNIX> # e.g. Linux or Next on Intel or Motorola68000.
    AbsoftUNIX> # Absoft f77 -k allows FORTRAN routines to be safely called from C.
    AbsoftUNIX> gcc -ansi -Wall -O -c -DAbsoftUNIXFortran cfortest.c
    AbsoftUNIX> f77 -k -o cfortest cfortest.o cfortex.f && cfortest

    AbsoftPro> # Absoft Pro FORTRAN for MacOS
    AbsoftPro> # Use #define AbsoftProFortran

    CLIPPER> # INTERGRAPH CLIX using CLIPPER C and FORTRAN compilers.
    CLIPPER> # N.B. - User, not cfortran.h, is responsible for
    CLIPPER> #        f77initio() and f77uninitio() if required.
    CLIPPER> #      - LOGICAL values are not mentioned in CLIPPER doc.s,
    CLIPPER> #        so they may not yet be correct in cfortran.h.
    CLIPPER> #      - K&R mode (-knr or Ac=knr) breaks FLOAT functions
    CLIPPER> #        (see CLIPPER doc.s) and cfortran.h does not fix it up.
    CLIPPER> #        [cfortran.h ok for old sun C which made the same mistake.]
    CLIPPER> acc cfortest.c -c -DCLIPPERFortran
    CLIPPER> af77 cfortex.f cfortest.o -o cfortest

By changing the SELECTion `ifdef` of `cfortest.c` and recompiling one can try out a few dozen different few-line examples.

The benefits of using `cfortran.h` include:

1. Machine/OS/compiler independent mixing of C and FORTRAN.

2. Identical (within syntax) calls across languages, e.g.

       FORTRAN:

             CALL HBOOK1(1,'pT spectrum of pi+',100,0.,5.,0.)

       C:
             HBOOK1(1,"pT spectrum of pi+",100,0.,5.,0.);

3. Each routine need only be set up once in its lifetime. e.g. Setting up a FORTRAN routine to be called by C. ID,...,VMX are merely the names of arguments. These tags must be unique w.r.t. each other but are otherwise arbitrary.

       PROTOCCALLSFSUB6(HBOOK1,hbook1,INT,STRING,INT,FLOAT,FLOAT,FLOAT)
       #define HBOOK1(ID,CHTITLE,NX,XMI,XMA,VMX)                        \
            CCALLSFSUB6(HBOOK1,hbook1,INT,STRING,INT,FLOAT,FLOAT,FLOAT, \
                      ID,CHTITLE,NX,XMI,XMA,VMX)

4. Source code is NOT required for the C routines exported to FORTRAN, nor for the FORTRAN routines imported to C. In fact, routines are most easily prototyped using the information in the routines' documentation.

5. Routines, and the code calling them, can be coded naturally in the language of choice. C routines may be coded with the natural assumption of being called only by C code. `cfortran.h` does all the required work for FORTRAN code to call C routines. Similarly it also does all the work required for C to call FORTRAN routines. Therefore:
   - C programmers need not embed FORTRAN argument passing mechanisms into their code.
   - FORTRAN code need not be converted into C code. i.e. The honed and time-honored FORTRAN routines are called by C.

6. `cfortran.h` is a single ~1700 line C include file; portable to most remaining, if not all, platforms.

7. `STRINGS` and `VECTORS` of `STRINGS` along with the usual simple arguments to routines are supported as are functions returning `STRINGS` or numbers. Arrays of pointers to strings and values of structures as C arguments, will soon be implemented. After learning the machinery of `cfortran.h`, users can expand it to create custom types of arguments. [This requires no modification to `cfortran.h`, all the preprocessor directives required to implement the custom types can be defined outside `cfortran.h`]

8. `cfortran.h` requires each routine to be exported to be explicitly set up. While is usually only be done once in a header file it would be best if applications were required to do no work at all in order to cross languages. `cfortran.h`'s simple syntax could be a convenient back-end for a program which would export FORTRAN or C routines directly from the source code.

### Example 1

`cfortran.h` has been used to make the C header file `hbook.h`, which then gives any C programmer, e.g. `example.c`, full and completely transparent access to CERN's HBOOK library of routines. Each HBOOK routine required about 3 lines of simple code in `hbook.h`. The example also demonstrates how FORTRAN common blocks are defined and used.

    /* hbook.h */
    #include "cfortran.h"
            :
    PROTOCCALLSFSUB6(HBOOK1,hbook1,INT,STRING,INT,FLOAT,FLOAT,FLOAT)
    #define HBOOK1(ID,CHTITLE,NX,XMI,XMA,VMX)                        \
         CCALLSFSUB6(HBOOK1,hbook1,INT,STRING,INT,FLOAT,FLOAT,FLOAT, \
                   ID,CHTITLE,NX,XMI,XMA,VMX)
            :
    /* end hbook.h */

    /* example.c */
    #include "hbook.h"
            :
    typedef struct {
      int lines;
      int status[SIZE];
      float p[SIZE];  /* momentum */
    } FAKE_DEF;
    #define FAKE COMMON_BLOCK(FAKE,fake)
    COMMON_BLOCK_DEF(FAKE_DEF,FAKE);
            :
    main ()
    {
            :
               HBOOK1(1,"pT spectrum of pi+",100,0.,5.,0.);
    /* c.f. the call in FORTRAN:
          CALL HBOOK1(1,'pT spectrum of pi+',100,0.,5.,0.)
    */
            :
      FAKE.p[7]=1.0;
    	:
    }

N.B.

1. The routine is language independent.
2. `hbook.h` is machine independent.
3. Applications using routines via `cfortran.h` are machine independent.

### Example 2

Many VMS System calls are most easily called from FORTRAN, but `cfortran.h` now gives that ease in C.

    #include "cfortran.h"

    PROTOCCALLSFSUB3(LIB$SPAWN,lib$spawn,STRING,STRING,STRING)
    #define LIB$SPAWN(command,input_file,output_file)          \
         CCALLSFSUB3(LIB$SPAWN,lib$spawn,STRING,STRING,STRING, \
                      command,input_file,output_file)

    main ()
    {
    LIB$SPAWN("set term/width=132","","");
    }

Obviously the `cfortran.h` command above could be put into a header file along with the description of the other system calls, but as this example shows, it's not much hassle to set up `cfortran.h` for even a single call.

### Example 3

`cfortran.h` and the source cstring.c create the cstring.obj library which gives FORTRAN access to all the functions in C's system library described by the system's C header file `string.h`.

    C     EXAMPLE.FOR
          PROGRAM EXAMPLE
          DIMENSION I(20), J(30)
            :
          CALL MEMCPY(I,J,7)
            :
          END

    /* cstring.c */
    #include              /* string.h prototypes memcpy() */
    #include "cfortran.h"

            :
    FCALLSCSUB3(memcpy,MEMCPY,memcpy,PVOID,PVOID,INT)
            :

The simplicity exhibited in the above example exists for many but not all machines. Note 4. of Section II ii) details the limitations and describes tools which try to maintain the best possible interface when FORTRAN calls C routines.

## II) Using cfortran.h

The user is asked to look at the source files `cfortest.c` and `cfortex.f` for clarification by example.

### o) Notes:

- Specifying the FORTRAN compiler

  `cfortran.h` generates interfaces for the default i FORTRAN compiler. The default can be overridden by defining with one of the follwoing methods,

  - in the code, e.g.: `#define NAGf90Fortran`

  - in the compile directive, e.g.: `unix> cc -DNAGf90Fortran`
  one of the following before including `cfortran.h`:

       NAGf90Fortran   f2cFortran  hpuxFortran  apolloFortran  sunFortran
        IBMR2Fortran  CRAYFortran  mipsFortran     DECFortran  vmsFortran
       CONVEXFortran       PowerStationFortran          AbsoftUNIXFortran
           SXFortran   pgiFortran                        AbsoftProFortran

  This also allows crosscompilation.

  If wanted, `NAGf90Fortran`, `f2cFortran`, `DECFortran`, `AbsoftUNIXFortran`, `AbsoftProFortran` and `pgiFortran` must be requested by the user.

- `/**/`

  `cfortran.h` (ab)uses the comment kludge `/**/` when the ANSI C preprocessor catenation operator `##` doesn't exist. In at least MIPS C, this kludge is sensitive to blanks surrounding arguments to macros. Therefore, for applications using non-ANSI C compilers, the `argtype_i`, `routine_name`, `routine_type` and `common_block_name arguments` to the `PROTOCCALLSFFUNn`, `CCALLSFSUB/FUNn`, `FCALLSCSUB/FUNn` and `COMMON_BLOCK` macros must not be followed by any white space characters such as blanks, tabs or newlines.

- `LOGICAL`

  FORTRAN `LOGICAL` values of .TRUE. and .FALSE. do not agree with the C representation of TRUE and FALSE on all machines. `cfortran.h` does the conversion for `LOGICAL` and PLOGICAL arguments and for functions returning `LOGICAL`. Users must convert arrays of `LOGICAL`s from C to FORTRAN with the C2FLOGICALV(array_name, elements_in_array); macro. Similarly, arrays of `LOGICAL` values may be converted from the FORTRAN into C representation by using F2CLOGICALV(array_name, elements_in_array);

  When C passes or returns `LOGICAL` values to FORTRAN, by default `cfortran.h` only makes the minimal changes required to the value. [e.g. Set/Unset the single relevant bit or do nothing for FORTRAN compilers which use 0 as FALSE and treat all other values as TRUE.] Therefore `cfortran.h` will pass `LOGICAL`s to FORTRAN which do not have an identical representation to .TRUE. or .FALSE. This is fine except for abuses of FORTRAN/77 in the style of:

             logical l
             if (l .eq. .TRUE.)     ! (1)

  instead of the correct:

             if (l .eqv. .TRUE.)    ! (2)

  or:

             if (l)                 ! (3)

  For FORTRAN code which treats `LOGICAL`s from C in the method of (1), `LOGICAL_STRICT` must be defined before including `cfortran.h`, either in the code, `"#define LOGICAL_STRICT"`, or compile with `"cc -DLOGICAL_STRICT"`. There is no reason to use `LOGICAL_STRICT` for FORTRAN code which does not do (1). At least the IBM's `xlf` and the Apollo's `f77` do not even allow code along the lines of (1).

  DECstations' `DECFortran` and MIPS FORTRAN compilers use different internal representations for `LOGICAL` values. [Both compilers are usually called `f77`, although when both are installed on a single machine the MIPS' one is usually renamed. (e.g. `f77`2.1 for version 2.10.)] `cc` doesn't know which FORTRAN compiler is present, so `cfortran.h` assumes MIPS `f77`. To use `cc` with DECFortran define the preprocessor constant 'DECFortran'. e.g.

                  i)  cc -DDECFortran -c the_code.c

  or

                  ii) #define DECFortran  /* in the C code or add to cfortran.h. */

  MIPS `f77` [SGI and DECstations], `f2c`, and `f77` on VAX Ultrix treat `.eqv./.neqv.` as `.eq./.ne.`. Therefore, for these compilers, `LOGICAL_STRICT` is defined by default in `cfortran.h`. [The Sun and HP compilers have not been tested, so they may also require `LOGICAL_STRICT` as the default.]

- `SHORT` and `BYTE`

  They are irrelevant for the CRAY where FORTRAN has no equivalent to C's `short`. Similarly `BYTE` is irrelevant for `f2c` and for VAX Ultrix `f77` and fort. The author has tested SHORT and BYTE with a modified cfortest.c/cfortex.f on all machines supported except for the HP9000 and the Sun.

  `BYTE` is a signed 8-bit quantity, i.e. values are -128 to 127, on all machines except for the SGI [at least for MIPS Computer Systems 2.0.] On the SGI it is an unsigned 8-bit quantity, i.e. values are 0 to 255, although the SGI 'FORTRAN 77 Programmers Guide' claims BYTE is signed. Perhaps MIPS 2.0 is dated, since the DECstations using MIPS 2.10 `f77` have a signed `BYTE`.

  To minimize the difficulties of signed and unsigned `BYTE`, `cfortran.h` creates the type '`INTEGER_BYTE`' to agree with FORTRAN's `BYTE`. Users may define `SIGNED_BYTE` or `UNSIGNED_BYTE`, before including `cfortran.h`, to specify FORTRAN's `BYTE`. If neither is defined, `cfortran.h` assumes `SIGNED_BYTE`.

- CRAY

  The type `DOUBLE` in `cfortran.h` corresponds to FORTRAN's `DOUBLE PRECISION`. The type `FLOAT` in `cfortran.h` corresponds to FORTRAN's `REAL`.

  On a classic CRAY [i.e. all models except for the t3e]:

      ( 64 bit) C float       == C double == FORTRAN REAL
      (128 bit) C long double             == FORTRAN DOUBLE PRECISION

  Therefore when moving a mixed C and FORTRAN app. to/from a classic CRAY, either the C code will have to change, or the FORTRAN code and `cfortran.h` declarations will have to change. `DOUBLE_PRECISION` is a `cfortran.h` macro which provides the former option, i.e. the C code is automatically changed. `DOUBLE_PRECISION` is 'long double' on classic CRAY and 'double' elsewhere. `DOUBLE_PRECISION` thus corresponds to FORTRAN's `DOUBLE PRECISION` on all machines, including classic CRAY.

  On a classic CRAY with the FORTRAN compiler flag `'-dp'`: FORTRAN `DOUBLE PRECISION` thus is also the faster 64bit type. (This switch is often used since the application is usually satisfied by 64 bit precision and the application needs the speed.) `DOUBLE_PRECISION` is thus not required in this case, since the classic CRAY behaves like all other machines. If `DOUBLE_PRECISION` is used nonetheless, then on the classic CRAY the default `cfortran.h` behavior must be overridden, for example by the C compiler option `'-DDOUBLE_PRECISION=double'`.

  On a CRAY t3e:

      (32 bit) C float                   == FORTRAN Unavailable
      (64 bit) C double == C long double == FORTRAN REAL == FORTRAN DOUBLE PRECISION

  Notes:

  - (32 bit) is available as FORTRAN `REAL*4` and (64 bit) is available as FORTRAN `REAL*8`. Since `cfortran.h` is all about more portability, not about less portability, the use of the nonstandard `REAL*4` and `REAL*8` is strongly discouraged.

  - FORTRAN `DOUBLE PRECISION` is folded to `REAL` with the following warning:

            DOUBLE PRECISION is not supported on this platform.  REAL will be used.

    Similarly, FORTRAN `REAL*16` is mapped to `REAL*8` with a warning. This behavior differs from that of other machines, including the classic CRAY. `FORTRAN_REAL` is thus introduced for the t3e, just as `DOUBLE_PRECISION` is introduced for the classic CRAY. `FORTRAN_REAL` is '`double`' on t3e and '`float`' elsewhere. `FORTRAN_REAL` thus corresponds to FORTRAN's `REAL` on all machines, including t3e.

- `f2c`

  `f2c`, by default promotes `REAL` functions to double. `cfortran.h` does not (yet) support this, so the `f2c -R` option must be used to turn this promotion off.

- `f2c`

  [Thanks to Dario Autiero for pointing out the following.] `f2c` has a strange feature in that either one or two underscores are appended to a FORTRAN name of a routine or common block, depending on whether or not the original name contains an underscore.

         S.I. Feldman et al., "A FORTRAN to C converter",
         Computing Science Technical Report No. 149.

         page 2, chapter 2: INTERLANGUAGE conventions
         ...........

  To avoid conflict with the names of library routines and with names that `f2c` generates, FORTRAN names may have one or two underscores appended. FORTRAN names are forced to lower case (unless the -U option described in Appendix B is in effect); external names, i.e. the names of FORTRAN procedures and common blocks, have a single underscore appended if they do not contain any underscore and have a pair of underscores appended if they do contain underscores. Thus FORTRAN subroutines names `ABC`, `A_B_C` and `A_B_C_` result in C functions named `abc`_, `a_b_c__` and `a_b_c___`.

  `cfortran.h` is unable to change the naming convention on a name by name basis. FORTRAN routine and common block names which do not contain an underscore are unaffected by this feature. Names which do contain an underscore may use the following work-around:

      /* First 2 lines are a completely standard cfortran.h interface
         to the FORTRAN routine E_ASY . */
                        PROTOCCALLSFSUB2(E_ASY,e_asy, PINT, INT)
      #define E_ASY(A,B)     CCALLSFSUB2(E_ASY,e_asy, PINT, INT, A, B)
      #ifdef f2cFortran
      #define e_asy_ e_asy__
      #endif
      /* Last three lines are a work-around for the strange f2c naming feature. */

- NAG f90

  The FORTRAN 77 subset of FORTRAN 90 is supported. Extending `cfortran.h` to interface C with all of FORTRAN 90 has not yet been examined.
  The NAG f90 library hij acks the `main()` of any program and starts the user's program with a call to: `void f90_main(void)`;
  While this in itself is only a minor hassle, a major problem arises because NAG f90 provides no mechanism to access command line arguments.
  At least version 'NAGWare f90 compiler Version 1.1(334)' appended _CB to common block names instead of the usual `_`. To fix, add this to `cfortran.h`:

      #ifdef old_NAG_f90_CB_COMMON
      #define COMMON_BLOCK                 CFC_  /* for all other Fortran compilers */
      #else
      #define COMMON_BLOCK(UN,LN)          _(LN,_CB)
      #endif

- RS/6000

  Using `"xlf -qextname ..."`, which appends an underscore, `'_'`, to all FORTRAN external references, requires `"cc -Dextname ..."` so that `cfortran.h` also generates these underscores. Use i`-Dextname=extname` if `extname` is a symbol used in the C code. The use of `"xlf -qextname"` is strongly encouraged, since it allows for transparent naming schemes when mixing C and FORTRAN.

- HP9000

  Using `"f77 +ppu ..."`, which appends an underscore, `'_'`, to all FORTRAN external references, requires `"cc -Dextname ..."` so that `cfortran.h` also generates these underscores. Use `-Dextname=extname` if extname is a symbol used in the C code. The use of `"f77 +ppu"` is strongly encouraged, since it allows for transparent naming schemes when mixing C and FORTRAN.

  At least one release of the HP `/lib/cpp.ansi` preprocessor is broken and will go into an infinite loop when trying to process `cfortran.h` with the `##` catenation operator. The K&R version of `cfortran.h` must then be used and the K&R preprocessor must be specified. e.g.

      HP9000> cc -Aa -tp,/lib/cpp -c source.c

  The same problem with a similar solution exists on the Apollo. An irrelevant error message `'0: extraneous name /usr/include'` will appear for each source file due to another HP bug, and can be safely ignored. e.g.

      cc -v -c -Aa -tp,/lib/cpp cfortest.c

  will show that the driver passes `'-I /usr/include'` instead of `'-I/usr/include'` to `/lib/cpp`

  On some machines the above error causes compilation to stop; one must then use K&R C, as with old HP compilers which don't support function prototyping. `cfortran.h` has to be informed that K&R C is to being used, e.g.

      HP9000> cc -D__CF__KnR -c source.c

- AbsoftUNIXFortran

  By default, `cfortran.h` follows the default AbsoftUNIX/ProFortran and prepends `_C` to each common block name. To override the `cfortran.h` behavior `#define COMMON_BLOCK(UN,LN)` before including `cfortran.h`. [Search for `COMMON_BLOCK` in `cfortran.h` for examples.]

- Apollo

  On at least one release, 'C compiler 68K Rev6.8(168)', the default C preprocessor, from cc -A xansi or cc -A ansi, enters an infinite loop when using `cfortran.h`. This Apollo bug can be circumvented by using:

  - `cc -DANSI_C_preprocessor=0` to force use of `/**/`, instead of `'##'`.

    AND

  - The pre-ANSI preprocessor, i.e. use `cc -Yp,/usr/lib`

  The same problem with a similar solution exists on the HP.

- Sun

  Old versions of cc(1), say <~1986, may require help for `cfortran.h` applications:

  - `#pragma` may not be understood, hence `cfortran.h` and `cfortest.c` may require

        sun> mv cfortran.h cftmp.h && grep -v "^#pragma" cfortran.h
        sun> mv cfortest.c cftmp.c && grep -v "^#pragma" cfortest.c

  - Old copies of `math.h` may not include the following from a newer `math.h`. [For an ancient `math.h` on a 386 or sparc, get similar from a new `math.h`.]

         #ifdef mc68000     /* 5 lines Copyright (c) 1988 by Sun Microsystems, Inc. */
         #define FLOATFUNCTIONTYPE	int
         #define RETURNFLOAT(x) 		return (*(int *)(&(x)))
         #define ASSIGNFLOAT(x,y)	*(int *)(&x) = y
         #endif

- CRAY, Sun, Apollo [pre 6.8 cc], VAX Ultrix and HP9000

  Only FORTRAN routines with less than 15 arguments can be prototyped for C, since these compilers don't allow more than 31 arguments to a C macro. This can be overcome, [see Section IV], with access to any C compiler without this limitation, e.g. gcc, on ANY machine.

- VAX Ultrix

  `vcc (1)` with `f77` is not supported. Although:

      VAXUltrix> f77 -c cfortex.f
      VAXUltrix> vcc -o cfortest cfortest.c cfortex.o -lI77 -lU77 -lF77  &&  cfortest

  will link and run. However, the FORTRAN standard I/O is NOT merged with the `stdin` and `stdout` of C, and instead uses the files `fort.6` and `fort.5`. For `vcc`, `f77` can't drive the linking, as for `gcc` and `cc`, since `vcc` objects must be linked using `lk (1)`. `f77 -v` doesn't tell much, and without VAX Ultrix manuals, the author can only wait for the info. required.

  `fort (1)` is not supported. Without VAX Ultrix manuals the author cannot convince `vcc/gcc/cc` and `fort` to generate names of routines and common blocks that match at the linker, `lk (1)`. i.e. `vcc/gcc/cc` prepend a single underscore to external references, e.g. `NAME` becomes `_NAME`, while fort does not modify the references. So ... either fort has prepend an underscore to external references, or `vcc/gcc/cc` have to generate unmodified names. `man 1 fort` mentions `JBL`, is JBL the only way?

- VAX VMS C

  The compiler 'easily' exhausts its table space and generates:

      %CC-F-BUGCHECK, Compiler bug check during parser phase    .
                      Submit an SPR with a problem description.
                      At line number 777 in DISK:[DIR]FILE.C;1.

  where the line given, '777', includes a call across C and FORTRAN via `cfortran.h`, usually with >7 arguments and/or very long argument expressions.

  This SPR can be staved off, with the simple modification to `cfortran.h`, such that the relevant `CCALLSFSUBn` (or `CCALLSFFUNn` or `FCALLSCFUNn`) is not cascaded up to `CCALLSFSUB14`, and instead has its own copy of the contents of `CCALLSFSUB14`. [If these instructions are not obvious after examining `cfortran.h` please contact the author.]
  [Thanks go to Mark Kyprianou (kyp@stsci.edu) for this solution.]

- Mips compilers

  e.g. DECstations and SGI, require applications with a C main() and calls to GETARG(3F), i.e. FORTRAN routines returning the command line arguments, to use two macros as shown:

              :
      CF_DECLARE_GETARG;              /* This must be external to all routines.     */
              :
      main(int argc, char *argv[])
      {
              :
      CF_SET_GETARG(argc,argv);       /* This must precede any calls to GETARG(3F). */
              :
      }

  The macros are null and benign on all other systems. Sun's `GETARG(3F)` also doesn't work with a generic C `main()` and perhaps a workaround similar to the Mips' one exists.

- Alpha/OSF

  Using the DEC FORTRAN and the DEC C compilers of DEC OSF/1 [RT] V1.2 (Rev. 10), FORTRAN, when called from C, has occasional trouble using a routine received as a dummy argument. e.g. In the following the FORTRAN routine 'e' will crash when it tries to use the C routine 'c' or the FORTRAN routine 'f'. The example works on other systems.

      C FORTRAN                           /* C */
            integer function f()          #include
            f = 2                         int f_();
            return                        int e_(int (*u)());
            end
                                          int c(){ return 1;}
            integer function e(u)         int d (int (*u)()) { return u();}
            integer u
            external u                    main()
            e=u()                         {         /* Calls to d  work.  */
            return                        printf("d (c ) returns %d.\n",d (c ));
            end                           printf("d (f_) returns %d.\n",d (f_));
                                                    /* Calls to e_ crash. */
                                          printf("e_(c ) returns %d.\n",e_(c ));
                                          printf("e_(f_) returns %d.\n",e_(f_));
                                          }

  Solutions to the problem are welcomed! A kludge which allows the above example to work correctly, requires an extra argument to be given when calling the dummy argument function. i.e. Replacing `'e=u()'` by `'e=u(1)'` allows the above example to work.

- The FORTRAN routines are called using macro expansions, therefore the usual caveats for expressions in arguments apply. The expressions to the routines may be evaluated more than once, leading to lower performance and in the worst case bizarre bugs.

- For those who wish to use `cfortran.h` in large applications. [See Section IV.] This release is intended to make it easy to get applications up and running. This implies that applications are not as efficient as they could be:

  - The current mechanism is inefficient if a single header file is used to describe a large library of FORTRAN functions. Code for a static wrapper fn. is generated in each piece of C source code for each FORTRAN function specified with the `CCALLSFFUNn` statement, irrespective of whether or not the function is ever called.

  - Code for several static utility routines internal to `cfortran.h` is placed into any source code which `#includes cfortran.h`. These routines should probably be in a library.

### i) Calling FORTRAN routines from C:

The FORTRAN routines are defined by one of the following two instructions:

for a SUBROUTINE:

    /* PROTOCCALLSFSUBn is optional for C, but mandatory for C++. */
    PROTOCCALLSFSUBn(ROUTINE_NAME,routine_name,argtype_1,...,argtype_n)
    #define     Routine_name(argname_1,..,argname_n)               \
    CCALLSFSUBn(ROUTINE_NAME,routine_name,argtype_1,...,argtype_n, \
                             argname_1,..,argname_n)

for a FUNCTION:

    PROTOCCALLSFFUNn(routine_type,ROUTINE_NAME,routine_name,argtype_1,...,argtype_n)
    #define     Routine_name(argname_1,..,argname_n)               \
    CCALLSFFUNn(ROUTINE_NAME,routine_name,argtype_1,...,argtype_n, \
                             argname_1,..,argname_n)

Where:

    'n' = 0->14 [SUBROUTINE's ->27] (easily expanded in cfortran.h to > 14 [27]) is
        the number of arguments to the routine.
    Routine_name = C       name of the routine (IN UPPER CASE LETTERS).[see 2.below]
    ROUTINE_NAME = FORTRAN name of the routine (IN UPPER CASE LETTERS).
    routine_name = FORTRAN name of the routine (IN lower case LETTERS).
    routine_type = the type of argument returned by FORTRAN functions.
                 = BYTE, DOUBLE, FLOAT, INT, LOGICAL, LONG, SHORT, STRING, VOID.
                   [Instead of VOID one would usually use CCALLSFSUBn.
                    VOID forces a wrapper function to be used.]
    argtype_i    = the type of argument passed to the FORTRAN routine and must be
                   consistent in the definition and prototyping of the routine s.a.
                 = BYTE, DOUBLE, FLOAT, INT, LOGICAL, LONG, SHORT, STRING.
                 For vectors, i.e. 1 dim. arrays use
                 = BYTEV, DOUBLEV, FLOATV, INTV, LOGICALV, LONGV, SHORTV,
                   STRINGV, ZTRINGV.
                 For vectors of vectors, i.e. 2 dim. arrays use
                 = BYTEVV, DOUBLEVV, FLOATVV, INTVV, LOGICALVV, LONGVV, SHORTVV.
                 For n-dim. arrays, 1<=n<=7 [7 is the maximum in FORTRAN 77],
                 = BYTEV..nV's..V, DOUBLEV..V, FLOATV..V, INTV..V, LOGICALV..V,
                   LONGV..V, SHORTV..V.
                    N.B. Array dimensions and types are checked by the C compiler.
                 For routines changing the values of an argument, the keyword is
                      prepended by a 'P'.
                 = PBYTE, PDOUBLE, PFLOAT, PINT, PLOGICAL, PLONG, PSHORT,
                   PSTRING, PSTRINGV, PZTRINGV.
                 For EXTERNAL procedures passed as arguments use
                 = ROUTINE.
                 For exceptional arguments which require no massaging to fit the
                      argument passing mechanisms use
                 = PVOID.
                    The argument is cast and passed as (void *).
                    Although PVOID could be used to describe all array arguments on
                    most (all?) machines , it shouldn't be because the C compiler
                    can no longer check the type and dimension of the array.
    argname_i    = any valid unique C tag, but must be consistent in the definition
                   as shown.

Notes:

1. `cfortran.h` may be expanded to handle a more argument type. To suppport new arguments requiring complicated massaging when passed between FORTRAN and C, the user will have to understand `cfortran.h` and follow its code and mechanisms.

   To define types requiring little or no massaging when passed between FORTRAN and C, the pseudo argument type `SIMPLE` may be used. For a user defined type called 'newtype', the definitions required are:

       /* The following 7 lines are required verbatim.
          'newtype' is the name of the new user defined argument type.
       */
       #define newtype_cfV(  T,A,B,F)       SIMPLE_cfV(T,A,B,F)
       #define newtype_cfSEP(T,  B)         SIMPLE_cfSEP(T,B)
       #define newtype_cfINT(N,A,B,X,Y,Z)   SIMPLE_cfINT(N,A,B,X,Y,Z)
       #define newtype_cfSTR(N,T,A,B,C,D,E) SIMPLE_cfSTR(N,T,A,B,C,D,E)
       #define newtype_cfCC( T,A,B)         SIMPLE_cfCC(T,A,B)
       #define newtype_cfAA( T,A,B)         newtype_cfB(T,A) /* Argument B not used. */
       #define newtype_cfU(  T,A)           newtype_cfN(T,A)

       /* 'parameter_type(A)' is a declaration for 'A' and describes the type of the
       parameter expected by the FORTRAN function.  This type will be used in the
       prototype for the function, if  using ANSI C, and to declare the argument used
       by the intermediate function if calling a FORTRAN FUNCTION.
       Valid 'parameter_type(A)' include: int A
                                          void (*A)()
                                          double A[17]
       */
       #define newtype_cfN(  T,A)     parameter_type(A)      /* Argument T not used. */

       /* Before any argument of the new type is passed to the FORTRAN routine, it may
       be massaged as given by 'massage(A)'.
       */
       #define newtype_cfB(  T,A)     massage(A)             /* Argument T not used. */

       An example of a simple user defined type is given cfortex.f and cfortest.c.
       Two uses of SIMPLE user defined types are [don't show the 7 verbatim #defines]:

       /* Pass the address of a structure, using a type called PSTRUCT */
       #define PSTRUCT_cfN(  T,A)        void *A
       #define PSTRUCT_cfB(  T,A)       (void *) &(A)

       /* Pass an integer by value, (not standard F77 ), using a type called INTVAL */
       #define INTVAL_cfN(   T,A)      int A
       #define INTVAL_cfB(   T,A)         (A)

       [If using VAX VMS, surrounding the #defines with "#pragma (no)standard" allows
        the %CC-I-PARAMNOTUSED messages to be avoided.]

   Upgrades to `cfortran.h` try to be, and have been, backwards compatible. This compatibility cannot be offered to user defined types. `SIMPLE` user defined types are less of a risk since they require so little effort in their creation. If a user defined type is required in more than one C header file of interfaces to libraries of FORTRAN routines, good programming practice, and ease of code maintenance, suggests keeping any user defined type within a single file which is #included as required. To date, changes to the `SIMPLE` macros were introduced in versions 2.6, 3.0 and 3.2 of `cfortran.h`.

2. `Routine_name` is the name of the macro which the C programmer will use in order to call a FORTRAN routine. In theory `Routine_name` could be any valid and unique name, but in practice, the name of the FORTRAN routine in UPPER CASE works everywhere and would seem to be an obvious choice.

3. `[BYTE|DOUBLE|BYTE|DOUBLE|FLOAT|INT|LOGICAL|LONG|SHORT][V|VV|VVV|...]`

   `cfortran.h` encourages the exact specification of the type and dimension of array parameters because it allows the C compiler to detect errors in the arguments when calling the routine.

   `cfortran.h` does not strictly require the exact specification since the argument is merely the address of the array and is passed on to the calling routine. Any array parameter could be declared as `PVOID`, but this circumvents C's compiletime ability to check the correctness of arguments and is therefore discouraged.

   Passing the address of these arguments implies that `PBYTEV`, `PFLOATV`, ... , `PDOUBLEVV`, ... don't exist in `cfortran.h`, since by default the routine and the calling code share the same array, i.e. the same values at the same memory location.

   These comments do NOT apply to arrays of `(P)S/ZTRINGV`. For these parameters, `cfortran.h` passes a massaged copy of the array to the routine. When the routine returns, `S/ZTRINGV` ignores the copy, while `PS/ZTRINGV` replaces the calling code's original array with copy, which may have been modified by the called routine.

4. `(P)STRING(V)`:

   - `STRING`

     If the argument is a fixed length character array, e.g. char ar[8];, the string is blank, ' ', padded on the right to fill out the array before being passed to the FORTRAN routine. The useful size of the string is the same in both languages, e.g. ar[8] is passed as character*7. If the argument is a pointer, the string cannot be blank padded, so the length is passed as strlen(argument). On return from the FORTRAN routine, pointer arguments are not disturbed, but arrays have the terminating '\0' replaced to its original position. i.e. The padding blanks are never visible to the C code.

   - `PSTRING`

     The argument is massaged as with STRING before being passed to the FORTRAN routine. On return, the argument has all trailing blanks removed, regardless of whether the argument was a pointer or an array.

   - `(P)STRINGV`

     Passes a 1- or 2-dimensional char array. e.g. `char a[7],b[6][8];` `STRINGV` may thus also pass a string constant, e.g. `"hiho"`. `(P)STRINGV` does NOT pass a pointer, e.g. `char *`, to either a 1- or a 2-dimensional array, since it cannot determine the array dimensions. A pointer can only be passed using `(P)ZTRINGV`.

     N.B. If a C routine receives a character array argument, e.g. `char a[2][3]`, such an argument is actually a pointer and my thus not be passed by `(P)STRINGV`. Instead `(P)ZTRINGV` must be used.

   - `STRINGV`

     The elements of the argument are copied into space malloc'd, and each element is padded with blanks. The useful size of each element is the same in both languages. Therefore `char bb[6][8];` is equivalent to `character*7 bb(6)`. On return from the routine the malloc'd space is simply released.

   - `PSTRINGV`

     Since FORTRAN has no trailing `'\0'`, elements in an array of strings are contiguous. Therefore each element of the C array is padded with blanks and strip out C's trailing `'\0'`. After returning from the routine, the trailing `'\0'` is reinserted and kill the trailing blanks in each element.

   Summary: `STRING(V)` arguments are blank padded during the call to the FORTRAN routine, but remain original in the C code. `(P)STRINGV` arguments are blank padded for the FORTRAN call, and after returning from FORTRAN trailing blanks are stripped off.

5. `(P)ZTRINGV`:

   - `(P)ZTRINGV` - is identical to `(P)STRINGV`, except that the dimensions of the array of strings is explicitly specified, which thus also allows a pointer to be passed. `(P)ZTRINGV` can thus pass a 1- or 2-dimensional `char` array, e.g. `char b[6][8]`, or it can pass a pointer to such an array, e.g. `char *p;`. `ZTRINGV` may thus also pass a string constant, e.g. `"hiho"`. If passing a 1-dimensional array, `routine_name_ELEMS_j` (see below) must be 1. [Users of `(P)ZTRINGV` should examine `cfortest.c` for examples.]:

   - `(P)ZTRINGV` must thus be used instead of `(P)STRINGV` whenever `sizeof()` can't be used to determine the dimensions of the array of string or strings. e.g. when calling FORTRAN from C with a `char *` received by C as an argument.

   - There is no `(P)ZTRING` type, since `(P)ZTRINGV` can pass a 1-dimensional array or a pointer to such an array, e.g. `char a[7], *b;` If passing a 1-dimensional array, `routine_name_ELEMS_j` (see below) must be 1.

   - To specify the numbers of elements, `routine_name_ELEMS_j` and `routine_name_ELEMLEN_j` must be defined as shown below before interfacing the routine with `CCALLSFSUBn`, `PROTOCCALLSFFUNn`, etc.

         #define routine_name_ELEMS_j   ZTRINGV_ARGS(k)
                                          [..ARGS for subroutines, ..ARGF for functions.]

     or

         #define routine_name_ELEMS_j   ZTRINGV_NUM(l)

     Where:

                routine_name is as above.
                j            [1-n], is the argument being specifying.
                k            [1-n], the value of the k'th argument is the dynamic number
                             of elements for argument j. The k'th argument must be
                             of type BYTE, DOUBLE, FLOAT, INT, LONG or SHORT.
                l            the number of elements for argument j. This must be an
                             integer constant available at compile time.
                             i.e. it is static.

   - Similarly to specify the useful length, [i.e. don't count C's trailing `'\0'`,] of each element:

         #define routine_name_ELEMLEN_j ZTRINGV_ARGS(m)
                                          [..ARGS for subroutines, ..ARGF for functions.]

     or

         #define routine_name_ELEMLEN_j ZTRINGV_NUM(q)

     Where:

                m            [1-n], as for k but this is the length of each element.
                q            as for l but this is the length of each element.

6. `ROUTINE` The argument is an `EXTERNAL` procedure. When C passes a routine to FORTRAN, the language of the function must be specified as follows: [The case of `some_*_function` must be given as shown.]

   When C passes a C routine to a FORTRAN:

           FORTRAN_ROUTINE(arg1, .... ,
                           C_FUNCTION(SOME_C_FUNCTION,some_c_function),
                           ...., argn);

   and similarly when C passes a FORTRAN routine to FORTRAN:

           FORTRAN_ROUTINE(arg1, .... ,
                           FORTRAN_FUNCTION(SOME_FORT_FUNCTION,some_fort_function),
                           ...., argn);

   If `fcallsc` has been redefined; the same definition of `fcallsc` used when creating the wrapper for '`some_c_function`' must also be defined when `C_FUNCTION` is used. See ii) 5. of this section for when and how to redefine `fcallsc`. `ROUTINE` was introduced with `cfortran.h` version 2.6. Earlier versions of `cfortran.h` used `PVOID` to pass external procedures as arguments. Using `PVOID` for this purpose is no longer recommended since it won't work 'as is' for `apolloFortran`, `hpuxFortran800`, `AbsoftUNIXFortran`, `AbsoftProFortran`.

7. CRAY only:

   In a given piece of source code, where FFUNC is any FORTRAN routine, `FORTRAN_FUNCTION(FFUNC,ffunc)` disallows a previous `#define FFUNC(..) CCALLSFSUBn(FFUNC,ffunc,...)` [ or `CCALLSFFUNn`] in order to make the `UPPER CASE FFUNC` callable from C. `#define Ffunc(..) ...` is OK though, as are obviously any other names.

### ii) Calling C routines from FORTRAN:

Each of the following two statements to export a C routine to FORTRAN create FORTRAN 'wrappers', written in C, which must be compiled and linked along with the original C routines and with the FORTRAN calling code.

FORTRAN callable 'wrappers' may also be created for C macros. i.e. in this section, the term 'C function' may be replaced by 'C macro'.

for C functions returning void:

    FCALLSCSUBn(             Routine_name,ROUTINE_NAME,routine_name,argtype_1,...,argtype_n)

for all other C functions:

    FCALLSCFUNn(routine_type,Routine_name,ROUTINE_NAME,routine_name,argtype_1,...,argtype_n)

Where: 'n' = 0->27 (easily expanded to > 27) stands for the number of arguments to the routine.

    Routine_name = the C       name of the routine. [see 9. below]
    ROUTINE_NAME = the FORTRAN name of the routine (IN UPPER CASE LETTERS).
    routine_name = the FORTRAN name of the routine (IN lower case LETTERS).
    routine_type = the type of argument returned by C functions.
                 = BYTE, DOUBLE, FLOAT, INT, LOGICAL, LONG, SHORT, STRING, VOID.
                   [Instead of VOID, FCALLSCSUBn is recommended.]
    argtype_i    = the type of argument passed to the FORTRAN routine and must be
                   consistent in the definition and prototyping of the routine
                 = BYTE, DOUBLE, FLOAT, INT, LOGICAL, LONG, SHORT, STRING.
                 For vectors, i.e. 1 dim. arrays use
                 = BYTEV, DOUBLEV, FLOATV, INTV, LOGICALV, LONGV, SHORTV, STRINGV.
                 For vectors of vectors, 2 dim. arrays use
                 = BYTEVV, DOUBLEVV, FLOATVV, INTVV, LOGICALVV, LONGVV, SHORTVV.
                 For n-dim. arrays use
                 = BYTEV..nV's..V, DOUBLEV..V, FLOATV..V, INTV..V, LOGICALV..V,
                   LONGV..V, SHORTV..V.
                 For routines changing the values of an argument, the keyword is
                      prepended by a 'P'.
                 = PBYTE, PDOUBLE, PFLOAT, PINT, PLOGICAL, PLONG, PSHORT,
                   PSTRING, PNSTRING, PPSTRING, PSTRINGV.
                 For EXTERNAL procedures passed as arguments use
                 = ROUTINE.
                 For exceptional arguments which require no massaging to fit the
                      argument passing mechanisms use
                 = PVOID.
                    The argument is cast and passed as (void *).

Notes:

1. For FORTRAN calling C++ routines, C++ does NOT easily allow support for: `STRINGV`. `BYTEVV`, `DOUBLEVV`, `FLOATVV`, `INTVV`, `LOGICALVV`, `LONGVV`, `SHORTVV`. `BYTEV..V`, `DOUBLEV..V`, `FLOATV..V`, `INTV..V`, `LOGICALV..V`, `LONGV..V`, `SHORTV..V`. Though there are ways to get around this restriction, the restriction is not serious since these types are unlikely to be used as arguments for a C++ routine.

2. `FCALLSCSUB/FUNn` expect that the routine to be 'wrapped' has been properly prototyped, or at least declared.

3. `cfortran.h` may be expanded to handle a new argument type not already among the above.

4. `[BYTE|DOUBLE|BYTE|DOUBLE|FLOAT|INT|LOGICAL|LONG|SHORT][V|VV|VVV|...]`

   `cfortran.h` encourages the exact specification of the type and dimension of array parameters because it allows the C compiler to detect errors in the arguments when declaring the routine using `FCALLSCSUB/FUNn`, assuming the routine to be 'wrapped' has been properly prototyped.

   `cfortran.h` does not strictly require the exact specification since the argument is merely the address of the array and is passed on to the calling routine. Any array parameter could be declared as `PVOID`, but this circumvents C's compiletime ability to check the correctness of arguments and is therefore discouraged.

   Passing the address of these arguments implies that `PBYTEV`, `PFLOATV`, ... , `PDOUBLEVV`, ... don't exist in `cfortran.h`, since by default the routine and the calling code share the same array, i.e. the same values at the same memory location.

   These comments do NOT apply to arrays of `(P)STRINGV`. For these parameters, `cfortran.h` passes a massaged copy of the array to the routine. When the routine returns, `STRINGV` ignores the copy, while `PSTRINGV` replaces the calling code's original array with copy, which may have been modified by the called routine.

5. `(P(N))STRING` arguments have any trailing blanks removed before being passed to C, the same holds true for each element in `(P)STRINGV`. Space is malloc'd in all cases big enough to hold the original string (elements) as well as C's terminating `'\0'`. i.e. The useful size of the string (elements) is the same in both languages. `P(N)STRING(V)` => the string (elements) will be copied from the malloc'd space back into the FORTRAN bytes. If one of the two escape mechanisms mentioned below for PNSTRING has been used, the copying back to FORTRAN is obviously not relevant.

6. `(PN)STRING`'s, [NOT `PSTRING`'s nor `(P)STRINGV`'s,] behavior may be overridden in two cases. In both cases `PNSTRING` and `STRING` behave identically.

   1. If a `(PN)STRING` argument's first 4 bytes are all the `NUL` character, i.e. `'\0\0\0\0'` the NULL pointer is passed to the C routine.

   2. the `NUL` character, i.e. C strings' terminating `'\0'`, the address of the string is simply passed to the C routine. i.e. The argument is treated in this case as it would be with `PPSTRING`, to which we refer the reader for more detail.

   Mechanism 1. overrides 2. . Therefore, to use this mechanism to pass the `NULL` string, `""`, to C, the first character of the string must obviously be the `NUL` character, but of the first 4 characters in the string, at least one must not be `HEX-00`.

   Example:

       C FORTRAN                                               /* C */
             character*40 str                                  #include "cfortran.h"
       C Set up a NULL as :                                    void cs(char *s) {if (s) printf("%s.\n",s);}
       C    i)  4 NUL characters.                              FCALLSCSUB1(cs,CS,cs,STRING)
       C    ii) NULL pointer.
             character*4 NULL
             NULL = CHAR(0)//CHAR(0)//CHAR(0)//CHAR(0)

             data str/'just some string'/

       C Passing the NULL pointer to cs.
             call cs(NULL)
       C Passing a copy of 'str' to cs.
             call cs(str)
       C Passing address of 'str' to cs. Trailing blanks NOT killed.
             str(40:) = NULL
             call cs(str)
             end

   Strings passed from FORTRAN to C via `(PN)STRING` must not have undefined contents, otherwise undefined behavior will result, since one of the above two escape mechanisms may occur depending on the contents of the string.

   This is not be a problem for `STRING` arguments, which are read-only in the C routine and hence must have a well defined value when being passed in.

   `PNSTRING` arguments require special care. Even if they are write-only in the C routine, `PNSTRING`'s above two escape mechanisms require that the value of the argument be well defined when being passed in from FORTRAN to C. Therefore, unless one or both of `PNSTRING`'s escape mechanisms are required, `PSTRING` should be used instead of `PNSTRING`. Prior to version 2.8, `PSTRING` did have the above two escape mechanisms, but they were removed from `PSTRING` to allow strings with undefined contents to be passed in. `PNSTRING` behaves like the old `PSTRING`. [Thanks go to Paul Dubois (`dubios@icf.llnl.gov`) for pointing out that `PSTRING` must allow for strings with undefined contents to be passed in.]

   Example:

       C FORTRAN                                               /* C */
             character*10 s,sn                                 #include "cfortran.h"
                                                               void ps(char *s) {strcpy(s,"hello");}
       C Can   call ps  with undef. s.                         FCALLSCSUB1(ps,PS,ps,PSTRING)
             call ps(s)                                        FCALLSCSUB1(ps,PNS,pns,PNSTRING)
             print *,s,'=s'

       C Can't call pns with undef. s.
       C e.g. If first 4 bytes of s were
       C      "\0\0\0\0", ps would try
       C      to copy to NULL because
       C      of PNSTRING mechanism.
             sn = ""
             call pns(sn)
             print *,sn,'=sn'

             end

7. `PPSTRING` The address of the string argument is simply passed to the C routine. Therefore the C routine and the FORTRAN calling code share the same string at the same memory location. If the C routine modifies the string, the string will also be modified for the FORTRAN calling code. The user is responsible for negociating the differences in representation of a string in FORTRAN and in C, i.e. the differences are not automatically resolved as they are for `(P(N)STRING(V)`. This mechanism is provided for two reasons:

   - Some C routines require the string to exist at the given memory location, after the C routine has exited. Recall that for the usual `P(N)STRING(V)` mechanism, a copy of the FORTRAN string is given to the C routine, and this copy ceases to exist after returning to the FORTRAN calling code.

   - This mechanism can save runtime CPU cycles over (`P(N)STRING(V)`, since it does not perform their malloc, copy and kill trailing blanks of the string to be passed.
     Only in a small minority of cases does the potential benefit of the saved CPU cycles outweigh the programming effort required to manually resolve the differences in representation of a string in FORTRAN and in C.

   For arguments passed via `PPSTRING`, the argument passed may also be an array of strings.

8. `ROUTINE` ANSI C requires that the type of the value returned by the routine be known, For all ROUTINE arguments passed from FORTRAN to C, the type of `ROUTINE` is specified by defining a cast as follows:

       #undef  ROUTINE_j
       #define ROUTINE_j   (cast)

   Where:

              j            [1-n], is the argument being specifying.
              (cast)       is a cast matching that of the argument expected by the C
                           function protoytpe for which a wrapper is being defined.

   e.g. To create a FORTRAN wrapper for `qsort(3C)`:

       #undef  ROUTINE_4
       #define ROUTINE_4 (int (*)(void *,void *))
       FCALLSCSUB4(qsort,FQSORT,fqsort,PVOID,INT,INT,ROUTINE)

   In order to maintain backward compatibility, `cfortran.h` defines a generic cast for `ROUTINE_1`, `ROUTINE_2`, ..., `ROUTINE_27`. The user's definition is therefore strictly required only for DEC C, which at the moment is the only compiler which insists on the correct cast for pointers to functions.

   When using the `ROUTINE` argument inside some FORTRAN code:

   - it is difficult to pass a C routine as the parameter, since in many FORTRAN implementations, FORTRAN has no access to the normal C namespace. e.g. For most UNIX, FORTRAN implicitly only has access to C routines ending in `_`. If the calling FORTRAN code receives the routine as a parameter it can of course easily pass it along.

   - if a FORTRAN routine is passed directly as the parameter, the called C routine must call the parameter routine using the FORTRAN argument passing conventions.

   - if a FORTRAN routine is to be passed as the parameter, but if FORTRAN can be made to pass a C routine as the parameter, then it may be best to pass a C-callable wrapper for the FORTRAN routine. The called C routine is thus spared all FORTRAN argument passing conventions. `cfortran.h` can be used to create such a C-callable wrapper to the parameter FORTRAN routine.

   ONLY PowerStationFortran:

   This FORTRAN provides no easy way to pass a FORTRAN routine as an argument to a C routine. The problem arises because in FORTRAN the stack is cleared by the called routine, while in C/C++ it is cleared by the caller. The C/C++ stack clearing behavior can be changed to that of FORTRAN by using `stdcall__` in the function prototype. The `stdcall__` cannot be applied in this case since the called C routine expects the ROUTINE parameter to be a C routine and does not know that it should apply `stdcall__`. In principle the `cfortran.h` generated FORTRAN callable wrapper for the called C routine should be able to massage the `ROUTINE` argument such that `stdcall__` is performed, but it is not yet known how this could be easily done.

9. The following instructions are not required for VAX/VMS:

   `(P)STRINGV` information [NOT required for VAX VMS]: `cfortran.h` cannot convert the FORTRAN vector of `STRINGS` to the required C vector of `STRINGS` without explicitly knowing the number of elements in the vector. The application must do one of the following for each `(P)STRINGV` argument in a routine before that routine's `FCALLSCFUNn/SUBn` is called:

       #define routine_name_STRV_Ai NUM_ELEMS(j)
        or
       #define routine_name_STRV_Ai NUM_ELEM_ARG(k)
        or
       #define routine_name_STRV_Ai TERM_CHARS(l,m)

   where:

              routine_name     is as above.
              i [i=1->n.]      specifies the argument number of a STRING VECTOR.
              j                would specify a fixed number of elements.
              k [k=1->n. k!=i] would specify an integer argument which specifies the
                               number of elements.
              l [char]         the terminating character at the beginning of an
                               element, indicating to cfortran.h that the preceding
                               elements in the vector are the valid ones.
              m [m=1-...]      the number of terminating characters required to appear
                               at the beginning of the terminating string element.
                               The terminating element is NOT passed on to
                               the C routine.

       e.g.      #define ce_STRV_A1 TERM_CHARS(' ',2)
                 FCALLSCSUB1(ce,CE,ce,STRINGV)

   `cfortran.h` will pass on all elements, in the 1st and only argument to the C routine ce, of the `STRING VECTOR` until, but not including, the first string element beginning with 2 blank, `' '`, characters.

10. Instructions required only for FORTRAN compilers which generate routine names which are undistinguishable from c routine names:
    i.e.

                VAX VMS
                AbsoftUNIXFortran (AbsoftProFortran ok, since it uses Uppercase names.)
                HP9000      if not using the +ppu      option of f77
                IBM RS/6000 if not using the -qextname option of xlf

    Call them the `same_namespace` compilers.

    `FCALLSCSUBn(...)` and `FCALLSCFUNn(...)`, when compiled, are expanded into 'wrapper' functions, so called because they wrap around the original C functions and interface the format of the original C functions' arguments and return values with the format of the FORTRAN call.

    Ideally one wants to be able to call the C routine from FORTRAN using the same name as the original C name. This is not a problem for FORTRAN compilers which append an underscore, `'_'`, to the names of routines, since the original C routine has the name 'name', and the FORTRAN wrapper is called `'name_'`. Similarly, if the FORTRAN compiler generates upper case names for routines, the original C routine `'name'` can have a wrapper called `'NAME'`, [Assuming the C routine name is not in upper case.] For these compilers, e.g. Mips, CRAY, IBM RS/6000 `'xlf -qextname'`, HP-UX 'f77 +ppu', the naming of the wrappers is done automatically.

    For `same_namespace` compilers things are not as simple, but `cfortran.h` tries to provide tools and guidelines to minimize the costs involved in meeting their constraints. The following two options can provide `same_namespace` compilers with distinct names for the wrapper and the original C function.

    These compilers are flagged by `cfortran.h` with the `CF_SAME_NAMESPACE` constant, so that the change in the C name occurs only when required.

    For the remainder of the discussion, routine names generated by FORTRAN compilers are referred to in lower case, these names should be read as upper case for the appropriate compilers.

    HP9000 (When `f77 +ppu` is not used.)

    `f77` has a `-U` option which forces uppercase external names to be generated. Unfortunately, `cc` does not handle recursive macros. Hence, if one wished to use `-U` for separate C and FORTRAN namespaces, one would have to adopt a different convention of naming the macros which allow C to call FORTRAN subroutines. (Functions are not a problem.) The macros are currently the uppercase of the original FORTRAN name, and would have to be changed to lower case or mixed case, or to a different name. (Lower case would of course cause conflicts on many other machines.) Therefore, it is suggested that `f77 -U` not be used, and instead that Option a) or Option b) outlined below be used.

    VAX/VMS:

    For the name used by FORTRAN in calling a C routine to be the same as that of the C routine, the source code of the C routine is required. A preprocessor directive can then force the C compiler to generate a different name for the C routine. e.g.

                            #if defined(vms)
                            #define name name_
                            #endif
                            void name() {printf("name: was called.\n");}
                            FCALLSCSUB0(name,NAME,name)

    In the above, the C compiler generates the original routine with the name `'name_'` and a wrapper called `'NAME'`. This assumes that the name of the routine, as seen by the C programmer, is not in upper case. The VAX VMS linker is not case sensitive, allowing `cfortran.h` to export the upper case name as the wrapper, which then doesn't conflict with the routine name in C. Since the IBM, HP and AbsoftUNIXFortran platforms have case sensitive linkers this technique is not available to them.

    The above technique is required even if the C name is in mixed case, see Option a) for the other compilers, but is obviously not required when Option b) is used.

    Option a) Mixed Case names for the C routines to be called by FORTRAN.

    If the original C routines have mixed case names, there are no name space conflicts.

    Nevertheless for VAX/VMS, the technique outlined above must also be used.

    Option b) Modifying the names of C routines when used by FORTRAN: The more robust naming mechanism, which guarantees portability to all machines, 'renames' C routines when called by FORTRAN. Indeed, one must change the names on `same_namespace` compilers when FORTRAN calls C routines for which the source is unavailable. [Even when the source is available, renaming may be preferable to Option a) for large libraries of C routines.]

    Obviously, if done for a single type of machine, it must be done for all machines since the names of routines used in FORTRAN code cannot be easily redefined for different machines.

    The simplest way to achieve this end is to do explicitly give the modified FORTRAN name in the `FCALLSCSUBn(...)` and `FCALLSCFUNn(...)` declarations. e.g.

        FCALLSCSUB0(name,CFNAME,cfname)

    This allows FORTRAN to call the C routine `'name'` as `'cfname'`. Any name can of course be used for a given routine when it is called from FORTRAN, although this is discouraged due to the confusion it is sure to cause. e.g. Bizarre, but valid and allowing C's `'call_back'` routine to be called from FORTRAN as `'abcd'`:

        FCALLSCSUB0(call_back,ABCD,abcd)

    `cfortran.h` also provides preprocessor directives for a systematic 'renaming' of the C routines when they are called from FORTRAN. This is done by redefining the fcallsc macro before the `FCALLSCSUB/FUN/n` declarations as follows:

        #undef  fcallsc
        #define fcallsc(UN,LN) preface_fcallsc(CF,cf,UN,LN)

        FCALLSCSUB0(hello,HELLO,hello)

    Will cause C's routine 'hello' to be known in FORTRAN as `'cfhello'`. Similarly all subsequent `FCALLSCSUB/FUN/n` declarations will generate wrappers to allow FORTRAN to call C with the C routine's name prefaced by `'cf'`. The following has the same effect, with subsequent `FCALLSCSUB/FUN/n`'s appending the modifier to the original C routines name.

        #undef  fcallsc
        #define fcallsc(UN,LN) append_fcallsc(Y,y,UN,LN)

        FCALLSCSUB0(Xroutine,ROUTINE,routine)

    Hence, C's Xroutine is called from FORTRAN as:

               CALL XROUTINEY()

    The original behavior of `FCALLSCSUB/FUN/n`, where FORTRAN routine names are left identical to those of C, is returned using:

        #undef  fcallsc
        #define fcallsc(UN,LN) orig_fcallsc(UN,LN)

    In C, when passing a C routine, i.e. its wrapper, as an argument to a FORTRAN routine, the FORTRAN name declared is used and the correct fcallsc must be in effect. E.g. Passing 'name' and 'routine' of the above examples to the FORTRAN routines, `FT1` and `FT2`, respectively:

        /* This might not be needed if fcallsc is already orig_fcallsc. */
        #undef  fcallsc
        #define fcallsc(UN,LN) orig_fcallsc(UN,LN)
        FT1(C_FUNCTION(CFNAME,cfname));

        #undef  fcallsc
        #define fcallsc(UN,LN) append_fcallsc(Y,y,UN,LN)
        FT1(C_FUNCTION(XROUTINE,xroutine));

    If the names of C routines are modified when used by FORTRAN, fcallsc would usually be defined once in a header_file.h for the application. This definition would then be used and be valid for the entire application and fcallsc would at no point need to be redefined.

    Once again: the definitions, instructions, declarations and difficulties described here, note 9. OF II ii), apply only for,

                       VAX VMS
                       IBM RS/6000 WITHOUT THE -qextname OPTION FOR xlf, OR
                       HP-UX       WITHOUT THE +ppu      OPTION FOR f77
                       AbsoftUNIXFortran

    and apply only when creating wrappers which enable FORTRAN to call c routines.

### iii) Using C to manipulate FORTRAN COMMON BLOCKS:

FORTRAN common blocks are set up with the following three constructs:

1.     #define Common_block_name COMMON_BLOCK(COMMON_BLOCK_NAME,common_block_name)

       Common_block_name is in UPPER CASE.
       COMMON_BLOCK_NAME is in UPPER CASE.
       common_block_name is in lower case.

   [`Common_block_name` actually follows the same 'rules' as `Routine_name` in Note 2. of II i).] This construct exists to ensure that C code accessing the common block is machine independent.

2.     COMMON_BLOCK_DEF(TYPEDEF_OF_STRUCT, Common_block_name);

   where

       typedef { ... } TYPEDEF_OF_STRUCT;

   declares the structure which maps on to the common block. The `#define` of `Common_block_name` must come before the use of `COMMON_BLOCK_DEF`.

3. In exactly one of the C source files, storage should be set aside for the common block with the definition:

       TYPEDEF_OF_STRUCT  Common_block_name;

   The above definition may have to be omitted on some machines for a common block which is initialized by FORTRAN `BLOCK DATA` or is declared with a smaller size in the C routines than in the FORTRAN routines.

   The rules for common blocks are not well defined when linking/loading a mixture of C and FORTRAN, but the following information may help resolve problems.

   From the 2nd or ANSI ed. of K&R C, p.31, last paragraph:

   i) An external variable must be defined, exactly once, outside of any function; this sets aside storage for it.

   ii) The variable must also be declared in each function that wants to access it; ... The declaration ... may be implicit from context.

   In FORTRAN, every routine says `'common /bar/ foo'`, i.e. part ii) of the above, but there's no part i) requirement. `cc/ld` on some machines don't require i) either. Therefore, when handling FORTRAN, and sometimes C, the loader/linker must automagically set aside storage for common blocks.

   Some loaders, including at least one for the CRAY, turn off the 'automagically set aside storage' capability for FORTRAN common blocks, if any C object declares that common block. Therefore, C code should define, i.e. set aside storage, for the the common block as shown above. e.g.

       C Fortran
             common /fcb/  v,w,x
             character *(13) v, w(4), x(3,2)

       /* C */
       typedef struct { char v[13],w[4][13],x[2][3][13]; } FCB_DEF;
       #define Fcb COMMON_BLOCK(FCB,fcb)
       COMMON_BLOCK_DEF(FCB_DEF,Fcb);
       FCB_DEF Fcb;      /* Definition, which sets aside storage for Fcb, */
                         /* may appear in at most one C source file.      */

   C programs can place a string (or a multidimensional array of strings) into a FORTRAN common block using the following call:

       C2FCBSTR( CSTR, FSTR,DIMENSIONS);

   where:
   `CSTR` is a pointer to the first element of C's copy of the string (array). The C code must use a duplicate of, not the original, common block string, because the FORTRAN common block does not allocate space for C strings' terminating '\0'.
   `FSTR` is a pointer to the first element of the string (array) in the common block.
   `DIMENSIONS` is the number of dimensions of string array. e.g.

                 char a[10]      has DIMENSIONS=0.
                 char aa[10][17] has DIMENSIONS=1.
                 etc...

   `C2FCBSTR` will copy the string (array) from `CSTR` to `FSTR`, padding with blanks, ' ', the trailing characters as required. `C2FCBSTR` uses `DIMENSIONS` and `FSTR` to determine the lengths of the individual string elements and the total number of elements in the string array.

   Note that:

   - the number of string elements in `CSTR` and `FSTR` are identical.
   - for arrays of strings, the useful lengths of strings in `CSTR` and `FSTR` must be the same. i.e. `CSTR` elements each have 1 extra character to accommodate the terminating `'\0'`.
   - On most non-ANSI compilers, the `DIMENSION` argument cannot be prepended by any blanks.

   `FCB2CSTR( FSTR, CSTR,DIMENSIONS)` is the inverse of `C2FCBSTR`, and shares the same arguments and caveats. `FCB2CSTR` copies each string element of `FSTR` to `CSTR`, minus FORTRAN strings' trailing blanks.

   `cfortran.h` users are strongly urged to examine the common block examples in `cfortest.c` and `cfortex.f`. The use of strings in common blocks is demonstrated, along with a suggested way for C to imitate FORTRAN `EQUIVALENCE`'d variables.

**** USERS OF CFORTRAN.H NEED READ NO FURTHER ****

## III) Some Musings

`cfortran.h` is simple enough to be used by the most basic of applications, i.e. making a single C/FORTRAN routine available to the FORTRAN/C programmers. Yet `cfortran.h` is powerful enough to easily make entire C/FORTRAN libraries available to FORTRAN/C programmers.

`cfortran.h` is the ideal tool for FORTRAN libraries which are being (re)written in C, but are to (continue to) support FORTRAN users. It allows the routines to be written in 'natural C', without having to consider the FORTRAN argument passing mechanisms of any machine. It also allows C code accessing these rewritten routines, to use the C entry point. Without `cfortran.h`, one risks the perverse practice of C code calling a C function using FORTRAN argument passing mechanisms!

Perhaps the philosophy and mechanisms of `cfortran.h` could be used and extended to create other language bridges such as ADAFORTRAN, CPASCAL, COCCAM, etc.

The code generation machinery inside `cfortran.h`, i.e. the global structure is quite good, being clean and workable as seen by its ability to meet the needs and constraints of many different compilers. Though the individual instructions of the A..., C..., T..., R... and K... tables deserve to be cleaned up.

## IV) Getting Serious with cfortran.h

`cfortran.h` is set up to be as simple as possible for the casual user. While this ease of use will always be present, 'hooks', i.e. preprocessor directives, are required in `cfortran.h` so that some of the following 'inefficiencies' can be eliminated if they cause difficulties:

- `cfortran.h` contains a few small routines for string manipulation. These routines are declared static and are included and compiled in all source code which uses `cfortran.h`. Hooks should be provided in `cfortran.h` to create an object file of these routines, allowing `cfortran.h` to merely prototypes these routines in the application source code. This is the only 'problem' which afflicts both halves of `cfortran.h`. The remaining discussion refers to the C calls FORTRAN half only.

- Similar to the above routines, `cfortran.h` generates code for a 'wrapper' routine for each FUNCTION exported from FORTRAN. Again `cfortran.h` needs preprocessor directives to create a single object file of these routines, and to merely prototype them in the applications.

- Libraries often contain hundreds of routines. While the preprocessor makes quick work of generating the required interface code from `cfortran.h` and the application.h's, it may be convenient for very large stable libraries to have final_application.h's which already contain the interface code, i.e. these final_application.h's would not require `cfortran.h`. [The convenience can be imagined for the VAX VMS CC compiler which has a fixed amount of memory for preprocessor directives. Not requiring `cfortran.h`, with its hundreds of directives, could help prevent this compiler from choking on its internal limits quite so often.]

With a similar goal in mind, `cfortran.h` defines 100's of preprocessor directives. There is always the potential that these will clash with other tags in the users code, so final_applications.h, which don't require `cfortran.h`, also provide the solution.

In the same vein, routines with more than 14 arguments can not be interfaced by `cfortran.h` with compilers which limit C macros to 31 arguments. To resolve this difficulty, final_application.h's can be created on a compiler without this limitation.

Therefore, new machinery is required to do:

    application.h + cfortran.h => final_application.h

The following example may help clarify the means and ends:

If the following definition of the `HBOOK1` routine, the `/*commented_out_part*/`, is passed through the preprocessor [perhaps #undefing and #defining preprocessor constants if creating an `application.h` for compiler other than that of the preprocessor being used, e.g. `cpp -Umips -DCRAY ...` ] :

    #include "cfortran.h"
    PROTOCCALLSFSUB6(HBOOK1,hbook1,INT,STRING,INT,FLOAT,FLOAT,FLOAT)
    /*#define HBOOK1(ID,CHTITLE,NX,XMI,XMA,VMX)                 \*/
         CCALLSFSUB6(HBOOK1,hbook1,INT,STRING,INT,FLOAT,FLOAT,FLOAT, \
                     ID,CHTITLE,NX,XMI,XMA,VMX)

A function prototype is produced by the `PROTOCCALLSFSUB6(...)`. Interface code is produced, based on the 'variables', `ID,CHTITLE,NX,XMI,XMA,VMX` which will correctly massage a `HBOOK1` call. Therefore, adding the #define line:

    'prototype code'
    #define HBOOK1(ID,CHTITLE,NX,XMI,XMA,VMX)                 \
     'interface code'(ID,CHTITLE,NX,XMI,XMA,VMX)

which is placed into `final_application.h`.

The only known limitation of the above method does not allow the 'variable' names to include `B1,B2,...,B9,BA,BB,...` Obviously the machinery to automatically generate `final_applications.h` from `cfortran.h` and `applications.h` needs more than just some preprocessor directives, but a fairly simple unix shell script should be sufficient. Any takers?

## V) Machine Dependencies of cfortran.h

Porting `cfortran.h` applications, e.g. the `hbook.h` and `cstring.c` mentioned above, to other machines is trivial since they are machine independent. Porting `cfortran.h` requires a solid knowledge of the new machines C preprocessor, and its FORTRAN argument passing mechanisms. Logically `cfortran.h` exists as two halves, a "C CALLS FORTRAN" and a "FORTRAN CALLS C" utility. In some cases it may be perfectly reasonable to port only 'one half' of `cfortran.h` onto a new system.

The lucky programmer porting `cfortran.h` to a new machine, must discover the FORTRAN argument passing mechanisms. A safe starting point is to assume that variables and arrays are simply passed by reference, but nothing is guaranteed. Strings, and n-dimensional arrays of strings are a different story. It is doubtful that any systems do it quite like VAX VMS does it, so that a UNIX or `f2c` versions may provide an easier starting point.

`cfortran.h` uses and abuses the preprocessor's `##` operator. Although the `##` operator does not exist in many compilers, many kludges do. `cfortran.h` uses `/**/` with no space allowed between the slashes, `'/'` , and the macros or tags to be concatenated. e.g.

    #define concat(a,b) a/**/b   /* works*/
    main()
    {
      concat(pri,ntf)("hello");           /* e.g. */
    }

N.B. On some compilers without ##, /**/ may also not work. The author may be able to offer alternate kludges.

## VI) Bugs in vendors C compilers and other curiosities

1. ULTRIX xxxxxx 4.3 1 RISC
   Condolences to long suffering ultrix users! DEC supplies a working C front end for alpha/OSF, but not for ultrix.

   From K&R ANSI C p. 231:

          ultrix> cat cat.c
          #define cat(x, y) x ## y
          #define xcat(x,y) cat(x,y)
          cat(cat(1,2),3)
          xcat(xcat(1,2),3)
          ultrix> cc -E cat.c
          123                  <---- Should be: cat(1,2)3
          123                  <---- Correct.
          ultrix>

   The problem for `cfortran.h`, preventing use of -std and -std1:

          ultrix> cat c.c
          #define cat(x, y) x ## y
          #define xcat(x,y) cat(x,y)
          #define AB(X) X+X
          #define C(E,F,G)  cat(E,F)(G)
          #define X(E,F,G) xcat(E,F)(G)
          C(A,B,2)
          X(A,B,2)
          ultrix> cc -std1 -E c.c
          2+2
          AB  (2)              <---- ?????????????
          ultrix>
          ultrix> cc -std0 -E c.c
          2+2
          AB(2)                <---- ?????????????
          ultrix>

   Due to further ultrix preprocessor problems, for all definitions of definitions with arguments, `cfortran.h` >= 3.0 includes the arguments and recommends the same, even though it is not required by ANSI C. e.g. Users are advised to do

          #define fcallsc(UN,LN) orig_fcallsc(UN,LN)

   instead of

          #define fcallsc        orig_fcallsc

   since ultrix fails to properly preprocess the latter example. CRAY used to (still does?) occasionally trip up on this problem.

2. ConvexOS convex C210 11.0 convex

   In a program with a C main, output to `LUN=6=*` from FORTRAN goes into `$pwd/fort.6` instead of stdout. Presumably, a magic incantation can be called from the C main in order to properly initialize the FORTRAN I/O.

3. SunOS 5.3 Generic_101318-69 sun4m sparc

   The default data and code alignments produced by cc, gcc and `f77` are compatible. If deviating from the defaults, consistent alignment options must be used across all objects compiled by cc and `f77`. [Does gcc provide such options?]

4. `SunOS 5.3 Generic_101318-69 sun4m sparc` with `cc: SC3.0.1 13 Jul 1994` or equivalently `ULTRIX 4.4 0 RISC` using `cc -oldc` are K&R C preprocessors that suffer from infinite loop macros, e.g.

         zedy03> cat src.c
         #include "cfortran.h"
                                   PROTOCCALLSFFUN1(INT,FREV,frev, INTV)
         #define FREV(A1)               CCALLSFFUN1(    FREV,frev, INTV, A1)
         /* To avoid the problem, deletete these ---^^^^--- spaces.    */
         main() { static int a[] = {1,2}; FREV(a); return EXIT_SUCCESS; }

         zedy03> cc -c -Xs -v -DMAX_PREPRO_ARGS=31 -D__CF__KnR src.c
         "src.c", line 4: FREV: actuals too long
         "src.c", line 4: FREV: actuals too long
         .... 3427 more lines of the same message
         "src.c", line 4: FREV: actuals too long
         cc : Fatal error in /usr/ccs/lib/cpp
         Segmentation fault (core dumped)

5. Older sun C compilers

   To link to `f77` objects, older sun C compilers require the `math.h` macros:

       #define RETURNFLOAT(x)   { union {double _d; float _f; } _kluge; \
                                  _kluge._f = (x); return _kluge._d;   }
       #define ASSIGNFLOAT(x,y) { union {double _d; float _f; } _kluge; \
                                  _kluge._d = (y); x = _kluge._f;      }

   Unfortunately, in at least some copies of the sun `math.h`, the semi-colon for `'float _f;'` is left out, leading to compiler warnings.

   The solution is to correct `math.h`, or to change `cfortran.h` to `#define` `RETURNFLOAT(x)` and `ASSIGNFLOAT(x,y)` instead of including `math.h`.

6. gcc version 2.6.3 and probably all other versions as well:

   Unlike all other C compilers supported by `cfortran.h`, `'gcc -traditional'` promotes to double all functions returning float as demonstrated bu the following example.

       /* m.c */
       #include
       int main() { FLOAT_FUNCTION d(); float f; f = d(); printf("%f\n",f); return 0; }

       /* d.c */
       float d() { return -123.124; }

       burow[29] gcc -c -traditional d.c
       burow[30] gcc -DFLOAT_FUNCTION=float m.c d.o && a.out
       0.000000
       burow[31] gcc -DFLOAT_FUNCTION=double m.c d.o && a.out
       -123.124001
       burow[32]

   Thus, `'gcc -traditional'` is not supported by `cfortran.h`. Support would require the same `RETURNFLOAT`, etc. macro machinery present in old sun `math.h`, before sun gave up the same promotion.

7. CRAY

   At least some versions of the t3e and t3d C preprocessor are broken in the fashion described below. At least some versions of the t90 C preprocessor do not have this problem.

   On the CRAY, all FORTRAN names are converted to uppercase. Generally the uppercase name is also used for the macro interface created by `cfortran.h`.

   For example, in the following interface, EASY is both the name of the macro in the original C code and EASY is the name of the resulting function to be called.

       #define EASY(A,B)      CCALLSFSUB2(EASY,easy, PINT, INTV, A, B)

   The fact that a macro called `EASY()` expands to a function called `EASY()` is not a problem for a working C preprocessor. From Kernighan and Ritchie, 2nd edition, p.230:

   In both kinds of macro, the replacement token sequence is repeatedly rescanned for more identifiers. However, once a given identifier has been replaced in a given expansion, it is not replaced if it turns up again during rescanning; instead it is left unchanged.

   Unfortunately, some CRAY preprocessors are broken and don't obey the above rule. A work-around is for the user to NOT use the uppercase name of the name of the macro interface provided by `cfortran.h`. For example:

       #define Easy(A,B)      CCALLSFSUB2(EASY,easy, PINT, INTV, A, B)

   Luckily, the above work-around is not required since the following work-around within `cfortran.h` also circumvents the bug:

          /* (UN), not UN, is required in order to get around  CRAY preprocessor bug.*/
          #define CFC_(UN,LN)            (UN)      /* Uppercase FORTRAN symbols.     */

   Aside: The Visual C++ compiler is happy with UN, but barfs on (UN), so either (UN) causes nonstandard C/C++ or Visual C++ is broken.

## VII) History and Acknowledgements

1.0 | Supports VAX VMS using C 3.1 and FORTRAN 5.4. | Oct. '90.
1.0 | Supports Silicon Graphics w. Mips Computer 2.0 `f77` and cc. [Port of C calls FORTRAN half only.] | Feb. '91.
1.1 | Supports Mips Computer System 2.0 `f77` and cc. [Runs on at least: Silicon Graphics IRIX 3.3.1 DECstations with Ultrix V4.1] | Mar. '91.
1.2 | Internals made simpler, smaller, faster, stronger. Mips version works on IBM RS/6000, this is now called the unix version. | May '91.
1.3 | UNIX and VAX VMS versions are merged into a single `cfortran.h`. C can help manipulate (arrays of) strings in FORTRAN common blocks. Dimensions of string arrays arguments can be explicit. Supports Apollo DomainOS 10.2 (sys5.3) with `f77` 10.7 and cc 6.7. | July '91.
2.0 | Improved code generation machinery creates K&R or ANSI C. Supports Sun, CRAY. `f2c` with vcc on VAX Ultrix. `cfortran.h` macros now require routine and COMMON block names in both upper and lower case. No changes required to applications though. PROTOCCALLSFSUBn is eliminated, with no loss to `cfortran.h` performance. Improved tools and guidelines for naming C routines called by FORTRAN. | Aug. '91.
2.1 | `LOGICAL` correctly supported across all machines. Improved support for `DOUBLE PRECISION` on the CRAY. HP9000 fully supported. VAX Ultrix cc or gcc with `f77` now supported. | Oct. '91.
2.2 | SHORT, i.e. INTEGER*2, and BYTE now supported. `LOGICAL_STRICT` introduced. More compact and robust internal tables. typeV and typeVV for type = BYTE, DOUBLE, FLOAT, INT, `LOGICAL`, LONG,SHORT. FORTRAN passing strings and NULL pointer to C routines improved. | Dec. '91.
2.3 | Extraneous arguments removed from many internal tables. Introduce pseudo argument type SIMPLE for user defined types. LynxOS using `f2c` supported. (Tested with LynxOS 2.0 386/AT.) | May '92.
2.4 | Separation of internal C and FORTRAN compilation directives. `f2c` and NAG f90 supported on all machines. | Oct. '92.
2.5 | Minor mod.s to source and/or doc for HP9000, `f2c`, and NAG f90. | Nov. '92.
2.6 | Support external procedures as arguments with type ROUTINE. | Dec. '92.
2.7 | Support Alpha VMS. Support HP9000 f77 +ppu Support arrays with up to 7 dimensions. Minor mod. of FORTRAN NULL to C via (P)STRING. Specify the type of ROUTINE passed from FORTRAN to C [ANSI C requirement.] Macros never receive a null parameter [RS/6000 requirement.] | Jan. '93.
2.8 | `PSTRING` for FORTRAN calls C no longer provides escape to pass NULL pointer nor to pass address of original string. PNSTRING introduced with old `PSTRING`'s behavior. PPSTRING introduced to always pass original address of string. Support Alpha/OSF. Document that common blocks used in C should be declared AND defined. | April'93.
3.0 | Automagic handling of ANSI ## versus K&R /**/ preprocessor op. Less chance of name space collisions between `cfortran.h` and other codes. SIMPLE macros, supporting user defined types, have changed names. | March'95.
3.1 | Internal macro name _INT not used. Conflicted with IRIX 5.3. SunOS, all versions, should work out of the box. ZTRINGV_ARGS|F(k) may no longer point to a PDOUBLE or PFLOAT argument. ConvexOS 11.0 supported. | May '95.
3.2 | __hpux no longer needs to be restricted to MAX_PREPRO_ARGS=31. `PSTRING` bug fixed. ZTRINGV_ARGS|F(k) may not point to a PBYTE,PINT,PLONG or PSHORT argument. (P)ZTRINGV machinery improved. Should lead to fewer compiler warnings. (P)ZTRINGV no longer limits recursion or the nesting of routines. SIMPLE macros, supporting user defined types, have changed slightly. | Oct. '95.
3.3 | Supports PowerStation FORTRAN with Visual C++. g77 should work using f2cFortran, though no changes made for it. (PROTO)CCALLSFFUN10 extended to (PROTO)CCALLSFFUN14. FCALLSCFUN10 and SUB10 extended to FCALLSCFUN14 and SUB14. | Nov. '95.
3.4 | C++ supported, but it required the reintroduction of PROTOCCALLSFSUBn for users. HP-UX f77 +800 supported. | Dec. '95.
3.5 | Absoft UNIX FORTRAN supported. | Sept.'96.
3.6 | Minor corrections to cfortran.doc. Fixed bug for 15th argument. [Thanks to Tom Epperly at Aspen Tech.] For AbsoftUNIXFortran, obey default of prepending _C to COMMON BLOCK name. FORTRAN calling C with ROUTINE argument fixed and cleaned up. | Oct. '96.
3.7 | Circumvent IBM and HP "null argument" preprocessor warning. | Oct. '96
3.8 | (P)STRINGV and (P)ZTRINGV can pass a 1- or 2-dim. char array. (P)ZTRINGV thus effectively also provides (P)ZTRING. (P)ZTRINGV accepts a (char *) pointer. | Feb. '97
3.9 | Bug fixed for *VVVVV. `f2c`: Work-around for strange underscore-dependent naming feature. NEC SX-4 supported. CRAY: `LOGICAL` conversion uses _btol and _ltob from CRAY's fortran.h. CRAY: Avoid bug of some versions of the C preprocessor. CRAY T3E: FORTRAN_REAL introduced. | May '97
4.0 | new/delete now used for C++. malloc/free still used for C. FALSE no longer is defined by `cfortran.h` . Absoft Pro FORTRAN for MacOS supported. | Jan. '98
4.1 | COMMA and COLON no longer are defined by `cfortran.h` . Bug fixed when 10th arg. or beyond is a string. [Rob Lucchesi of NASA-Goddard pointed out this bug.] CCALLSFSUB/FUN extended from 14 to 27 arguments. Workaround SunOS CC 4.2 cast bug. [Thanks to Savrak SAR of CERN.] | April'98
4.2 | Portland Group needs -DpgiFortran . [Thank George Lai of NASA.] | June '98
4.3 | (PROTO)CCALLSFSUB extended from 20 to 27 arguments. | July '98

['Support' implies these and more recent releases of the respective OS/compilers/linkers can be used with `cfortran.h`. Earlier releases may also work.]

Acknowledgements

- CERN very generously sponsored a week in 1994 for me to work on `cfortran.h`.
- M.L.Luvisetto (Istituto Nazionale Fisica Nucleare - Centro Nazionale Analisi Fotogrammi, Bologna, Italy) provided all the support for the port to the CRAY. Marisa's encouragement and enthusiasm was also much appreciated.
- J.Bunn (CERN) supported the port to PowerStation FORTRAN with Visual C++.
- Paul Schenk (UC Riverside, CERN PPE/OPAL) in June 1993 extended `cfortran.h` 2.7 to have C++ call FORTRAN. This was the starting point for full C++ in 3.4.
- Glenn P.Davis of University Corp. for Atmospheric Research (UCAR) / Unidata supported the NEC SX-4 port and helped understand the CRAY.
- Tony Goelz of Absoft Corporation ported `cfortran.h` to Absoft.
- Though `cfortran.h` has been created in my 'copious' free time, I thank NSERC for their generous support of my grad. student and postdoc years.
- Univ.Toronto, DESY, CERN and others have provided time on their computers.
- The HTML version of the `cfortran.h` documentation has been made by Olivier Couet `Olivier.Couet@cern.ch`.

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                                                  Burkhard Burow
                                                  burow@desy.de

P.S. Your comments and questions are welcomed and usually promptly answered.
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