Comparing HP C and HP FORTRAN 77

Mixing C and FORTRAN File I/O

A FORTRAN unit cannot be passed to a C routine to perform I/O on the associated file. Nor can a C file pointer be used by a FORTRAN routine. However, a file created by a program written in either language can be used by a program of the other language if the file is declared and opened within the latter program. C accesses the file using I/O subroutines and intrinsics. This method of file access can also be used from FORTRAN instead of FORTRAN I/O.

Be aware that HP FORTRAN 77 on HP 9000 workstations and servers using HP-UX uses the unbuffered I/O system calls read and write (described in the HP-UX Reference manual) for all terminal I/O, magnetic tape I/O, and direct access I/O. It uses the system calls fread and fwrite for all other I/O. This can cause problems in programs that mix C and FORTRAN I/O. In particular, C programs that use stdio(3S) output procedures such as printf and fwrite and FORTRAN output statements must flush stdio buffers (by calling the libc function fflush) if they are in use before returning to FORTRAN output or the I/O may be asynchronous (if the library is using write).

Mixing FORTRAN direct, terminal, or tape READ statements with stdio fread input results in the FORTRAN READ commencing from the beginning of the next block after the contents of the buffer, not from the current position of the input cursor in the fread buffer. The same situation in reverse may occur by mixing read with a FORTRAN sequential disc read. You can avoid these problems by using only the read and write calls in the C program that the FORTRAN I/O library uses.

Passing Parameters Between HP C and HP FORTRAN 77

All parameters in HP FORTRAN 77 are passed by reference. This means that all arguments in an HP C call to an HP FORTRAN 77 routine must be pointers. In addition, all parameters in an HP C routine called from HP FORTRAN 77 must be pointers, unless the HP FORTRAN 77 code uses the $ALIAS directive to define the parameters as value parameters. Refer to the example called "HP FORTRAN 77 Nested Structure" later in this chapter.

Passing string variables of any length must be done by: building and passing a two-parameter descriptor (defined in Note 3 above), initializing the string appropriately, and by passing two arguments. The two arguments are the pointer to the characters and the value of the length word. This is shown below:

     char *chars = "Big Mitt";
     int len;
        .
        .
        .
     len = strlen(chars);
 
     pass_c_string (chars, len);
        .
        .
        .

Linking HP FORTRAN 77 Routines on HP-UX

When calling HP FORTRAN 77 routines on an HP-UX system, you have to include the HP FORTRAN 77 run-time libraries by adding the option:

-lcl

to the cc command line.

For details on linking external libraries, see the -l option of the cc(1) and ld(1) commands in the HP-UX Reference manual.