Daniel Levite ([log in to unmask]) wrote:
: does anyone know if you can put a C routine in an XL that can then be
: called from COBOL?
: and can you point me in the direction on where to learn how to do
: this...thaks

For sake of discussion, I'll assume you are talking about COBOL II/iX
and C/iX on MPE/iX 5.0 or later, and that you have the following
manuals.

   1.  HP COBOL II/XL Reference Manual, part number 31500-90001,
       July 1991 edition.
   2.  HP COBOL II/XL Programmer's Guide, part number 31500-90002,
       July 1991 edition.
   3.  HP C/iX Reference Manual, part number 31506-90005,
       June 1992 edition.
   4.  HP C Programmer's Guide, part number 92434-90002,
       August 1992 edition.
   5.  HP C/iX Library Reference Manual, part number 30026-90001,
       October 1992 edition.

The answer is yes, a COBOL program can call a C function that
resides in an XL.  It can be a lot of fun, if you like that sort
of thing.  To some extent, it is even supported.

For some actual sample code showing COBOL calling C, see
pages 4-22 through 4-24 of the COBOL programmer's guide.

There are several things in particular that you need to be aware of.

   1.  You need to understand how both languages store their
       various data types and pass/receive parameters.  Pay
       attention to storage format and alignment.  For COBOL,
       pay attention to the USAGE clause (reference manual,
       pp. 7-64 through 7-68) and the alignment rules
       (page H-22).  If you want to pass pointers, you might
       need the .LOC. pseudo-intrinsic (p. 11-20).  And if you
       want to pass by value, you'll need backslashes in the
       CALL statement (p. 11-15).  Then there's the GIVING
       phrase if you want to receive a function return
       (p. 11-24).

       For C, data types and alignment are documented in the
       reference manual (Chapter 9) and the programmer's guide
       (Chapter 2).

   2.  The C function may not work right unless you turn off
       COBOL traps.  For a discussion of the COBOL trap
       mechanism and how it relates to other languages,
       read pp. H-33 through H-38 of the COBOL reference
       manual.  Be sure to turn COBOL traps back on as
       soon as you return from the C function.

   3.  If the C function does any output using the C library,
       remember that buffered output won't be automatically
       flushed when the program terminates, since the outer
       block won't be in C.  You will want to explicitly
       flush the output, close the files, or use unbuffered
       I-O.

There are some other potential pitfalls, but this should get
you started.  Have fun!

Walter Murray
Hewlett-Packard
Support Technology Lab