VAX VMS C / UNIX C Compatibility --

[eric]

> >Another thing I'm looking for under VMS is the ability to load both
> >C and FORTRAN object files into one executable. Does anyone know if
> >this works?
> 
> It is supposed to but some while ago, there was a discussion on 
> INFO-VAX saying that C in some way violated the VMS procedure calling
> standard. Thus there is one or more obscure case that fails. This
> is ironic in that the calling standard is highly touted by DEC. This 
> discussion predated VMS4, so they may have fixed it.

I don't know if I would make too much of this.  The procedure calling
calling standard is only that and nothing more.  The fact that I can
violate the standard in C, is just a function of the fact that I can
do most anything in C.  I can violate the standard by doing certain
things in MACRO also, so this is just another example of "I can do
anything in C that I can do in MACRO".  There are rather simple
rules to follow if you are programming in C and are interfacing to
other languages to make a program comply with the procedure calling
standard.  Note that there is no problem if a program is entirely
written in C, so that this problem will not effect the porting
of existing C programs.

> There is also a general rule that happens to apply in this case, that
> I/O can only be done from routines in the same language as the main. 
> This is because that is where most compilers on most machines put the
> calls to the I/O system initializers, and few languages share I/O 
> systems. On some machines, you can't even do it if there are routines
> of another language between the main and the routine in question.

This may have been the case in an old version of VMS, but it certainly
isn't correct now.  I regularly mix FORTRAN and PASCAL I/O, and I just
verified that I can do C standard I/O mixed with PASCAL I/O.  In VMS
run-time systems, initialized data is linked in the run-time libraries
as initialized copy-on-reference data, and so no initialization needs
to be done at run time.  The biggest problem one is likely to run
into when mixing I/O to the terminal is that FORTRAN, PASCAL, and C
all have different ideas about carriage control, and each maintains
a separate picture of what carriage control characters are necessary.

> Terry Poot
> Nathan D. Maier Consulting Engineers
> (214)739-4741
> Usenet: ...!{allegra|ihnp4}!convex!smu!ndm20!tp
> CSNET:  ndm20!tp at smu
> ARPA:   ndm20!tp%smu at csnet-relay.ARPA

In general, C programs that do I/O with standard I/O library
interfaces (getc, printf, etc...), use math library functions, and
that don't use things like stat and ioctl can be expected to work
unmodified on VMS systems.  Programs that use (read, write, open, creat)
will work in many cases, although they will have to be looked at
carefully.  In particular, the file formats may cause a problem.
Programs that rely on forking/vforking and pipes will probably
need major changes to run.  DEC supplies an implementation of
vfork and pipes, but it is so limited that I suspect it may not
be useful.  Still, if your program happens to fall within the
limitations, it may run, although with a severe performance problem.
There are many miscellaneous routines supplied for compatabilility with
UNIX, and if a program uses them, there is a large chance it will
work for both UNIX and VMS.  This compatability has expanded a lot
in the last release of the C compiler and I have not had a chance
to fully explore the new stuff.  It looks like there is even a
curses.

					Eric G. Stern
					Dept. of Physics SUNY StonyBrook
					stern at bnl.arpa
					stern at bnl.bitnet
					stern at bnldag.bitnet
					...!philabs!sbcs!bnl!stern