From: utzoo!decvax!genradbo!mitccc!zrm
Newsgroups: net.unix-wizards
Title: Re: Information on Unix/Vax peculiarities
Article-I.D.: mitccc.198
Posted: Sun Nov 28 14:42:41 1982
Received: Mon Nov 29 02:25:24 1982
References: sri-unix.4448

Well, it would take too long to list all the possible machine dependencies
possible with C compiler instantiations, but perhaps some general
philosophy of C might help.

o In general, you want to be able to cast *anything* to int. This means
  an int ought to be the same size as a pointer. Berkley, and Whitesmith's
  do this correctly in their compilers, Alcyon does it wrong.

o Muddling about inside larger objects should be done with unions. However,
  in the program CHUQUI mentioned, the author seems to have been ingenious
  enough to scuttle all portability -- he probably assumes ints hold
  exactly two bytes. Note that using unions also insures tha byte ordering
  within a larger word won't matter from machine to machine (assuming
  the compiler isn't broken). There is also a rather rude hack you can
  use where you declare and array

	struct
	{
		char hibyte;
		char lobyte;
	}

  and use the members of that structure to reference parts of a two-byte
  object with the syntax

	WORD foo;		/* WORD is a defined type, another
				   very useful tool */
	high = foo.hibyte;	/* BLETCH! */

  but this is really horrid style and would rather use RPGII than actually
  maintain code like that.

o A fix that might work for CHUQUI is using defined types. But you have
  to be very careful on several counts.

  > If you substitute, say, WORD for int, on a wholesale basis, you have
    to make sure no pointers are being put in ints.

  > All parameters passed to functions are of size sizeof(int). Treat
    parameters essentially as you would registers.

All this is making me queasy. There are all sorts of other nasty little
things you can trip over on your way from one machine (or compiler)
to the next and the ony way to verify portability is to port something
and fix it when it breaks.

Indigestion!
Zig