new topic...exorcising externs

[Andrew Klossner]

[]

	"There are a number of situations where externals are both
	cleaner and more convenient than parameter passing.  One
	instance that comes to mind is "errno".  I wouldn't hold it up
	as the paradigm of clean design, but it beats passing a pointer
	to an error value to every system call."

The "well structured" approach would be to define a small module (aka
package) with entry points as follows:

	void seterrno(i) int i;

		/* called by system routines to record an error number */

	int geterrno()

		/* returns the last parameter to seterrno, 0 if none */

Now you do your system calls as follows:

	if (open(...) == -1) {
		printf("open error %d\n", geterrno());
		}

Presto, no externals, just a single static within the errno module.
This would make a lot more sense if the loader supported more than just
a flat global name space, a la Modula II.

  -- Andrew Klossner   (decvax!tektronix!orca!andrew)      [UUCP]
                       (orca!andrew.tektronix at rand-relay)  [ARPA]