Path: utzoo!mnetor!uunet!husc6!cmcl2!brl-adm!umd5!mimsy!chris
From: chris@mimsy.UUCP (Chris Torek)
Newsgroups: comp.unix.questions
Subject: Re: exit(main(argc,argv,env));
Message-ID: <9875@mimsy.UUCP>
Date: 18 Dec 87 21:59:09 GMT
References: <10875@brl-adm.ARPA> <1451@houdi.UUCP> <2058@bloom-beacon.MIT.EDU>
Organization: U of Maryland, Dept. of Computer Science, Coll. Pk., MD 20742
Lines: 52

As various people have pointed out, crt0.c (the file in which the

	exit(main(argc, argv, env))

call was found) is a system dependent way of getting C code started.
(When the operating system is asked to run a program, it jumps to
some starting location with registers and/or stack set up in some
particular way.  The code at this start location has to turn this
into a normal C stack frame and call main.  In most Unixes, this is
done by a routine in crt0.s or crt0.c.)

Nonetheless, exit(main(argc, argv, env)) is a perfectly legal thing
to write.  Here is an example with the env parameter deleted:

	int
	main(argc, argv)
		int argc;
		char **argv;
	{
		int n;

		/*
		 * Compute and print the factorial of all arguments.
		 */
		if (argc < 2)
			return (0);	/* no arguments */

		/* do the first argument */
		n = atoi(argv[1]);
		printf("%d! = %d\n", n, fac(n));

		/* do the rest of the arguments */
		exit(main(argc - 1, argv + 1));
	}

	int
	fac(n)
		int n;
	{

		if (n < 2)
			return (1);
		return (n * fac(n - 1));
	}

The *only* thing that is special about `main' is that the runtime
system somehow calls it to start the program, and that when it
returns to the runtime system (if ever), the `int' value it returns
is given back to the system as a status value.
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7690)
Domain:	chris@mimsy.umd.edu	Path:	uunet!mimsy!chris