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From: jsdy@hadron.UUCP (Joseph S. D. Yao)
Newsgroups: net.lang.c,net.unix
Subject: Re: return() vs. exit() vs. _exit()
Message-ID: <202@hadron.UUCP>
Date: Sun, 26-Jan-86 14:07:01 EST
Article-I.D.: hadron.202
Posted: Sun Jan 26 14:07:01 1986
Date-Received: Thu, 30-Jan-86 04:51:08 EST
References: <178@rexago1.UUCP>
Reply-To: jsdy@hadron.UUCP (Joseph S. D. Yao)
Distribution: net
Organization: Hadron, Inc., Fairfax, VA
Lines: 42
Xref: watmath net.lang.c:7690 net.unix:6959
Summary: return ~= exit > _exit

In article <178@rexago1.UUCP> rich@rexago1.UUCP (K. Richard Magill) writes:
>What's the difference between leaving main by return() vs exit() vs _exit()?

Functionally, return and exit should be identical.  Your 'lint'
(s5r2.0v2) prob'ly complains if you use exit() tho.  The code goes
roughly like:
[C header, crt0.s:]
	push	envp
	push	argv
	push	argc
	call	$3, _main
	push	r0
	call	$1, $_exit
	sys	$exit_system_call
	halt
Note that exit(main(argc, argv, envp)) is the effect.

The exit() code resembles:
exit(val)
  int val;
{
	register FILE *fp;

	for (fp = _iob; fp < &_iob[NIOBUFS]; fp++)
		if fp has been opened
			fclose(fp);
	_exit(val);
}
..........
__exit:
	move	arg to r0
	sys	$exit_system_call

Shared and local memory are reclaimed by the kernel after an exit()
system call.

>                               ...  What is a gate 4, 8?

Got my curiosity piqued.
-- 

	Joe Yao		hadron!jsdy@seismo.{CSS.GOV,ARPA,UUCP}