From mboxrd@z Thu Jan  1 00:00:00 1970
From: rinku rathore <rinku_ques@yahoo.com>
Subject: Re: exit(42)
Date: Sat, 25 Sep 2004 03:57:36 -0700 (PDT)
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To: Micha Feigin <michf@post.tau.ac.il>
Cc: linux-c-programming@vger.kernel.org


--- Micha Feigin <michf@post.tau.ac.il> wrote:

> On Fri, Sep 24, 2004 at 12:57:59PM +0100, Ankit Jain
> wrote:
> > well do any body know what does this mean?
> > 
> > exit(42)
> > 
> 
> It means return value 42 as the exit value for the
> program. Every
> program returns an exit value (integer) when it
> exits. 0 means not
> error, anything else is an error value and the
> specific number can mean
> the type of error if its documented and the caller
> knows what to expect.
> 
> > and also when we say exit(0) or exit(1) then there
> is
> > anyway to catch these values
> > 
> 
> From the caller you can catch this value, read the
> documentation for
> your shell about the return value. I think its $?
> under bash.
> 
> > also when we return from main fn then what is the
> > benfit?
> > 
> > does it have any utilisation?
> > 
> 
> main is just another function almost like any other
> in your
> program. The system doesn't look for the function
> main to run, its just
> a convention used by c (in windows the main function
> is called winmain
> for example, don't remember what its called in
> pascal, but IIRC
> something different also).
> 
> when you compile your program its linked with some
> assembler code that
> handles setting up you environment. The system looks
> for a symbol in
> your program called _start and start the execution
> from there. This
> function is responsible for setting everything up,
> including argc and
> argv (the command line arguments and environment
> variables) and possibly
> handling calling constructors of global classes in
> c++ (not sure about
> that though). It then calls your main function with
> the proper values
> of argc and argv.
> 
> When you main function returns, or when you call
> exit, a function called
> exit is called which handles all the cleaning up of
> your program and
> then the function _exit is called to finish exiting
> the program. You
> are not supposed to call _exit directly since it
> bypasses cleaning up,
> calling it directly is only useful if you use vfork
> where you don't
> want any cleaning up done since it messes things up
> (you shouldn't use
> vfork for most things nowadays since fork has almost
> no more
> overhead. If you don't know you need it, then you
> don't).
> 
> > thanks
> > 
> > ankit
> > 
> >
>
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> 
this could also be the reason:
if we r working with child and parent procees then as
child get terminated it has to pas some status to the
parent that is going to exit then by using exit(42)
child give information to the parent that it is goig
to exit now having status 42.

thanx


		
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