On Sun, 3 Jun 2001, James Dennett wrote:
> >
> > Section 3.6.1.5 - 'If control reaches the end of main without encountering a
> > return statement, the effect is that of executing return 0;'
> >
> > But why? That's what I want to know.
>
> It does have the desirable effect of removing one commonly
> invoked piece of undefined behaviour from the Standard; it
> has been very common for sloppy users to fail to return a
> value from main.  (It has the undesirable effect of
> introducing an inconsistency, in that main is the only
> function to which this applies.)
>
> I don't know if that was the reason for the change though,
> as I was not part of the Standardisation process when the
> rule was written.

It was (and still is) common for implementations not to need a
return statement in main, even in C programs. "Falling off the end"
of main has the effect of returning a status of success. Some other
systems do not use the return value at all, and the returned value
is not meaningful.

C++ originally required a return statement in main. There were many
complaints from users who had to add return statements to satisfy
compilers, even though the system never needed the return statement.

Although I favored this language change when it was proposed (I
think in 1992), I have since thought that it might better have
been left as a quality-of-implementation issue. As with other
unportable features, a compiler could optionally warn about a
missing return statement, rejecting the code in "pedantic" mode.

Of course, a compiler is currently allowed to warn about a missing
return statement (because a compiler can warn about anything at all.)

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