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From: Keith Thompson <Keith.S.Thompson+u@gmail.com>
Newsgroups: comp.lang.c++
Subject: Re: Has "stack overflow" specified behavior?
Date: Mon, 13 Dec 2021 15:55:16 -0800
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Xref: csiph.com comp.lang.c++:82616

wij <wyniijj@gmail.com> writes:
> void t() {
>   int a;
>   ++a;
>   t();
> };
>
> int main()
> {
>  t();
> }
>
> ---
> Has "stack overflow" specified behavior?

The standard does not specify what happens when a resource limit is
exceeded.  In my opinion that matches the standard's definition of
"undefined behavior" (behavior that is not defined).

Is the variable `a` intended to track the depth of the recursion?  It
doesn't.  A new instance of `a` is created every time t is called.  You
didn't initialize `a`, but if you initialized it to 0 then `++a` would
simply set it to 1.

If you made `a` static, it would count the depth of the recursion -- and
you'd have undefined behavior after the value of `a` reaches INT_MAX.

With `a` defined as you did here, there's a distinct instance of `a` for
each call to t, and each instance has its own distinct address, a value
of type int*.  There can be at most 2**(CHAR_BIT * sizeof (int*))
distinct int* values.  If you never refer to the value or address of `a`,
an optimizing compiler is likely to eliminate it and change the
recursive call to a loop, but that doesn't apply in the abstract
machine.  See N1570 5.1.2.3 "Program execution":

    The semantic descriptions in this International Standard describe
    the behavior of an abstract machine in which issues of optimization
    are irrelevant.

In the abstract machine, each instance of `a` occupies sizeof (int) bytes
and has a unique address of type int*.  After optimization, `a` might not
exist.

-- 
Keith Thompson (The_Other_Keith) Keith.S.Thompson+u@gmail.com
Working, but not speaking, for Philips
void Void(void) { Void(); } /* The recursive call of the void */