From Newsgroup: comp.lang.c

Keith Thompson <Keith.S.Thompson+u@gmail.com> writes:

Tim Rentsch <tr.17687@z991.linuxsc.com> writes:

Keith Thompson <Keith.S.Thompson+u@gmail.com> writes:

Andrey Tarasevich <noone@noone.net> writes:
[...]

#include <stdio.h>

struct S { int a[10]; };

int main()
{
struct S a, b = { 0 };
int *pa, *pb, *pc;

pa = &a.a[5],
pb = &b.a[5],
pc = &(a = b).a[5],
printf("%p %p %p\n", (void *) pa, (void *) pb, (void *) pc);
}

This version has no UB.

I believe it does. [...]

If you look again carefully, I expect you will reach a
different conclusion.

Please explain. Or don't.

I explained, in text that you snipped, why I think it has UB.
If there's a flaw in my reasoning, I invite you to point it out
without being mysterious.

I wasn't thinking about your reasoning or what flaw there may have
been in it. My intention was to suggest a course of action that
would be helpful rather than to point out any sort of mistake. But
since you ask, I think the mistake you made was jumping to a
conclusion without looking carefully enough at the problem.
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From Newsgroup: comp.lang.c

Tim Rentsch <tr.17687@z991.linuxsc.com> writes:

Keith Thompson <Keith.S.Thompson+u@gmail.com> writes:

Tim Rentsch <tr.17687@z991.linuxsc.com> writes:

Keith Thompson <Keith.S.Thompson+u@gmail.com> writes:

Andrey Tarasevich <noone@noone.net> writes:
[...]

#include <stdio.h>

struct S { int a[10]; };

int main()
{
struct S a, b = { 0 };
int *pa, *pb, *pc;

pa = &a.a[5],
pb = &b.a[5],
pc = &(a = b).a[5],
printf("%p %p %p\n", (void *) pa, (void *) pb, (void *) pc);
}

This version has no UB.

I believe it does. [...]

If you look again carefully, I expect you will reach a
different conclusion.

Please explain. Or don't.

I explained, in text that you snipped, why I think it has UB.
If there's a flaw in my reasoning, I invite you to point it out
without being mysterious.

I wasn't thinking about your reasoning or what flaw there may have
been in it. My intention was to suggest a course of action that
would be helpful rather than to point out any sort of mistake. But
since you ask, I think the mistake you made was jumping to a
conclusion without looking carefully enough at the problem.

The mistake I made was failing to notice that the line with the
assignment to pc ends with a comma operator rather than a semicolon.

The code was deliberately obfuscated, and I fell for it.

I acknowledged that nearly a year ago. Why bring it up now?
I find it extremely annoying.
--
Keith Thompson (The_Other_Keith) Keith.S.Thompson+u@gmail.com
void Void(void) { Void(); } /* The recursive call of the void */
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