hxhxhrra
For other cases (e.g. aliasing, alignment), I'd agree that one is rather safe as long as the dangerous tools (e.g. reinterpret_cast) are not used.
You may dislike it, but that is not how UB in C and C++ works. See [1] for a guide to UB in C/C++ that may already have been posted elsewhere here.
It is a common misconception that UB on a particular operation means "undefined result", but that is not the case. UB means there are no constraints whatsoever on the behavior of the program after UB, often referred to as "may delete all your files". See [2] for a real-world demo doing that.
[1] https://blog.regehr.org/archives/213
[2] https://kristerw.blogspot.com/2017/09/why-undefined-behavior...
This has caused a Linux kernel exploit in the past [1], with GCC removing a null pointer check after a pointer had been dereferenced. Null pointer dereferences are UB, thus GCC was allowed to remove the following check against null. In the kernel, accessing a null ptr is technically fine, so the Linux kernel is now compiled with -fno-delete-null-pointer-checks, extending the list of differences between standard C and Linux kernel C.
I discovered the main results of my PhD thesis essentially as follows:
1. Find complicated construction A, hoping to prove some new results.
2. Fail to sufficiently understand/analyze A.
3. Write computer program to analyze characteristics of A for small n.
4. Using OEIS, discover that apparently A is (in some sense) equivalent to some completely different construction B, which is much simpler and well-understood.
5. Show desired result as well as further other results using B and variations of it.