Hacker News Reader

I feel like that's very well covered already when I wrote:

"The semantics of undefined behaviour are exactly the same before and after any transformation of the program"

[emphasis added]

I think you've got this idea that Undefined Behaviour somehow means that the behaviour is defined but is being kept secret from you. It isn't. The behaviour really is Undefined. Doing further transformations to it is therefore always harmless.

View on HN

So how does a computer cause “undefined” behavior to occur? Does it invoke the “undefined” opcode? Of course not. A computer executing a program that has entered UB will do something specific but not specified in the standard.

I don’t think you are getting that Undefined is a concept in the language specification domain, that is not literally implemented. Consequently, you don’t even see yet what my question is about. When I think of a way to make it clearer, I will follow up.

UB can not be relied upon as the compiler can do arbitrary transformations to the code. Relying on it will cause security issues or head scratching bugs down the line.

Yes, yes, yes, we all know this. That is not what this thread is about. By replying to one comment in isolation, you are completely missing the context. For clarification of what it is about, read the rest of the thread.

Reply on news.ycombinator.com