[perl4ever]

"This document imposes no requirements on the behavior of programs that contain undefined behavior."

The NY Vehicle and Traffic law imposes no requirements on the behavior of drivers who engage in cannibalism. However, it would be odd to interpret this as meaning that if you commit cannibalism, you are exempt from all rules regarding motor vehicles.

There are clearly two kinds of "undefined" behavior - the kind that is defined as undefined, and the kind that is not. To understand either, you have to understand both.

[MauranKilom]

> The NY Vehicle and Traffic law imposes no requirements on the behavior of drivers who engage in cannibalism.

Are you trying to argue that the standard quote is unclear? That you think it can be read "imposes no additional/special requirements" (because that's the interpretation that your traffic law argument assumes)? Because if you ignore the nonsensical meaning, I would read your traffic law sentence as "imposes no requirements whatsoever".

Regardless of what your stance is regarding possible ambiguity in the way that sentence is worded, both the intent and the practical consequences of that statement are abundantly clear: If your program has UB (per what the C++ standard considers UB), then the C++ standard makes absolutely no guarantees what will happen when you run it.

> There are clearly two kinds of "undefined" behavior - the kind that is defined as undefined, and the kind that is not. To understand either, you have to understand both.

I don't understand what you are trying to say. There is only one kind of undefined behavior. If you follow the rules of the C++ standard you get to live in a nice and predictable world. If you don't, anything can happen and you're on your own.

[perl4ever]

There's more than one kind of undefined behavior, and probably more than one way to categorize it.

The distinction I was making is between "what the...standard considers UB" and what the standard doesn't consider period. For instance, the standard doesn't (I assume) declare anything about the effect of cosmic rays on C++ programs. However, that does not mean that C++ compilers are designed or should be designed not to work unless run on equipment that is completely shielded.

There is a semantic difference that seems important to me, but which continually slips away in these discussions. And it's palpably related, for me, to the issues people have with compiler behavior. It's not totally the standard at issue, I don't think, but the culture that provides its context.

It would be nice if following a language standard meant that you get to live in a nice and predictable world, but isn't this an absurd statement?