Comment by btilly | Hacker News Reader

Comment by btilly | Hacker News Reader

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Which attitude?

The attitude that undefined behavior is seen as an opportunity for optimization, and backwards compatibility with your installed base is not particularly important. Not even if you know that the change breaks code in the wild which was intended for security checks.

See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=30475 for discussion around one such change.

I will elide the specific self-congratulatory attitudes that you claim to have, and your not so subtle insults to myself. With one exception.

Or maybe you are talking about the attitude of not assuming that all users know the C standard to the letter and never write code that has bugs ?

This is exactly the reverse of the attitude that I've observed.

Including in yourself 2 posts up when you described how hard it can be to decide whether something is undefined behavior, but if it is undefined behavior then it isn't a compiler bug. Which, as a developer, tells me that I definitely am not able to decide whether the code will do anything like what appears to be written, or I will get unexpected nasal demons, in some unrelated section of code.

> The attitude that undefined behavior is seen as an opportunity for optimization

When you choose to write C, you are accepting the contract that if your program has UB, there are no guarantees about what it does.

If you can't uphold your end of the contract, C is not for you.

There is a huge difference between complaining that this contract is too hard to uphold, which is a complain that you should take with the C standard, and complaining to the compiler that, on contract violation, your program misbehaves.

If you can't accept that, again, C is not for you.

For every novice that complains about their mistake misbehaving I have 100 expert C programmers that would complain about bad codegen for programs that do uphold the contract.

From a compiler writer perspective, it is impossible to argue that we should penalize those that take the time and experience to play by C rules in favor of those that write broken programs.

100% of the experts would agree that it is hard to write correct code, but "disabling compiler optimizations" is not the right place to fix that.

If you believe that's the case, you are free to compile all your code with -O0, use volatile everywhere, or just use Python or some other language that suits you best.

But the argument that you are making is ridiculous. You don't like the consequences of breaking the law, so your conclusion is that prisons should be 5 star hotels and all the law-abiding tax-payers should finance them so that you enjoy them at their cost. I wish you the best luck in life with that attitude mate.

Gee, it didn't take you long to revert to form, did it? I will just respond to the most important bits.

When you choose to write C, you are accepting the contract that if your program has UB, there are no guarantees about what it does.

Back when I started programming, C was widely understood as having a very different contract. Namely, "It is a very simple language with no guard rails, but describes exactly what the computer will do." This was the language as describe in K&R.

The contract that you describe was something that compiler writers came up with long after the language was in wide adoption. Based on my anecdotal impression, it also wasn't the direction that most of said user base was asking for. And it is the opposite of the direction that most other languages have gone.

If you can't uphold your end of the contract, C is not for you.

Which is what I said from the start. My exact words were, "As a developer, this attitude on the part of C compiler writers is a reason to avoid C and C++."

I generally am fine in slower languages like Python, JavaScript, SQL, Go, etc. The next time that I need performance, I will look into Rust. Isn't this exactly what you think that I should do?

But the argument that you are making is ridiculous. You don't like the consequences of breaking the law, so your conclusion is that prisons should be 5 star hotels and all the law-abiding tax-payers should finance them so that you enjoy them at their cost. I wish you the best luck in life with that attitude mate.

You know, if you argue with what I said rather than what you think I said, you might make more sense. Again, here is what I said:

"The actual semantics of the language are effectively impossible for a non-expert to tell from the code as written and operating. And what you don't know can hurt you. That's like juggling caltrops with bare hands - you're guaranteed to get hurt."

Given the level of care and knowledge which is required to identify undefined behavior, the first sentence is true. Given how much compiler authors value squeezing more performance over backwards compatibility, so is the second. The third is the logical result of the first two.

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