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Almost Always Unsigned

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Re: Almost Always Unsigned

#11

Post by StellarScience »

dataflown wrote: post #9

Stroustrup recommends int over unsigned. Dijkstra recommends int over unsigned. Google coding guidelines recommend int over unsigned. Blogger recommends unsigned over int. Tough choice.

I liked how the discussion of 'delta = x - y' moved right on to how really you usually want delta = abs(x - y), so let's talk about that instead...

Even beyond Stroustrup, Dijkstra, and Google, this whole panel of C++ luminaries agrees to prefer signed types and explains pretty clearly why:

- 12:12-13:08 - https://www.youtube.com/watch?v=Puio5dly9N8#t=12m12s

- 42:40-45:26 - https://www.youtube.com/watch?v=Puio5dly9N8#t=42m40s

- 1:02:50-1:03:15 - https://www.youtube.com/watch?v=Puio5dly9N8#t=1h2m50s

Re: Almost Always Unsigned

#12

Post by AlotOfReading »

dataflow wrote: post #3

> for (size_t i = size - 1; i Erm... just because you can, doesn't mean you should. Also, what if you want to go down to something other than 0?

I really don't see what's supposedly awful about that loop, but if you want to count down to x instead of 0 you just do:

    for (size_t i = size - 1; i >= x; i--)

Re: Almost Always Unsigned

#14

Post by dataflow »

AlotOfReading wrote: post #12
dataflow wrote: post #3

> for (size_t i = size - 1; i Erm... just because you can, doesn't mean you should. Also, what if you want to go down to something other than 0?

I really don't see what's supposedly awful about that loop, but if you want to count down to x instead of 0 you just do: for (size_t i = size - 1; i >= x; i--)

> I really don't see what's supposedly awful about that loop

The stopping condition is incredibly confusing and non-obvious. Misleading at first glance, in fact. The whole thing is so unidiomatic that I don't think I've even seen it once in my life. It's a better contender for an underhanded C++ code contest than production code.

> but if you want to count down to x instead of 0 you just do i >= x

No you can't. That fails if x == 0. Which perfectly illustrates why using unsigned everywhere isn't so great. And I say this as someone who likes unsigned types and uses them more than average!

Re: Almost Always Unsigned

#15

Post by StellarScience »

dataflow wrote: post #3

> for (size_t i = size - 1; i Erm... just because you can, doesn't mean you should. Also, what if you want to go down to something other than 0?

> for (size_t i = size - 1; i Agreed, seeing that example briefly made me consider whether this blog post was a parody. Sure, it works for this exact example, by relying on i wrapping "down" to MAX_INT on the last iteration. But how long will it take the next developer who works on the code base to figure that out? Will they figure it out before or after committing changes that break it? Or worse yet, before or after shipping code?

Re: Almost Always Unsigned

#16

Post by StellarScience »

AlotOfReading wrote: post #12
dataflow wrote: post #3

> for (size_t i = size - 1; i Erm... just because you can, doesn't mean you should. Also, what if you want to go down to something other than 0?

I really don't see what's supposedly awful about that loop, but if you want to count down to x instead of 0 you just do: for (size_t i = size - 1; i >= x; i--)

> I really don't see what's supposedly awful about that loop

Exactly! That's precisely the problem with it.

(Hint: think about your code when size = 0.)

Re: Almost Always Unsigned

#17

Post by jandrewrogers »

scared_together wrote: post #4

There was a related article from the other side of the debate a while back: https://news.ycombinator.com/item?id=47989154 It’s pretty sad that after all these years, dealing with fixed size integers is still so complicated. Yes, many of the problems are specific to low level languages with undefined behaviour and numeric for loops. But the issue of subtracting two numbers and possibly having an underflow is both comm…

The issue is that you need dozens of minor variants for the myriad cases involving integers, especially in C. That namespace becomes rather busy.

This particular idiom for finding the absolute difference of an unsigned integer pair is pretty clean and rarely needed. In most contexts you know that one argument will always be greater than or equal to the other, so a simple subtraction will do.

Re: Almost Always Unsigned

#18

Post by Groxx »

dataflown wrote: post #9

Stroustrup recommends int over unsigned. Dijkstra recommends int over unsigned. Google coding guidelines recommend int over unsigned. Blogger recommends unsigned over int. Tough choice.

signed overflow (or underflow) is frequently undefined behavior. (often because it's undefined in C)

unsigned is frequently defined. (often because it's defined in C)

tough choice.

(honestly I just lean towards "over/underflow should raise unless explicitly allowed", the ratio of unintended to intended-and-fully-checked overflow behavior is almost certainly FAR beyond 100:1)

Re: Almost Always Unsigned

#19

Post by tialaramex »

gumby wrote: post #10
tialaramex wrote: post #5

Should be (2022) apparently - surely if HN can automatically screw up titles for various reasons, we can have it add dates automatically [and sometimes get those wrong] too? DanG ? > for instance C and C++ leave signed integer wrap undefined I'm pretty sure the way to write what was meant here is "C and C++ leave signed integer overflow undefined". Wrapping would be a definite choice. Overflow is the situation we're…

> for instance C and C++ leave signed integer wrap undefined Not in C++29, and I think the big 3 compilers (gcc, clang, MS) will have squashed this long before that version is officially approved.

> Not in C++29

C++ 29 doesn't yet exist. It'll be finalised in (as its name suggests) 2029. Are you referring to some proposal you think has been accepted? Or is this one of those "I have concepts of a proposal?" ideas where you confused wishful thinking with reality ?

Re: Almost Always Unsigned

#20

Post by nazcan »

StellarScience wrote: post #11
dataflown wrote: post #9

Stroustrup recommends int over unsigned. Dijkstra recommends int over unsigned. Google coding guidelines recommend int over unsigned. Blogger recommends unsigned over int. Tough choice.

I liked how the discussion of 'delta = x - y' moved right on to how really you usually want delta = abs(x - y), so let's talk about that instead... Even beyond Stroustrup, Dijkstra, and Google, this whole panel of C++ luminaries agrees to prefer signed types and explains pretty clearly why: - 12:12-13:08 - https://www.youtube.com/watch?v=Puio5dly9N8#t=12m12s - 42:40-45:26 - https://www.youtube.com/watch?v=Puio5dly9N8…

Thanks for the excerpts! I was trying to understand the reasoning, which seem to just be in the 2nd excerpt:

- The rules of signed/unsigned are complicated and there is too much auto-conversion - does that mean languages that make this more explicit means this is fine? It just seems ideal to have stronger typing. - It is mentioned that you can initialized an unsigned int to "-2" - but that presumably could also be fixed in the language.

I'm trying to separate out which is "don't do this in C/C++" and which is "don't do this in any language".

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