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Mildly interesting quirks of C

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Re: Mildly interesting quirks of C

#41

Post by blep_ »

veltas wrote: post #4

"Flat Initializer Lists" is given as an example in K&R C I think, at least the first edition, when writing those extra braces to fill out an initializer must have felt very redundant. These days many compilers will warn if you do this, however, as it is rare people do this and usually indicates a misunderstanding of the type used. I think it's quite readable though, so it's a shame it causes warnings. What do you thi…

I find it slightly worse to read. It's C, so my brain is in "newlines don't matter" reading mode, so I see an array of 6 things and then have to mentally split them back up.

Re: Mildly interesting quirks of C

#42

Post by tmtvl »

PointyFluff wrote: post #23

As someone who's moved on to Rust, I see this as one long list of nightmares.

I also see a fair few elements on that list as being problematic, to say the least. Can't stand Rust, though, so for those times I really need high performance I try and keep my C knowledge sharp-ish.

Fortunately GCC has a whole bucket-list of warnings that can be enabled (I like compiling with -Wall -Wextra -pedantic, myself) which can, combined with proper tooling, catch many issues.

Re: Mildly interesting quirks of C

#43

Post by blep_ »

unnouinceput wrote: post #37
Jorengarenar wrote: post #36

Earlier quoted context omitted.

"Dynamic array" refers to block of memory allocated via malloc() which you just happen to use as array. "Flexible array member" [0] is when you have a struct and its last member is an array with unspecified size. An example: #include #include struct Foo { int len; int* arr; // dynamic "array" }; struct Bar { int len; int arr[]; // FAM }; int main() { const int n = 12; // have to allocate myself; no guarante it will b…

>"Dynamic array" refers to block of memory allocated via malloc() which you just happen to use as array. No. A dynamic array is an array which can be expanded or shrinked during its runtime life. The fact that C/C++ uses malloc for that (and btw, it's not the only way to do it) it's her problem. In other languages you have dynamic arrays that can be expanded/shrinked without using an extra line - main reason why nowa…

It has to be last because it's not a pointer to the array, it is the array. The array elements are immediately after the struct in memory. You can't resize it without reallocating the whole struct.

Re: Mildly interesting quirks of C

#44

Post by guenthert »

> UB is impossible

What? UB is clearly undesirable, but assuming it is impossible and deducing other outcomes must be meant are clearly wrong assumptions by the compiler writer.

More sensible compilers (including older version of clang) do the right thing (TM) here and yield a compiler error.

There were earlier attempts at do-what-i-mean programming languages. They are rightfully buried in history.

Re: Mildly interesting quirks of C

#45

Post by [deleted] »

plq wrote: post #15

Whenever the subject of C/C++ quirks is brought up, I always like to point out the Deep C/C++ presentation: http://www.pvv.org/~oma/DeepC_slides_oct2011.pdf Source: https://freecomputerbooks.com/Deep-C-and-Cpp.html#downloadLi... Previous discussion: https://news.ycombinator.com/item?id=3093323 It could be considered a bit dated at this point (It's before C++11) but I find it still both entertaining and educating.

[deleted]

Re: Mildly interesting quirks of C

#46

Post by cptnapalm »

jwilk wrote: post #18
fb03 wrote: post #16

My favorite C "quirk": If you have an array and you want to access an item of it, you can swap the variable and the index number (put the variable name inside brackets and the number outside): a[5] is the same as: 5[a] why? a[5] is actually sugar for *(a + 5), so by commutative property, you can also do *(5 + a) to access the same memory position :-)

That's #15 on the list.

&(list + 15) = https://gist.github.com/fay59/5ccbe684e6e56a7df8815c3486568f...

Re: Mildly interesting quirks of C

#47

Post by [deleted] »

still_grokking wrote: post #40

After learning about a few of these I started to understand why people coming from C always said that PHP is a well designed language… But OK, I understand that my mind is just not made for the complexity of C. Most likely I'm not a real programmer. I get instantly knots in my brain and start to bang my head against the wall when I need to look for too long on C code. Actually even C documentation is enough to trigge…

[deleted]

Re: Mildly interesting quirks of C

#48

Post by cvoss »

guenthert wrote: post #44

> UB is impossible What? UB is clearly undesirable , but assuming it is impossible and deducing other outcomes must be meant are clearly wrong assumptions by the compiler writer. More sensible compilers (including older version of clang) do the right thing (TM) here and yield a compiler error. There were earlier attempts at do-what-i-mean programming languages. They are rightfully buried in history.

UB is not impossible; I think the author is being a little cheeky there. But the standard does grant compilers extreme liberties as far as how they deal with programs which can execute UB. LLVM's choice of what to do with that liberty, in this case, seems to be to assume the UB is unreachable and continue legally optimizing the program under that assumption. That's not a wrong assumption according to the definition of C.

It's debatable whether it's a good assumption. But not wrong.

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