C: Simple Defer, Ready to Use • Hacker News Board

Re: C: Simple Defer, Ready to Use

#31

Post by accelbred » Mon, Jan 06, 2025, 8:07 PM UTC

uecker wrote: post #26

accelbred wrote: post #15

Unfortunately, this requires an executable stack, and only works on gcc, though an alternate implementation can work on clang. After a few attempts at defer, I ended up using a cleanup macro that just takes a function and a value to pass to it: https://github.com/aws-greengrass/aws-greengrass-lite/blob/8... Since the attribute or a function-like macro in the attribute position broke the c parsing in some tooling, I m…

It does not need an executable stack: https://godbolt.org/z/K1GTa4jh4

The macro from the article uses nested functions which on gcc are implemented with tramolines that need executable stack.

https://thephd.dev/lambdas-nested-functions-block-expression...

Re: C: Simple Defer, Ready to Use

#32

Post by uecker » Mon, Jan 06, 2025, 8:08 PM UTC

accelbred wrote: post #31

uecker wrote: post #26

Earlier quoted context omitted.

It does not need an executable stack: https://godbolt.org/z/K1GTa4jh4

The macro from the article uses nested functions which on gcc are implemented with tramolines that need executable stack. https://thephd.dev/lambdas-nested-functions-block-expression...

The trampolines are not generated in this case.

Re: C: Simple Defer, Ready to Use

#33

Post by vkazanov » Mon, Jan 06, 2025, 8:08 PM UTC

worik wrote: post #27

Does C really need this? Do languages need to grow in this way? The overriding virtue of C is simplicity.

Yes it does, and numerous projects already use variants of this trick.

Re: C: Simple Defer, Ready to Use

#34

Post by hollerith » Mon, Jan 06, 2025, 8:09 PM UTC

sigzero wrote: post #30

marmaduke wrote: post #8

Earlier quoted context omitted.

i like how the contraction it’s and abbreviation T’is are anagrams

It is not T'is, it is Tis. No apostrophe.

I've only ever seen it spelled 'tis

Re: C: Simple Defer, Ready to Use

#35

Post by eqvinox » Mon, Jan 06, 2025, 8:09 PM UTC

Unfortunately, nested functions are one of the few GCC extensions not implemented by clang, as such this really only works on GCC.

Re: C: Simple Defer, Ready to Use

#36

Post by bangaladore » Mon, Jan 06, 2025, 8:09 PM UTC

I'm a strong believer that if C had defer, many bugs would disappear. The number 1 issue I find myself having when switching from C++ to C is missing RAII (Main C++ way of implementing defer).

Re: C: Simple Defer, Ready to Use

#37

Post by eqvinox » Mon, Jan 06, 2025, 8:11 PM UTC

uecker wrote: post #32

accelbred wrote: post #31

Earlier quoted context omitted.

The macro from the article uses nested functions which on gcc are implemented with tramolines that need executable stack. https://thephd.dev/lambdas-nested-functions-block-expression...

The trampolines are not generated in this case.

To be fair you're not communicating very well — there are no trampolines being used here because the call site is directly in the same function, so no trampoline is needed with already being in the correct stack frame.

(And also on -O1 and higher the entire call is optimized out and the nested function inlined instead.)

Re: C: Simple Defer, Ready to Use

#38

Post by jagrsw » Mon, Jan 06, 2025, 8:14 PM UTC

Ages old (~2014 IIRC) defer implementation for gcc and for clang:

https://github.com/google/honggfuzz/blob/c549b4c31815e170d3b...

Re: C: Simple Defer, Ready to Use

#39

Post by joshmarinacci » Mon, Jan 06, 2025, 8:15 PM UTC

Unfortunately the first thing I see is a giant ad scroll down over the header blocking the entire viewport on my phone, so immediately hit the back button. Are all personal blogs automatically monetized now?

Re: C: Simple Defer, Ready to Use

#40

Post by [deleted] » Mon, Jan 06, 2025, 8:17 PM UTC

accelbred wrote: post #15

Unfortunately, this requires an executable stack, and only works on gcc, though an alternate implementation can work on clang. After a few attempts at defer, I ended up using a cleanup macro that just takes a function and a value to pass to it: https://github.com/aws-greengrass/aws-greengrass-lite/blob/8... Since the attribute or a function-like macro in the attribute position broke the c parsing in some tooling, I m…

[deleted]