The 29th International Obfuscated C Code Contest (IOCCC) 2025 Winners

aquir

The website itself is obfuscated, it’s not easy to find the C sources at all!

haunter

The GameBoy emulator's code also looks like the GameBoy. Slow clap this is insane, definitely my favorite entry. https://github.com/ioccc-src/winner/blob/master/2025/ncw1/pr... The author, Nick Craig-Wood, is the creator of rclone!

larodi

Tis a pity to not have LLMs compete, given level of obfuscation they be capable of.

rurban

So like at a film festival, 90% of the entries won a price, but unlike a film festival there's not a single best. Weird, like modern education.

yayitswei

In case anyone was wondering, the IOCCC specifically permits LLM use in their guidelines. "The IOCCC has a rich history of remarkable winning entries created by authors who skillfully employed various techniques (often their own tools) to develop their code."

s-macke

My favorite is the 366-byte C program emulator that can run Linux and Doom [0]. The VM implements an OISC - a One Instruction Set Computer [1]. [0] https://github.com/ioccc-src/winner/blob/master/2025/cable/p... [1] https://github.com/ioccc-src/winner/blob/master/2025/cable/R...

nsoonhui

I'm not sure this kind of competition is still meaningful, given that LLM can easily convert a program clearly written in any programming language to the most obfuscated C code, and can still easily verify it's correctness in an automated way. Do I miss anything?

TZubiri

I love the submissions of IOCCC generally, but the schedule and submission process looks like a mess, is that part of the joke? Or is it just because being consistent and designing a simple process is hard¡

ollybee

I with the Underhanded C Contest would come back, it was far more interesting to me. No disrespect intended to the Obfuscated C competitors.

msk-lywenn

OMG, my game boy game of life implementation is included in one of the winning entries!

roer

There's a Frieren [1] reference in there! https://www.ioccc.org/2025/yang2/index.html One of the main characters is called Fern, and she almost exclusively uses the common offensive magic of Zoltraak. [1] https://en.wikipedia.org/wiki/Frieren

Gathering6678

There's another contest called Underhanded C that I enjoyed a lot reading, but it has been inactive for a decade at this point...

locao

Back in 2000 I was being interviewed for my first internship, to join a team of C programmers. They showed me one of the winner entries of the prior years, asked me to review the code and left the room. About 5 minutes later they came back: – And? – I'm sorry I wasted your time. I just can't understand it. They burst into laughs and asked me to start the joining process. I wonder if people still make fun of interns. I still have a good laugh when I remember myself freaking out.

stiray

OOOOOH! IOCCC is back! All my love <3 <3 <3 to organizers, thank you for continuing the IOCCC context, please never go away again!

EGreg

Wait, I kind of don't get it. So Obfuscated C Code Contest works but Capture the Flag doesn't? Because of AI? https://twit.tv/posts/tech/ai-disrupts-capture-flag-what-mea...

LearnYouALisp

Some comments suggested the idea, have there been any IOCCC entries written in pre-64bit DEBUG.COM? (which could <read a file as input)