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

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

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!

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

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.

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."

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...

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?

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¡

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

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

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

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

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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.

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OOOOOH! IOCCC is back!

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

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...

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

Is it zero-indexed, or are they really behind in choosing winners, or am I loosing my mind... Isn't it 2026 not 2025??