2025 - The 29th IOCCC
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The International Obfuscated C Code Contest
2025 - The 29th IOCCC
← 2024<br>↑ top ↑<br>No next<br>Inventory
Twenty Ninth International Obfuscated C Code Contest
Where to start
See below for links to the 2025 winning IOCCC entries.
Check out the index.html web pages for each winning entry. They have<br>most of the information you need to compile and run the winning program.<br>Take a look at the winning source code and try to figure out how it works.<br>You might also want to check out the author’s remarks for even more details.
You may download all winning entries in the form<br>of a compressed tarball for this year’s contest.
General remarks on this contest
For IOCCC29 , the volume and quality of submissions were at near-historic heights.
IOCCC28 was speculated to have attracted a record number of submissions<br>due to the 4-year absence, allowing authors to refine their submissions,<br>resulting in a higher-than-usual submission quality.
IOCCC29 was the second consecutive contest after the 2020-2024 hiatus.<br>And yet, the number of submissions for IOCCC29 was similar to last<br>year’s contest, and the overall submission quality remained high for<br>this contest. So perhaps the increased submission volume, combined<br>with a higher-than-usual submission quality, is due to factors such<br>as improved website design, increased social media presence, authors<br>building on the ideas of past winning entries, and other factors?
Starting with the close of IOCCC28 , the procedures used for<br>closing the contest to new submissions, the judging process,<br>selecting the winning entries, preparing the update to the website,<br>and the process to create the live show on the<br>Our Favorite Universe<br>were carefully documented. And while this documentation required<br>additional time as well as more effort, the documentation process<br>resulted in overall improvements to how the IOCCC is run.
A few days after the presentation of the winning entries for IOCCC29 has been made<br>on the Our Favorite Universe<br>YouTube channel. The recording of the main show will be divided up into individual segments.<br>Then, each winning entry will be updated to include a link to a YouTube<br>segment under a new Award presentation near the top of the winning<br>entry’s index.html page.
Fun challenge info
We have added fun challenges to this year’s winning entries<br>competition, under the “Judges’ remarks ” section. After you figure<br>out what a given winning entry does, we encourage you to attempt the<br>fun challenge.
Some of these challenges are easier than others. In some cases, you’re<br>asked to create an alternative version of prog.c or a related file.<br>In some cases you are asked to produce an explanation about something.
If the fun challenge is still open (check the “A fun challenge ”<br>section for the given winning entry), consider submitting a<br>GitHub pull request as a contribution.
If the fun challenge is closed, but you think you have a better solution,<br>consider submitting a GitHub pull request as a contribution.<br>If the IOCCC Judges agree that you solution is better, we will consider it.
If you believe you have an even better (or improvement) to winning entry’s fun challenge,<br>please consider submitting a GitHub pull request,<br>for the IOCCC judges to consider.
Rules and Guidelines for this contest
The final versions of the IOCCC rules and guidelines that were in effect for this contest were:
2025 rules version 29.15 2025-12-02
2025 guidelines version 29.08 2025-12-02
The IOCCC rules and guidelines for IOCCC29 represented a substantial<br>rewrite over previous contests, thanks in part to a number of volunteers:<br>giving the IOCCC judges useful edits, text rewrites, consolidation,<br>as well as overall improved organization.
Looking forward to the next contest
We plan to open IOCCC30 towards the end of 2026 and have the contest run<br>for a similar amount of time, closing sometime towards the end of Q1 2027.
As we perform the actions needed to open IOCCC30 , we plan to internally<br>document the process as we did during the closing of IOCCC29 .
About two or three weeks after the IOCCC29 winning entries<br>have been posted, and we process some of the early<br>pull requests<br>against the 2025 directory tree, the<br>IOCCC Judges plan to go on an IOCCC vacation .
We had intended to go on an IOCCC vacation after releasing the winners of<br>IOCCC28 , but then the efforts to process bug fixes and enhancements<br>to the mkiocccentry repo<br>took so much time that by the time that repo was stable, it was time to<br>open IOCCC29 . Therefore, this time,...