The International Obfuscated C Code Contest

The 27th IOCCC

2020 marked the “The Twenty Seventh International Obfuscated C Code Contest”

Copyright © 2020, Landon Curt Noll, Simon Cooper, and Leonid A. Broukhis. All Rights Reserved. Permission for personal, educational or non-profit use is granted provided this copyright and notice are included in its entirety and remains unaltered. All other uses must receive prior permission from the contest judges.

Standard IOCCC stuff

The primary IOCCC web site can be found at,

Use make to compile entries. It is possible that on non-Un*x / non-Linux systems the makefile needs to be changed. See the Makefile for details.

Look at the source and try to figure out what the programs do, and run them with various inputs. If you want to, look at the hints files for spoilers - this year we included most of the information included by the submitter.

Read over the makefile for compile/build issues. Your system may require certain changes (add or remove a library, add or remove a #define).

Some C compilers are not quite as good as they should be. If yours is lacking, you may need to compile using clang or gcc instead of your local compiler.

Remarks on some of the winners

This year’s Best of Show (carlini) is such a novel way of obfuscation that it would be worth of a special mention in the (future) Best of IOCCC list!

For some reason, this year’s set of winners contains three nostalgic games, Asteroids (tsoj), Minesweeper (endoh1), and Snake (ferguson1).

An entry (kurdyukov1) pays homage to a previous winner (2015/hou).

…We’ll stop spouting spoilers now. Have fun exploring all the entries!

Remarks on some of submissions that did not win

As a rule, we try to compile the entries on a variety of platforms. Quite a few entries this year could not be built or executed on some of them due to reliance on library internals or the system runtime.

A few entries were violating the “2053 significant bytes” rule. If an entry could not be brought to compliance within a few seconds of looking at the source, it was disqualified.

One entry tried to get around the size limit by putting the code into makefile variables and using -D. This is already called out as discouraged technique in the guidelines, but it is worth a reminder.

Several promising entries attempted to make use of the syscall function using literal syscall numbers. This is utterly non-portable.

A note to the authors: when submitting multiple entries, don’t let us easily correlate them by coding style or documentation content, and definitely don’t submit nearly identical versions of your program separately. As we try to judge the entries anonymously, the similarities will cause such entries to compete against one another, making each less likely to win.

We hope the authors of non-winning entries will refine their entries and perhaps re-submit them for the next IOCCC.

Final Comments

One more thing that feels dated is digraphs and trigraphs.

Please feel free to send us comments and suggestions about the competition, this README or anything else that you would like to see in future contests.

If you use, distribute or publish these entries in some way, please drop us a line. We enjoy seeing who, where and how the contest is used.

If you have problems with any of the entries, AND YOU HAVE A FIX, please send us the fix (patch file or the entire changed file).

For the latest information on how to contact the IOCCC Judges please visit

For news of the next contest watch:

Creative Commons License

© Copyright 1984-2020, Leo Broukhis, Simon Cooper, Landon Curt Noll - All rights reserved
This work is licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported License.