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The '''International Obfuscated C Code Contest''' (abbreviated '''IOCCC''') is a [[computer programming]] contest for [[Source code|code]] written in [[C (programming language)|C]] that is the most creatively [[obfuscated code|obfuscated]]. Heldand held semi-annually, it(when possible). It is described as "celebrating [C's] syntactical opaqueness".<ref>{{cite web |url=http://pcworld.co.nz/pcworld/pcw.nsf/how-to/beyond-the-command-line |access-date=2013-04-07 |title=Beyond the command line |work= [[PC World]] New Zealand| last=Palmer| first= Geoff| date=November 1, 2004| publisher= Fairfax Media, Fairfax New Zealand Limited |url-status=dead |archive-url= https://web.archive.org/web/20130210081342/http://pcworld.co.nz/pcworld/pcw.nsf/how-to/beyond-the-command-line |archive-date=February 10, 2013 }}</ref> The winning code for the 28th contest, held in 2024/25, was announced by live stream 2 Aug 2025.<ref>{{cite web |url= https://www.ioccc.org/years.html |title=Previous IOCCC Winners with spoilers |publisher= International Obfuscated C Code Contest | website= IOCCC.org |access-date=2023-05-01}}</ref> Previous contests were held in the years 1984–1996, 1998, 2000, 2001, 2004–2006, 2011–2015, 2018–2020, and 2024.
Entries are evaluated anonymously by the current sitting judges (currently, Leonid A. Broukhis & Landon Curt Noll). The judging process is documented in the competition guidelines<ref name= guidelines>{{cite web |url=https://www.ioccc.org/next/guidelines.txt html#judging-process|title=Current GuidelinesJudging Process|format=plain textHTML |publisher= International Obfuscated C Code Contest | website= IOCCC.org |access-date=20232025-0508-0127}}</ref> and consists of elimination rounds. By tradition, no information is given about the total number of entries for each competition. Winning entries are awarded with a category, such as "Worst Abuse of the [[C preprocessor]]" or "Most Erratic Behavior", and then announced on the official IOCCC website. The contest states that being announced on the IOCCC website is the reward for winning (plus bragging rights).
==History==
The IOCCC was started by [[Landon Curt Noll]] and Larry Bassel in 1984 while employed at National Semiconductor's Genix porting group. The idea for the contest came after they compared notes with each other about some poorly written code that they had to fix, notably the [[Bourne shell]], which used macros to emulate [[ALGOL 68]] syntax, and a buggy version of [[finger (Unix)|finger]] for BSD.<ref>{{cite web |url=https://www.ioccc.org/faq.html#ioccc_start |title=TheHow FAQit started|publisher= International Obfuscated C Code Contest | website= IOCCC.org| date= |access-date=20232025-0508-0127}}</ref> The contest itself was the topic of a quiz question in the 1993 Computer Bowl.<ref>{{cite news| url= http://nl.newsbank.com/nl-search/we/Archives?p_product=SJ&s_site=mercurynews&p_multi=SJ&p_theme=realcities&p_action=search&p_maxdocs=200&p_topdoc=1&p_text_direct-0=0EB71B1E74EA9019&p_field_direct-0=document_id&p_perpage=10&p_sort=YMD_date:D&s_trackval=GooglePM |title= Top Execs Fail To Compute Correctly| first= | last= | work= [[San Jose Mercury News]]| place= California| date= May 15, 1993| page= 1A| via= [[Newsbank]]| url-access= subscription| url-status= dead| archiveurl= https://web.archive.org/web/20140808041942/http://nl.newsbank.com/nl-search/we/Archives?p_product=SJ&s_site=mercurynews&p_multi=SJ&p_theme=realcities&p_action=search&p_maxdocs=200&p_topdoc=1&p_text_direct-0=0EB71B1E74EA9019&p_field_direct-0=document_id&p_perpage=10&p_sort=YMD_date:D&s_trackval=GooglePM| archivedate= 2014-08-08| access-date= 2025-08-08}}</ref> After a hiatus of five years starting in 2006, the contest returned in 2011.<ref name=SJMerc11>{{cite web| url= https://www.pcworld.com/article/478306/obfuscated_code_contest_returns.html |title=Obfuscated Code Contest Returns |magazine=[[PC World]]|date=November 15, 2011|last=Jackson|first=Joab| publisher= |access-date=2023-05-01}}</ref>
Compared with other programming contests, the IOCCC is described as "not all that serious" by [[Michael Swaine (technical author)|Michael Swaine]], editor of ''[[Dr. Dobb's Journal]]''.<ref>{{cite journal |url=https://www.drdobbsjacobfilipp.com/architecture-and-designDrDobbs/there-must-be-contestarticles/207404123 DDJ/2008/0806/080501ms01/080501ms01.html|title=There Must be Contest |first=Michael |last=Swaine |author-link=Michael Swaine (technical author) |journal=[[Dr. Dobb's Journal]]|date=May 1, 2008 |access-date=20232025-0508-0127}}</ref>. Thought many IOCCC contestants may beg to differ.
==Rules==
EachThe year,Rules<ref thename=rules>{{cite web|url=https://www.ioccc.org/next/rules.html|title=Rules|publisher= International Obfuscated C Code Contest | website= IOCCC.org }}</ref> vary from year to year and are posted with a set of Guidelines<ref name=guidelines>{{cite web|url=https://www.ioccc.org/next/guidelines.html|title=Guidelines|publisher= International Obfuscated C Code Contest | website= IOCCC.org }}</ref> that attempt to convey additional enlightenment about the contestRules. They are published on the IOCCC website. All In addition all material isincluding winning entries are published under [[Creative Commons license]] [[Share-alike|BY-SA]] 34.0 UnportedInternational.<ref>{{cite web| url= https://www.ioccc.org/ license.html|title= IOCCC home page| at= FooterLicense Employed|publisher= International Obfuscated C Code Contest | website= IOCCC.org| date= | access-date= }} Also in each hint.txt file.</ref> Rules vary from year to year and are posted with a set of guidelines that attempt to convey the spirit of the rules.
{{quotebox|text=Hacking the contest rules is a tradition.| author= —Landon Curt Noll, 2011<ref name=SJMerc11 />}}
The rulesRules are often deliberately written with [[loophole]]s that contestants are encouraged to find and abuse.<ref name=guidelines /> Entries that take advantage of loopholes can cause the rules for the following year's contest to be adjusted.<ref name=guidelines />
The most significant of the Rules is Rule 2a & 2b (originally Rule 1), gross & net source size limits. During the life time of the contest, Rule 2 has evolved<ref>{{cite web|url=https://www.ioccc.org/faq.html#size_rule_history|title=Rule 2 Eras|publisher=International Obfuscated C Code Contest|website=IOCCC.org}}</ref> to accommodate subtle increases in source size limits. The 1984 contest started with a maximum source size of 512 bytes, which increased a few more times to 1536 bytes in 1991. In 1992, Rule 2 was split to distinguish between maximum overall size and maximum size ignoring white space and semicolons given certain conditions. In the early days, in order to make best use of space allowed, white space was stripped, often resulting in a compact blob of text, making it hard to read by humans, but served little purpose once passed through a C "pretty print" utility, which the judges did as part of their process. In 1992 the judges believed that form of obfuscation had played out and they wanted to encourage people to explore other ways of formatting the code, such as an ASCII image themed after the entry, or simply more traditionally indented C source. Around 2012/2013 the iocccsize(1)<ref>{{cite web|url=https://github.com/SirWumpus/iocccsize#history|title=iocccsize|publisher=Anthony C Howe|website=GitHub.com}}</ref> tool was adopted by the contest and tweaked to aid both contestants and judges apply the Rule 2b counting algorithm.
==Obfuscations employed==
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