The International Obfuscated C Code Contest (abbreviated IOCCC) is a computer programming contest for code written in C that is the most creatively obfuscated and held annually (when possible). It is described as "celebrating C's syntactical opaqueness". The winning code for the 28th contest, held in 2024/25, was announced by live stream 2 Aug 2025 in addition video segments for each of the 23 winners.

Entries are evaluated anonymously by the current sitting judges, Leonid A. Broukhis & Landon Curt Noll. The judging process is documented in the competition FAQ 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).

Previous contests were held in the years 1984–1996, 1998, 2000, 2001, 2004–2006, 2011–2015, 2018–2020, and 2024.

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 for BSD. The contest itself was the topic of a quiz question in the 1993 Computer Bowl. After a hiatus of five years starting in 2006, the contest returned in 2011.

Compared with other programming contests, the IOCCC is described as "not all that serious" by Michael Swaine, editor of Dr. Dobb's Journal.

In Don Libes' book says:

<blockquote>...they will undoubtedly force you to expand your own mind when you study them. And admittedly, some are just downright insane and only good for laughing at and making fun of.</blockquote>

Rules

The Rules vary from year to year and are posted with a set of Guidelines that attempt to convey additional enlightenment about the Rules. They are published on the IOCCC website. In addition all material including winning entries are published under Creative Commons license BY-SA 4.0 International.

" */ return k- -1+ /*\' '-`*/

( -/*}/ */0x01 ); {;{

; /*^w^*/ ;}

</syntaxhighlight>

If the program is run using its own source as the input, the result is:

<syntaxhighlight lang="c">

$ ./akari akari.c

int

  • w,m,_namori=('n');
  1. include<stdio.h>/*;hrd"% dnd4%"*/

/**/int(y),u,r[128*2/*{y}icuhya*rr*rya=

  • /];void/**/i(){putchar(u);}int/**/main(/*

"(n"l)?M5{YlcpvdluvKct[j skao(tve"t"oYRYR"

  • /int(w),char**n){for(m =256;--m;r[m]/*

"<*]y+u>r>u+y-u-r+i+" ) ;>m.a.i+n>()/q*/

=25<(31&( m -1))||64-( m &192)||2>w?m:(2+

m/*"*,/U// R/)/U * & /Y/0/U/=P &=/"*/)\

&16?m-13 : 13+ m) ;u=+10 ;for(;(m=/*

  • >/()/{ p u t-s +(yy*+ n1>7?/:*/

getchar ())+1 ;i() ){if(10/*

"wNMR;{ I/=/" )/{*/==u*1

)i(); if(m-10){

u=/*> *./<)[;*/8*

4;i(); }u=r[ m];}return(

  • *n/*{i ;w; }_}

( -*/ *00 ) ; }

$ ./akari akari.c > ./akari.small

$ ./akari ./akari.small

wm_aoi(n)

/*ity,,[2*/{}char*y=

(")M{lpduKtjsa(v""YY"

"*yuruyuri") ;main(/*

/",U/ R)U* Y0U= ="/\

  • /){puts (y+ 17/*

"NR{I=" ){/=*

=* */);/*

  • /{ ;;

$

$ ./akari ./akari.small > ./akari.smaller

$ ./akari ./akari.smaller

main

(){puts("Y"

"U RU YU "\

"RI" )/*

  • / ;}

$

</syntaxhighlight>

See also

  • Obfuscated Perl Contest
  • Underhanded C Contest
  • Esoteric programming language
  • Code golf

Notes

References

  • Mmm… Obfuscated Shell Donuts, Sven Gregori
  • LaurieWired - A Competition for Unreadable Code?
  • LaurieWired - This C code should be ILLEGAL. It's also fantastic.
  • The World of Obfuscated, Esoteric, Artistic Programming" by Yusuke Endoh (IOCCC winner x20)
  • Cracking Complexity: ChatGPT's Exploration of Enigmatic C Code from the IOCCC
  • Expert C Programming, Peter van der Linden, ch. 8, p. 225 "Some Light Relief" ISBN 0131774298
  • IOCCC 2024 Sets Record with 23 Winners After 4-Year Break, Features AI Chatbot and Moon Phase Calculator