International Obfuscated C Code Contest

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The International Obfuscated C Code Contest (abbreviated IOCCC) is a programming contest for the most creatively obfuscated C code, held annually since 1984 with the exception of 1997, 1999, 2002, 2003, and 2006.[1]

Entries are submitted online, and go through a number of rounds of being judged by a panel of judges. Entries are judged on how obfuscated they are, and how creatively. Entries that make it through the final round are awarded with a category, such as "Worst Abuse of the C preprocessor" or "Most Erratic Behavior", and are announced on the official IOCCC website. Entries that do not make it are deleted and forgotten; the contest states that being announced on the IOCCC website is the award for winning.



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.[2]


Each year, the rules of the contest are published on the IOCCC website. Rules vary from year to year, and are posted with a set of guidelines that attempt to convey the spirit of the rules.

The rules are often deliberately written with subtle loopholes that contestants are somewhat encouraged to find and abuse. This is a result of the contest being a "parody of the software development process". Entries that take advantage of some loophole in the rules (whether or not they pass the final round of judging) cause the rules for the following year's contest to be adjusted accordingly (although often other subtle loopholes are deliberately introduced in the process).

Obfuscations employed

Due to the nature of the contest, entries often employ strange or unusual tricks, such as using the C preprocessor to do things it was not designed to do, or avoiding commonly-used constructs in the C programming language in favor of much more obscure ways of achieving the same thing. For example, some quotes from 2004 winners include:

To keep things simple, I have avoided the C preprocessor and tricky statements such as "if", "for", "do", "while", "switch", and "goto".[3]
We still aren't sure whether or not this is a useful program, but it's the first atomic fission we've seen in the IOCCC.[4]
Why not use the program to hide another program in the program? It must have seemed reasonable at the time.[5]
The program implements an 11-bit ALU in the C preprocessor. [6]
I found that calculating prime numbers up to 1024 makes the program include itself over 6.8 million times.[6]

Some ways in which contributions are notable include:

  • The appearance of the source code, formatted to resemble images, text, etc., after the manner of ASCII art.
  • Preprocessor redefinitions to make code harder to read.
  • Self-modifying code.
  • Worst abuse of the rules. In several years, an entry was submitted that was so patently absurd that it required a new definition of some of the rules for the next year.  This is regarded as a high honor. An example is the world's shortest self-reproducing program. The entry was a program zero bytes in length that if run printed zero bytes to the screen (simply an empty file).[7]

In the effort to take obfuscation to its extremes, contestants have produced programs which skirt around the edges of C standards, or result in constructs which trigger rarely used code path combinations in compilers. As a result, several of the past entries may not compile directly in a modern compiler, and some may even cause crashes.


Within the code size limit of only a few kilobytes, contestants have managed to do impressively complicated things — a 2004 winner turned out an operating system [8].

Below is a 1988 entry which calculates pi by looking at its own area: [9]

#define _ -F<00||--F-OO--;
int F=00,OO=00;main(){F_OO();printf("%1.3f\n",4.*-F/OO/OO);}F_OO()

(Note that the entry was written in K&R C; it doesn't work correctly in ANSI C without some change[10].)

Another good example is the following cleverly-written flight simulator, the winner of the IOCCC in 1998[11] as shown below:

#include                                     <math.h>
#include                                   <sys/time.h>
#include                                   <X11/Xlib.h>
#include                                  <X11/keysym.h>
                                          double L ,o ,P
                                         s[999],E,h= 8,I,
                                        1E3,r,t, u,v ,W,S=
                                        a,B,A=32.2,c, F,H;
                                        int N,q, C, y,p,U;
                                       Window z; char f[52]
                                    ; GC k; main(){ Display*e=
 XOpenDisplay( 0); z=RootWindow(e,0); for (XSetForeground(e,k=XCreateGC (e,z,0,0),BlackPixel(e,0))
; scanf("%lf%lf%lf",y +n,w+y, y+s)+1; y ++); XSelectInput(e,z= XCreateSimpleWindow(e,z,0,0,400,400,
0,0,WhitePixel(e,0) ),KeyPressMask); for(XMapWindow(e,z); ; T=sin(O)){ struct timeval G={ 0,dt*1e6}
; K= cos(j); N=1e4; M+= H*_; Z=D*K; F+=_*P; r=E*K; W=cos( O); m=K*W; H=K*T; O+=D*_*F/ K+d/K*E*_; B=
sin(j); a=B*T*D-E*W; XClearWindow(e,z); t=T*E+ D*B*W; j+=d*_*D-_*F*E; P=W*E*B-T*D; for (o+=(I=D*W+E
*T*B,E*d/K *B+v+B/K*F*D)*_; p<y; ){ T=p[s]+i; E=c-p[w]; D=n[p]-L; K=D*m-B*T-H*E; if(p [n]+w[ p]+p[s
]== 0|K <fabs(W=T*r-I*E +D*P) |fabs(D=t *D+Z *T-a *E)> K)N=1e4; else{ q=W/K *4E2+2e2; C= 2E2+4e2/ K
 *D; N-1E4&& XDrawLine(e ,z,k,N ,U,q,C); N=q; U=C; } ++p; } L+=_* (X*t +P*M+m*l); T=X*X+ l*l+M *M;
  XDrawString(e,z,k ,20,380,f,17); D=v/l*15; i+=(B *l-M*r -X*Z)*_; for(; XPending(e); u *=CS!=N){
                                   XEvent z; XNextEvent(e ,&z);
                                         N-LT? UP-N?& E:&
                                         J:& u: &h); --*(
                                         DN -N? N-DT ?N==
                                         RT?&u: & W:&h:&J
                                          ); } m=15*F/l;
                                          c+=(I=M/ l,l*H
                                          +I*M+a*X)*_; H
                                           )/S; K=F*M+(
                                           h* 1e4/l-(T+
                                           a=2.63 /l*d;
                                           X+=( d*l-T/S
                                            *(.19*E +a
                                            )-M* v +A*
                                            Z)*_; l +=
                                            K *_; W=d;
                                            "%5d  %3d"
                                            "%7d",p =l
                              O*57.3)%0550,(int)i); d+=T*(.45-14/l*
                             X-a*130-J* .14)*_/125e2+F*_*v; P=(T*(47
                             *I-m* 52+E*94 *D-t*.38+u*.21*E) /1e2+W*
                             179*v)/2312; select(p=0,0,0,0,&G); v-=(
                               )/107e2)*_; D=cos(o); E=sin(o); } }

This program needs this script on a Linux system to be compiled:

#! /bin/sh
cc banks.c -o banks -DIT=XK_Page_Up -DDT=XK_Page_Down \
	-DUP=XK_Up -DDN=XK_Down -DLT=XK_Left -DRT=XK_Right \
	-DCS=XK_Return -Ddt=0.02 -lm -lX11 -L/usr/X11R6/lib

See also

Notes and references

  1. International Obfuscated C Code Contest years page
  2. [1]
  3. IOCCC 2004 - Best Calculated Risk
  4. IOCCC 2004 - Best abuse of the Periodic table
  5. IOCCC 2004 - Best abuse of Indentation
  6. 6.0 6.1 IOCCC 2004 - Best Abuse of CPP
  7. "smr.hint" (plain text). IOCCC. 1994. Retrieved 2006-09-16. 
  8. "gavin.hint" (plain text). IOCCC. 2004. Retrieved 2007-03-13. 
  9. 5th International Obfuscated C Code Contest, 1988 - westley.c
  10. using gcc, compile with the following command line: gcc -traditional-cpp -o r r.c or gcc -E r.c | sed 's/- -/--/g' > r2.c ; gcc -o r2 r2.c (The source file is r.c)
  11. IOCCC Flight Simulator

External links

fr:International Obfuscated C Code Contest ja:IOCCC pl:International Obfuscated C Code Contest ru:International Obfuscated C Code Contest sr:IOCCC zh:国际C语言混乱代码大赛

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