The Shortest Crashing C Program

This reminds me of "A Whirlwind Tutorial on Creating Really Teensy ELF Executables for Linux" [1]. The author tries to create the smallest possible elf executable possible. You would think it'd be easy... :) go read it. Very cool!<p>[1] <a href="http://www.muppetlabs.com/~breadbox/software/tiny/teensy.html" rel="nofollow">http://www.muppetlabs.com/~breadbox/software/tiny/teensy.htm...</a>

It depends on the definition. You can do better than this if you define a valid C program as anything that passes though the C compiler and generates an executable. Behold the zero length program:<p>$ touch a.c<p>$ gcc -c a.c<p>$ ld a.o<p>ld: warning: cannot find entry symbol _start; defaulting to 0000000000400078<p>$ ./a.out<p>Segmentation fault

The explanation is not quite correct - execution starts at &#38;main rather than the address given by the value of main. On VC++, at least - well, on my PC anyway - the process halts because the data segment doesn't have the execute bit set. It isn't trying to run code at address 0.<p>(If execution of bytes in the data segment were possible, which I'm sure it used to be, then you'd still likely get a crash, but it's not guaranteed. (uint32_t)0 is a valid sequence of instructions - it's ADD BYTE PTR [EAX],AL - and so if EAX contained a valid value then it would execute without a problem. Then, if the following byte were 0xC3 (RET) then the program would execute. OK, so that's all rather unlikely, but you have to bear these things in mind. So I think 0xCC (INT 3) would be a better choice.)

Seems to work really well: It even crashed the website.

Who says it will crash? Could run very nicely, printing a list of prime numbers, or write poetry, or anything else that undefined behaviour encompasses.

It seems to be down, google cache: <a href="http://webcache.googleusercontent.com/search?q=cache:4FhUcns72Z4J:llbit.se/%3Fp%3D1744+&#38;cd=1&#38;hl=es-419&#38;ct=clnk&#38;gl=ar" rel="nofollow">http://webcache.googleusercontent.com/search?q=cache:4FhUcns...</a>

The first IOCCC winner declared main as a short[] of VAX machine code: <a href="http://www.ioccc.org/1984/mullender.c" rel="nofollow">http://www.ioccc.org/1984/mullender.c</a><p>You could probably do the same thing in x86 and it'd work on a modern compiler.

&#62; Also, global variables in C are initialized to zero implicitly, so this is equivalent:<p>EDIT: <i>this</i> is wrong, see below.<p>That's wrong. 'static' variables are initialized to zero. Non-static variables are un-initialized, so they have a "random" value.<p>See:<p>$ valgrind ./a.out<p>==5118== Memcheck, a memory error detector<p>==5118== Copyright (C) 2002-2012, and GNU GPL'd, by Julian Seward et al.<p>==5118== Using Valgrind-3.8.1 and LibVEX; rerun with -h for copyright info<p>==5118== Command: ./a.out<p>==5118==<p>==5118==<p>==5118== Process terminating with default action of signal 11 (SIGSEGV)<p>==5118== Bad permissions for mapped region at address 0x600864<p>==5118== at 0x600864: ??? (in /home/def/a.out)<p>==5118== by 0x4E54A14: (below main) (in /usr/lib/libc-2.17.so)

You can go even shorter if you cheat:<p><pre><code> $ cat short.c M $ gcc -DM='main;' short.c -o short $ ./short Segmentation fault</code></pre>

The Shortest Crashing Wordpress Site

The site seems down, "Error establishing a database connection"

I'm not convinced this is a C89 program. It is only an "accident" that the linker doesn't know about types.<p>I find it hard to believe that the C89 spec states that an integer called "main" is to be considered the main function, and suspect this is undefined behaviour (though I've not checked).

How about:<p><pre><code> main(){*(int*)0=0;} </code></pre> or:<p><pre><code> main(){*""=0;} </code></pre> or:<p><pre><code> main(){main();}</code></pre>

Seems appropriate that the default C program, as it were, segfaults.

"address 0, which is not an address that we have access to"<p>if I'm not mistaken, there are platforms like TI C600 dsps for which 0 is the start of the usable address space

Interesting. We tried to do the same for Haskell. The shortest we could come up with:<p>import Unsafe.Coerce;main=unsafeCoerce()1

With visual studio V6.0 (AFAIR), I made a short program that crashed the compiler:<p>int a;::a::b();

It's also the shortest C program that you can link at all.

"The shortest crashing C89 program" to be more precise. :)

And interesting question, what would be the shortest not crashing C program?<p>main(){}<p>??

reminds me of the recent fad of TAS (tool assisted speed run) videos of "fastest crash" of video games.

Shortest crashing website: Error establishing a database connection

for those who see the server crashing: The program is in C89<p>main;