how dose this c program work?

Edvis

this is code:

#define q(k) main(){return!puts(#k"\nq("#k")");}
q(#define q(k) main(){return!puts(#k"\nq("#k")");})

than :

tangchaolei@tangchaolei-laptop:~/cx$ gcc h.c -o h
tangchaolei@tangchaolei-laptop:~/cx$ ./h
#define q(k) main(){return!puts(#k"\nq("#k")");}
q(#define q(k) main(){return!puts(#k"\nq("#k")");})

so , this program will print all the code .
but ,how dose it work ?
any ideal?

epegasus

把源程序的代码中的字符串保存在程序里,然后打印出来.
从另一方面考虑就是源代码中如果一个字符对编译器来说提供的信息量可以大于这个字符本身存储的信息量,那么能做到程序打印自身.

[ 本帖最后由 epegasus 于 2009-9-10 20:31 编辑 ]

huangwei0413

原帖由 Edvis 于 2009-9-10 20:07 发表
this is code:

#define q(k) main(){return!puts(#k"\nq("#k")");}
q(#define q(k) main(){return!puts(#k"\nq("#k")");})

than :

tangchaolei@tangchaolei-laptop:~/cx$ gcc h.c -o h
tangchaolei@ ...

It is that!

jeasun

#define q(k)main(){return!puts(#k"\nq("#k")");}

q(#define q(k)main(){return!puts(#k"\nq("#k")");})



把main中的#k用k的字符串代替（注意轉義字符）

main(){return!puts(#k"\nq("#k")");}

/* 下面的參數k是從q(#define q(k)main(){return!puts(#k"\nq("#k")");})

中提取出來的 */

/* k == #define q(k)main(){return!puts(#k"\nq("#k")");} */

預處理后

main(){return!puts("#define q(k)main(){return!puts(#k\"\\nq(\"#k\")\");}"\"\\nq(\""#defineq(k)main(){return!puts(#k\"\\nq(\"#k\")\");}"\")\");}


下面的工作就是打印出字符串了

Edvis

thank you very much ！~