Re: Looping forever,can this be right?

["Burak Serdar" <bserdar at ieee dot org>]

It appears that the address of a[11] coincides with the variable i on
the stack, so when you execute a[11]=1, i is reset to 1, and it keeps
looping forever. That's why you see a[2] printed after a[11], because
a[11]=1 sets i to 1, and the for loop increments i to 2. When you set
a[11]=11, the loop continues by incrementing i to 12, and moves on
writing over to the rest of the stack.

On 3/11/06, Petur Thors <peturth@hi.is> wrote:
> Hi
> Please correct me if I'm totally lost here , but compiling this program
> (a.c)  with gcc -Wall -pedantic -o a a.c :
>
> #include <stdio.h>
> int main(int argc,char **argv)
> {
>     int i;
>     int a[10];
>     for(i = 0; i < 2000; i++) {
>         printf("a[%d] is %d\n",i,a[i]);
>         a[i] = 1;
>     }
>     return 0;
> }
>
>
> and running it i get :
>
> a[0] is 0
> a[1] is 0
> a[2] is -2146329632
> a[3] is 51
> a[4] is 4195584
> a[5] is 0
> a[6] is 4195312
> a[7] is 0
> a[8] is -4327808
> a[9] is 32767
> a[10] is 0
> a[11] is 11
> a[2] is 1
> a[3] is 1
> a[4] is 1
> a[5] is 1
> a[6] is 1
> a[7] is 1
> a[8] is 1
> a[9] is 1
> a[10] is 1
> a[11] is 11
> a[2] is 1
> a[3] is 1
> a[4] is 1
> a[5] is 1
> a[6] is 1
> a[7] is 1
> ....
> looping forever and ever........
>
> But when I change a[i] = 1 to a[i] = 11 (in the for loop) it segfaults
> at i = 1532.
>
> Please forgive me if I'm totally missing something obvious here but can
> this be correct ?
>
> gcc specs:
>
> Using built-in specs.
> Target: x86_64-redhat-linux
> Configured with: ../configure --prefix=/usr --mandir=/usr/share/man
> --infodir=/usr/share/info --enable-shared --enable-threads=posix
> --enable-checking=release --with-system-zlib --enable-__cxa_atexit
> --disable-libunwind-exceptions --enable-libgcj-multifile
> --enable-languages=c,c++,objc,java,f95,ada --enable-java-awt=gtk
> --with-java-home=/usr/lib/jvm/java-1.4.2-gcj-1.4.2.0/jre
> --host=x86_64-redhat-linux
> Thread model: posix
> gcc version 4.0.2 20051125 (Red Hat 4.0.2-8)
> Updated Fedora core 4
>
> Thanks in advance and best regards
> Petur
>
>
>