Exceeding array bound in C — Why does this NOT crash?

Question

I have this piece of code, and it runs perfectly fine, and I don\'t why:

int main(){
   int len = 10;
   char arr[len];
   arr[150] = \'x\';
}

Answer 1

Under the C spec, accessing an element past the end of an array is undefined behaviour. Undefined behaviour means that the specification does not say what would happen -- therefore, anything could happen, in theory. The program might crash, or it might not, or it might crash hours later in a completely unrelated function, or it might wipe your harddrive (if you got unlucky and poked just the right bits into the right place).

Undefined behaviour is not easily predictable, and it should absolutely never be relied upon. Just because something appears to work does not make it right, if it invokes undefined behaviour.