Why I am not getting OutOfBounds exception (like Java one) or any other error in C when I violate array size constraints?

Question

I am curious about below code in C

int main(){

        int arr[10];
        *(arr+120) = 5;
        int *px = arr;
        int i = 0;
        for(i = 0; *px != 5; px++){
          i++;
        }

        printf("%d", i);
}

This code produced output of 120. Our array is said to hold 10 items. How can I assign some value for index 120, run loop and get my value if there potentially should be some kind of error. Probably I am not getting some C language specifics. In java I would get OutOfBounds exception.... Please, help to clarify it. Thank you!

In C, it's up to you to do the checking for that sort of thing. The compiler isn't going to check for you. — AntonH, Jul 14 '14 at 16:19
C doesn't do array bounds checking. Further, C doesn't have exceptions. — Elliott Frisch, Jul 14 '14 at 16:20
you're allowed to shoot yourself in the foot in all sorts of fantastical way in C — Ben, Jul 14 '14 at 16:20

score 3 · Accepted Answer · answered Jul 14 '14 at 16:19

3

C does not check array bounds, and the code accessing out-of-array elements is undefined behaviour, which means that anything may happen - including the result you got.

answered Jul 14 '14 at 16:19

Wojtek Surowka

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oh, wow.. it is tricky. Thanks – Unfairnessrulestheworld Jul 14 '14 at 16:22

Why I am not getting OutOfBounds exception (like Java one) or any other error in C when I violate array size constraints?

1 Answers1