Array boundary in C

Question

Previously when manipulating an array, I can go over the array bounds and I know that C is lenient. Now when I access a value that out of those boundaries, I get an error [-Warray-bounds] and it prevents me from diving into memory. Code:

#include <stdio.h>
int main(void)
{
    int arr[] = {1,2,3,4,5}; 
    printf("arr [0] is %d
", arr[0]); 
    printf("arr[10] is %d
", arr[10]);     
}

errors:

address.c:12:31: warning: array index 10 is past the end of the array (which contains 5 elements) [-Warray-bounds]
    printf("arr[10] is %d
", arr[10]);

Is that something new in a compiler, and if yes, how can I disable or enable it?

Answer 1

i can go over array bound

You "can" in the sense that it doesn't affect the well-formedness of the program and thus won't necessitate the compiler to issue a diagnostic message. Despite not being required to, if a compiler is able to detect the bug, then it is allowed to warn the programmer.

However if you do this, then the behaviour of the program will be undefined. That means that nothing about the behaviour of the program is guaranteed by the language. Undefined behaviour is detrimental to the usefulness of the program and its avoidance is extremely important.

As such: Do not access an array out of bounds! It's a bad thing to do.

Is that something new in a compiler

"New" is relative. At least version 4.7.1 of GCC is able to detect this, and it was released about 9 years ago. Clang 3.0.0 is likewise able to detect it and it was released about 10 years ago.

how can i disable or enable it?

Compilers generally provide options to enable and disable specific warnings. The warning message that you quoted states which warning option has enabled it.

[-Warray-bounds]

I recommend to not disable the warning, and to fix the bug when ever you see this warning.