Why do private member variables behaved like protected in the same module when creating deriving class?

[Steven Schveighoffer]

On 11/1/18 4:15 PM, Paul Backus wrote:
> On Thursday, 1 November 2018 at 19:26:05 UTC, Steven Schveighoffer wrote:
>>
>> My testing looks like it's the same:
>>
>> #include <stdio.h>
>> int main()
>> {
>>     int arr[5];
>>     int *ptr = arr + 1; // point at second element so we can do 
>> negative indexing legally
>>     int idx1 = 0;
>>     ptr[--idx1] = 5;
>>     printf("%d\n", arr[0]); // 5
>>     size_t idx2 = 0;
>>     ptr[--idx2] = 6;
>>     printf("%d\n", arr[0]); // 6
>>     return 0;
>> }
>>
> 
> `ptr[--idx2]` is undefined behavior (out-of-bounds array access), so the 
> fact that it works that way is just a coincidence.

Either way, I don't see it causing a segfault -- the purported benefit.

But maybe on Patrick's actual arch it did. In any case, undefined 
behavior is bad whether you do it with an int or size_t :)

-Steve