Dereferencing one past the end pointer to array type

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This is CWG 232. That issue might seem like it’s mainly about dereferencing a null pointer but it’s fundamentally about what it means to simply dereference something that doesn’t point to an object. There is no explicit language rule about this case.

One of the examples in the issue is:

Similarly, dereferencing a pointer to the end of an array should be allowed as long as the value is not used:

char a[10];
char *b = &a[10];   // equivalent to "char *b = &*(a+10);"

Both cases come up often enough in real code that they should be allowed.

This is basically the same thing as OP (the a[10] part of the above expression), except using char instead of an array type.

Common wisdom is that it’s undefined behavior to dereference a one-past-the-end pointer. However, does this hold true for pointers to array types?

There is no difference in the rules based on what kind of pointer it is. my_past_end is a past-the-end pointer, so whether it’s UB to dereference it or not is not a function of the fact that it points to an array as opposed to any other kind of type.

While the type of is_this_valid an int* which gets initialized from a int(&)[3] (array-to-pointer decay), and thus nothing here actually reads from memory – that is immaterial to the way the language rules work. my_past_end is a pointer whose value is past the end of an object, and that’s the only thing that matters.

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