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In the standard's specification for pointer arithmetic ([expr.add]/4.2, we have:
Otherwise, if
Ppoints to an array element i of an array objectxwith n elements ([dcl.array]), the expressionsP + JandJ + P(whereJhas the value j) point to the (possibly-hypothetical) array element i + j ofxif 0 ≤ i + j ≤ n and the expressionP - Jpoints to the (possibly-hypothetical) array element i − j ofxif 0 ≤ i − j ≤ n.
What does "possibly-hypothetical" mean here? The passage already constrains the resulting pointer to be in range of the array. Well, including the one-past-the-end slot. Is that what it's referring to?
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Pointer arithmetic provides the programmer with a single way of dealing with different types: adding and subtracting the number of elements required instead of the actual offset in bytes.
Pointer Arithmetic in C++: These are addition and subtraction operations. A pointer arithmetic in C++ may be incremented or decremented. It means that we can add or subtract integer value to and from the pointer. Similarly, a pointer arithmetic can be subtracted( or added) from another.
Yes, it's the one-past-the-end "element".
[basic.compound]/3:[..] For purposes of pointer arithmetic ([expr.add]) and comparison ([expr.rel], [expr.eq]), a pointer past the end of the last element of an arrayxof n elements is considered to be equivalent to a pointer to a hypothetical array element n ofxand an object of typeTthat is not an array element is considered to belong to an array with one element of typeT. [..]
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