I think we should be focusing on this example for a minute.

So let's say we have a Harvard Architecture microcontroller, with code memory (non-volatile) separate from data memory (volatile), and let's say it has 65 kilobytes of SRAM.

If address 0 is accessible in the SRAM, then there's three viable strategies:

(1) Make nullptr == 0xffff

(2) Make nullptr == 0xfffe

(3) Make nullptr == 0x0000, but before any pointer is dereferenced, subtract 1 from it.

With strategy No. 3, a pointer would have the bit pattern 0x0001 in order to access address 0.

Next question then is: If you want to identify the last byte as a range, i.e. [begin,end) , then will the end pointer be the same as the nullptr? If this must be avoided then it seems like 1 byte in the SRAM must be inaccessible from the C++ programming language. Unless it were to be stipulated that the end pointer might be equal to a null pointer.

And then what happens if we introduce badptr? Will badptr be given the bit pattern 0xFFFF? Subtracting 1 from it would give 0xFFFE -- but maybe that subtraction should never take place if the operand is 0xFFFF.