When checking for integer overflow, you may often write tests like p + i < p.
This works fine if p and i are unsigned integers, since any overflow in the
addition will cause the value to simply "wrap around." However, using this
pattern when p is a pointer is problematic because pointer overflow has
undefined behavior according to the C and C++ standards. If the addition
overflows and has an undefined result, the comparison will likewise be
undefined; it may produce an unintended result, or may be deleted entirely
by an optimizing compiler.
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