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Similarly, comparing pointers using the relational operators <, <=, >=, and > gives the positions of the pointers relative to each other. Subtracting or comparing pointers that do not refer to the same array can result in erroneous behavior.
Comparing pointers using the equality operators == and != has well-defined semantics regardless of whether or not either of the pointers is null, points into the same object, one past the last element of an array object, or function.
It is acceptable to subtract or compare two member pointers within a single struct object, suitably cast, because any object can be treated as an array of unsigned char. However, when doing so remember to account for the effects of alignment and padding on the structure.
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The first incorrect assumption is that the nums and strings arrays are necessarily contiguous in memory. The second is that free_bytes is the number of bytes available. The subtraction returns the number of elements between next_num_ptr and strings.
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