4 ms·

If you know that the strings are stored in the same table, couldn't you subtract from each pointer a pointer to the beginning of the table and hash the resultin

• caf 10y ago
  Yes.
• svens_ 10y ago
  That's probably true, however there's a small catch. Looking at the standard (no difference between C99/C11), chapter 6.5.6 ("additive operators"), point 9 defines the behavior of pointer subtraction: When two pointers are subtracted, both shall point to elements of the same array object, or one past the last element of the array object; the result is the difference of the subscripts of the two array elements. However reading further: The size of the result is implementation-defined, and its type (a signed integer type) is ptrdiff_t defined in the <stddef.h> header. If the result is not representable in an object of that type, the behavior is undefined. Unlike the (u)intptr_t types, ptrdiff_t is not optional AFAIK. The way I understand it, you could still invoke UB if the implementation uses a very silly type for ptrdiff_t, though I didn't do further research on it. Still, using pointer difference makes this a lot safer and more portable. Especially on platforms with unusual memory models, where a pointer might not be just a single integer (e.g. segmented memory on x86). Also the operation is Theta(1), so it doesn't impact performance much.
• deleted 10y ago
  [deleted]