3 ms·

I don't have all ca 200 UBs in my head (see https://gist.github.com/Earnestly/7c903f481ff9d29a3dd1 https://gist.github.com/Earnestly/7c903f481ff9d29a3dd1), but

I don't have all ca 200 UBs in my head (see https://gist.github.com/Earnestly/7c903f481ff9d29a3dd1 https://gist.github.com/Earnestly/7c903f481ff9d29a3dd1), but I'm pretty sure all types of illegal memory accesses count as UB. For instance from skimming the list: - An object is referred to outside of its lifetime (6.2.4). - The value of a pointer to an object whose lifetime has ended is used (6.2.4). - An array subscript is out of range, even if an object is apparently accessible with the given subscript (as in the lvalue expression a[1][7] given the declaration int a[4][5]) (6.5.6).

planede 3y ago
Technically the array subscript example is UB even before the dereference. a[1][7] is equivalent to `*(a[1] + 7)` and a[1] + 7 itself is UB. (6.5.7) Additive operators > If the pointer operand and the result do not point to elements of the same array object or one past the last element of the array object, the behavior is undefined. Interestingly a[1][5] is also UB, but for the dereferencing a past-the-end pointer, not for the arithmetic.
gpderetta 3y ago
Yes, that's exactly what I meant. Also, dereferencing a pointer with the wrong dynamic type. > all ca 200 UBs in my head Technically there is no enumerated set of all possible UB. Anything not explicitly defined in the standard is UB. /extremely-pedantic
- tialaramex 3y ago
  Effort to try to write an appendix listing all the UB and IFNDR is an ambition of WG21 but there's no specific timeline. It's a bit like that "Migrate off obsolete DB server" card that's been sat in your team's (well most teams) backlog for a couple of years. Everybody agrees it should be done... But like not this sprint. My assessment is that at their current rate WG21 is adding new UB to the language slightly faster than it's being documented for the appendix, so this won't actually finish.

planede 3y ago

Technically the array subscript example is UB even before the dereference. a[1][7] is equivalent to `*(a[1] + 7)` and a[1] + 7 itself is UB. (6.5.7) Additive operators > If the pointer operand and the result do not point to elements of the same array object or one past the last element of the array object, the behavior is undefined. Interestingly a[1][5] is also UB, but for the dereferencing a past-the-end pointer, not for the arithmetic.

gpderetta 3y ago

Yes, that's exactly what I meant. Also, dereferencing a pointer with the wrong dynamic type. > all ca 200 UBs in my head Technically there is no enumerated set of all possible UB. Anything not explicitly defined in the standard is UB. /extremely-pedantic

tialaramex 3y ago
Effort to try to write an appendix listing all the UB and IFNDR is an ambition of WG21 but there's no specific timeline. It's a bit like that "Migrate off obsolete DB server" card that's been sat in your team's (well most teams) backlog for a couple of years. Everybody agrees it should be done... But like not this sprint. My assessment is that at their current rate WG21 is adding new UB to the language slightly faster than it's being documented for the appendix, so this won't actually finish.