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> The whole "prevent double free" claim is completely bogus. "Completely" means "for all". Are you seriously claiming that "for all instances of double-free, s

> The whole "prevent double free" claim is completely bogus. "Completely" means "for all". Are you seriously claiming that "for all instances of double-free, setting the pointer to NULL after freeing it would not help"?

lisper 1y ago
> "Completely" means "for all". Not in the case of bogosity. Completely bogus things might occasionally work under some very particular circumstances, but unless those particular circumstances just happen to be the circumstances you actually care about, complete bogosity can still obtain. > setting the pointer to NULL There is no such thing as setting a pointer to null. You can set the value of a variable (whose current value is a pointer) to null, but you cannot guarantee that there isn't a copy of the pointer stored somewhere else except in a few very particular circumstances. This is what the GP meant by "setting a variable to `NULL` only works for cases where there is one, obvious, owner". And, as the GP also pointed out, this "is not the circumstance under which double free is prone to happening in the first place." Hence: complete bogosity.
taneq 1y ago
Eeeeh, I don't think 'completely bogus' means 'exhaustively false for all situations'. It just means 'demonstrably false' (for some relatively sane example, we're talking about C after all which means there will always be bogus examples which break any given assumption). There's plenty of cases where zeroing a pointer immediately after freeing it will prevent any further issues. It's still bogus to claim that it categorically solves the problem of double frees. But it does help.
- tialaramex 1y ago
  Yeah. For example "Add four to it" is Completely Bogus way to implement "Multiply by three". Yes, if you had 2 then indeed 2 + 4 == 6 while the "more usual" 2 x 3 == 6, but for other values it doesn't work, it's Completely Bogus.

lisper 1y ago

> "Completely" means "for all". Not in the case of bogosity. Completely bogus things might occasionally work under some very particular circumstances, but unless those particular circumstances just happen to be the circumstances you actually care about, complete bogosity can still obtain. > setting the pointer to NULL There is no such thing as setting a pointer to null. You can set the value of a variable (whose current value is a pointer) to null, but you cannot guarantee that there isn't a copy of the pointer stored somewhere else except in a few very particular circumstances. This is what the GP meant by "setting a variable to `NULL` only works for cases where there is one, obvious, owner". And, as the GP also pointed out, this "is not the circumstance under which double free is prone to happening in the first place." Hence: complete bogosity.

taneq 1y ago

Eeeeh, I don't think 'completely bogus' means 'exhaustively false for all situations'. It just means 'demonstrably false' (for some relatively sane example, we're talking about C after all which means there will always be bogus examples which break any given assumption). There's plenty of cases where zeroing a pointer immediately after freeing it will prevent any further issues. It's still bogus to claim that it categorically solves the problem of double frees. But it does help.

tialaramex 1y ago
Yeah. For example "Add four to it" is Completely Bogus way to implement "Multiply by three". Yes, if you had 2 then indeed 2 + 4 == 6 while the "more usual" 2 x 3 == 6, but for other values it doesn't work, it's Completely Bogus.