4 ms·

Even better and simpler.. Payload *item = (Payload *)malloc(offsetof(Payload, elements[N])); The rest of the article does make me vary of a lot of other thi

• kazinator 1y ago
  That's really great; it's easy to forget that the second argument of offsetof isn't simply a member name, but a designator expression.
• kazinator 1y ago
  Unfortunately, ISO C requires offsetof to calculate a constant; moreover, the right operand is a "member designator", which elements[N] isn't. However, the traditional (and pretty much the only sensible) ways of defining offsetof do make it work. N3220 draft: offsetof(type, member-designator) [expands] to an integer constant expression that has type size_t, the value of which is the offset in bytes, to the subobject (designated by member-designator), from the beginning of any object of type type. The type and member designator shall be such that given static type t; then the expression &(t. member-designator) evaluates to an address constant. If the specified type name contains a comma not between matching parentheses or if the specified member is a bit-field, the behavior is undefined. This doesn't mean I won't use it, but just something to be aware of. It might not be a bad idea to propose to ISO C that offsetof(type, array[n]) should be required to work, and for non-constant n too.
  • kazinator 1y ago
    In GCC, __builtint_offsetof explicitly supports the extended syntax for the member designator. when the offsetof macro uses __builtin_offsetof, the capability is a documented extension.