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Added description and URL about nested flexible array member.
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卜部昌平 2020-09-25 10:21:45 +09:00
parent 4cc501bcfd
commit c6c241e49c
Notes: git 2020-09-25 11:39:03 +09:00
1 changed files with 13 additions and 4 deletions
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17
include/ruby/internal/stdalign.h
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@ -112,10 +112,19 @@ struct rbimpl_alignof {
# define RBIMPL_ALIGNOF __alignof
#else
# /* :BEWARE: It is an undefined behaviour to define a struct/union inside of
# * `offsetof()`! This section is the last resort. If your compiler somehow
# * supports querying alignment of a type please add your own definition of
# * `RBIMPL_ALIGNOF` instead. */
# /* :BEWARE: This is the last resort. If your compiler somehow supports
# * querying the alignment of a type, you definitely should use that instead.
# * There are 2 known pitfalls for this fallback implementation:
# *
# * Fitst, it is either an undefined behaviour (C) or an explicit error (C++)
# * to define a struct inside of `offsetof`. C compilers tend to accept such
# * things, but AFAIK C++ has no room to allow.
# *
# * Second, there exist T such that `struct { char _; T t; }` is invalid. A
# * known example is when T is a struct with a flexible array member. Such
# * struct cannot be enclosed into another one.
# */
# /* see: http://www.open-std.org/jtc1/sc22/wg14/www/docs/n2083.htm */
# /* see: http://www.open-std.org/jtc1/sc22/wg14/www/docs/n2350.htm */
# define RBIMPL_ALIGNOF(T) offsetof(struct { char _; T t; }, t)