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And sorry for my late reply (just came back fr= om a short vacation). > On May 19, 2023, at 5:12 PM, Joseph Myers wrote= : >=20 > On Fri, 19 May 2023, Qing Zhao via Gcc-patches wrote: >=20 >> +GCC extension accepts a structure containing an ISO C99 @dfn{flexible a= rray >=20 > "The GCC extension" or "A GCC extension". Okay. >=20 >> +@item >> +A structure containing a C99 flexible array member, or a union containi= ng >> +such a structure, is the middle field of another structure, for example= : >=20 > There might be more than one middle field, and I think this case also=20 > includes where it's the *first* field - any field other than the last. Good point. Will fix this. >=20 >> +@smallexample >> +struct flex @{ int length; char data[]; @}; >> + >> +struct mid_flex @{ int m; struct flex flex_data; int n; @}; >> +@end smallexample >> + >> +In the above, @code{mid_flex.flex_data.data[]} has undefined behavior. >=20 > And it's not literally mid_flex.flex_data.data[] that has undefined=20 > behavior, but trying to access a member of that array. Yes, you are right. Will fix this. >=20 >> +Compilers do not handle such case consistently, Any code relying on >=20 > "such a case", and "," should be "." at the end of a sentence. Okay, will fix this. Thanks Qing >=20 > --=20 > Joseph S. Myers > joseph@codesourcery.com