Some dict's idxHeader struct aren't packed in MSVC/Windows

[shenlebantongying]

Previous discussion #1573 (comment)

All idxHeader have gcc/clang's __attribute((packed))__, however, only some have its counterpart #pragma pack in MSVC.

This is not an issue because all data fields are currently 32 bits, MSVC will likely align the struct to 4 bytes, but this is unspecific/undefined behaviour. No idea if this already leads to bugs, or it will lead to bugs in the future, (or there is a standardized rule that I don't know and this is not a problem at all 😅 ).

https://github.com/search?q=repo%3Axiaoyifang%2Fgoldendict-ng%20idxHeader&type=code

Need more study to know if we can add alignas(4) for all idxHeader to ensure correctness.

[shenlebantongying]

Both clang & gcc supports #pragma pack(push, 1) -> #pragma pack(pop) since ages ago. There are no needs to do it twice, btw.

static_assert(alignof(S) == 1) can ensure extra correctness.

[xiaoyifang]

IMO， the pack feature should be used for cross-platform data migration. For example , move the windows index data to linux or vice versa.

[shenlebantongying]

cross-platform data migration

This feature needs "portable mode" or

• opt: unify dictionaryid #1446 😅