"Offset of on non-standard-layout type" warning on new SDK (C++) in Xcode

[AlexHarker]

Since moving to max-sdk-base (from the old max-sdk, prior to this separation) I've been getting these warnings about macros like:

CLASS_ATTR_SYM

in Xcode where the max object is a C++ object (I'm not using the min-api I have my own C++ wrapper). The warning does not occur for exactly the same code if I switch back to the old SDK, so it's related to the SDK, and not Xcode version/compiler etc. I cannot find any relevant pragmas that would have previously been suppressing the warning, nor do my types have any virtual methods.

Everything still works as expected, but it is a bit tedious - do you have any pointers for why this might have changed and if I can suppress the warnings?

[AlexHarker]

Ah - I see that the definition of calcoffset has changed from:

#define calcoffset(x,y) ((t_ptr_int)(&(((x *)0L)->y)))

to

#define calcoffset(x,y) offsetof(x, y)

(where offsetof() will map to __builtin_offsetof).

That explains why it happens, so I guess this may cause warnings for anyone making externals as C++ objects, whether using min-api or not.

[superbigio]

Yes, it does cause warnings for all the CLASS_ATTR macros (since they all use the calcoffset macro under the hood) which is harmless but very annoying...
It could be trivially solved by declaring:

#define calcoffset(x,y) ((t_ptr_int)offsetof(x, y))

But I don't know if the C74 folks will ever make this change, and I don't feel like spending the time to create a pull request that might be ignored. As you can clearly see C74 is not very responsive to this kind of SDK related bugs.

On a more general note the habit of using unsigned integers for sizes and quantities is absolutely wrong.
Unfortunately the C++ std library declares size_t as unsigned and therefore it's hard to escape the pitfall.

[AlexHarker]

FWIW - I am currently using -Wno-invalid-offsetof in my configs which suppresses the warning. The warning is technically correct due to the very narrow definition of a POD type in the C++ standard, but in practice the types I am using are safe to use offsetof() on.

I'm not sure of the relevance of unsigned integers to this issue.