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Comment by wheybags | Hacker News Reader

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wheybags·

I have unironically used `#define private public` before including headers in my test code...

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Well, I hope you know that in theory it's undefined behavior, and in practice it can actually affect layout of objects.

Why is it undefined behavior?

It looks like it's a C++ standard library requirement:

https://eel.is/c++draft/macro.names#2

Otherwise this is one of the unintended effects (on Itanium ABI):

https://godbolt.org/z/bY4534zhc

FYI, MSVC doesn't do this. I use this same hack in a project where I need access to private/protected members in the current stage, and memory layouts need to match ... You gave me a bit of a heart attack there.

mingw gcc (11.2.0) does have the same 8 vs 12 difference.

MSVC might not alter layout, but public and private member functions have different name mangling:

https://godbolt.org/z/ddqd3vr5x

Notice the call to `?foo@A@@AEAAXXZ` in one compilation and `?foo@A@@QEAAXXZ` in the other, supposedly to the same function. You might get fun linker errors this way, possibly nothing nastier though.

Yeah, I'm aware of that. I've had to edit mangled names a few times too many - transferring between idbs and changing const char * to char * (PBD to PAD I think? thankfully I'm already not sure anymore), for example. Or changing __int64 to int ...

Luckily I don't need to link anything, so I don't care about that for now.

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