问题
In C, I saw some usage of offsetof to calculate the offset of a member in the structure to its beginning?
Is it still recommended to use in C++? Any other way to do this without this macro?
回答1:
C++ has pointers to members. These are similar to offsets, but (1) typesafe and (2) more generic - they also work with methods, on base classes, etc.
回答2:
Offsetof is a feature that is only in the C++ standard for C compatibility so it is not reccomended to be used in C word
回答3:
I wouldn't recommend it for anything, unless you really need to. So long as your use is valid in C, it should be valid for C++. Without knowing what you are doing, your question is impossible to answer.
回答4:
No, it's not.
Proper C++ style encourages user to avoid all low-level details when possible. This is both for safety/correctness and readability. Only when low-level manipulation guarantees real and significant performance improve should one jump into it.
回答5:
One of the usages of offsetof() was in C-like code having structures with a fixed header, and variable size arrays, like explained in this blog post:
Why do some structures end with an array of size 1?
(Note that this blog post uses the FIELD_OFFSET macro, which is a Windows-ism, corresponding to offsetof().)
I think in modern C++ we should use higher-level techniques and code, like std::vector for variable sized arrays.
来源：https://stackoverflow.com/questions/22716560/about-offsetof-usage-in-c-and-c