什么是下面的宏吗？ [英] What does the following macro do?

问题描述

在QEMU源$ C ​​$ C，我有一个名为以下，宏offsetof 。谁能告诉我这是什么呢？

in qemu source code, I have the following macro named offsetof. Can anybody tell me what it does?

#define offsetof(TYPE, MEMBER) ((size_t) &((TYPE *) 0)->MEMBER)

它以这种方式使用：

It's used in this manner :

offsetof(CPUState, icount_decr.u32)

其中CPUState是一个结构。

where CPUState is a struct.

我觉得它给一个结构内部成员的偏移，但我不知道。

I think it gives the offset of the member inside a struct, but I'm not sure.

编辑：是啊，我发现发生了什么事。 CPUState的定义有一个宏里，我错过了，其中包括可变icount_decr。

Yeah, I found out what was happening. The definition of CPUState had a macro inside, which I missed, which included the variable icount_decr.

推荐答案

它得到的偏移结构的成员。它通过铸造零地址的类型，然后取件的地址的结构这样做。

It gets the offset of the member of a struct. It does so by casting address zero to a struct of that type then taking the address of the member.

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