Question2.19:What's the difference between a structure and a union,anyway?

那个谁

Q: What's the difference between a structure and a union, anyway?
A: A union is essentially a structure in which all of the fields overlay each other; you can only use one field at a time. (You can also cheat by writing to one field and reading from another, to inspect a type's bit patterns or interpret them differently, but that's obviously pretty machine-dependent.) The size of a union is the maximum of the sizes of its individual members, while the size of a structure is the sum of the sizes of its members. (In both cases, the size may be increased by padding; see questions 2.12 and 2.13.)     

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问题：一个结构体和一个联合体的区别是什么？
回答：一个联合体在本质上是一个结构体，只是它们的位域是重叠的；你一次只能使用一个位域（你也可以写入一个位域然后从另一个位域读取，来检测某种类型的二进制模式或者用不同的方式解释他们，当然这些都与机器相关联）。联合体的大小是单个成员中最大的那个所占的大小，而一个结构体的大小则是所有成员大小的总和（这两种情况，空间大小都可能被填充而增加；参考问题2.12和2.13。）。