为什么 char 不是单个字符? [英] Why is char not a single character?

问题描述

在 DEV_BROADCAST_DEVICEINTERFACE_A dbcc_name 的类型定义如下:

In Microsoft's documentation for DEV_BROADCAST_DEVICEINTERFACE_A the type of dbcc_name is defined as follows:

char  dbcc_name[1];

但如这个 StackOverflow 问题所示，结果是一个 string 带有 多个字符.

But as shown in this StackOverflow question it turns out to be a string with multiple characters.

char 不是 16 位值 单个字符吗?这是如何工作的?

Isn't a char a 16 bit value single character? How does this work?

_{(我原本以为 char 是 16 位.大概是因为这是它在 c# 中的大小.实际上可能是因为我在看 DEV_BROADCAST_DEVICEINTERFACE_W 其中确实是 2 个字节.)}

_{(I had originally thought that char is 16 bits. Presumably because that's its size in c#. Actually it was probably because I was looking at DEV_BROADCAST_DEVICEINTERFACE_W where it is indeed 2 bytes.)}

推荐答案

char 不是一个 16 位的值吗?

Isn't a char a 16 bit value?

在什么平台上?在大多数平台上(包括所有运行 Windows 的平台，AFAIK)，char 是 8 位.

On what platform? On most platforms (including all that run Windows, AFAIK), char is 8 bits.

这是如何工作的?

类型文档解释了这一点:

The type documentation explains this:

这个结构的大小，以字节为单位.这是成员的大小加上 dbcc_name 字符串的实际长度(空字符是通过将 dbcc_name 声明为单字符数组来考虑的.)

dbcc_size

The size of this structure, in bytes. This is the size of the members plus the actual length of the dbcc_name string (the null character is accounted for by the declaration of dbcc_name as a one-character array.)

换句话说，_DEV_BROADCAST_DEVICEINTERFACE_A的定义利用了C++中数组衰减为指针的事实，因此具有数组类型的dbcc_name可以用作大多数情况下以零结尾的字符串.实际字符串与 _DEV_BROADCAST_DEVICEINTERFACE_A 对象连续存储在从 dbcc_name 偏移量开始的地址处.

In other words, the definition of _DEV_BROADCAST_DEVICEINTERFACE_A exploits the fact that arrays decay to pointers in C++, and thus dbcc_name, which has array type, can be used as a zero-terminated string in most contexts. The actual string is stored contiguously with the _DEV_BROADCAST_DEVICEINTERFACE_A object, at the address starting at the offset of dbcc_name.

值得注意的是，数组(1)的大小与其内容的长度无关；它只是 C++ 中最小的合法静态数组大小(遗留代码偶尔会使用 char[0] 类型的结构成员.但是，这是编译器扩展而不是合法的 C++).

It’s worth noting that the size of the array (1) is unrelated to the length of its contents; it is simply the smallest legal static array size in C++ (legacy code occasionally uses struct members of type char[0]. However, this is a compiler extension and not legal C++).

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