为什么 UTF-8 是这样编码的？
如果我理解正确的话，UTF-8使用以下模式让计算机知道将使用多少个字节来编码一个字符：
| Byte 1 | Byte 2 | Byte 3 | Byte 4 |
|---|---|---|---|
| 0xxxxxxx | |||
| 110xxxx | 10xxxxxx | ||
| 1110xxxx | 10xxxxxx | 10xxxxxx | |
| 11110xxx | 10xxxxxx | 10xxxxxx | 10xxxxxx |
等等。但是没有更紧凑的模式吗？例如，是什么阻止我们使用这样的东西：
| Byte 1 | Byte 2 | Byte 3 | Byte 4 |
|---|---|---|---|
| 0xxxxxxx | |||
| 10xxxxxx | xxxxxxxx | ||
| 110xxxxxx | xxxxxxxx | xxxxxxxx | |
| 1110xxxx | xxxxxxxx | xxxxxxxx | xxxxxxxx |
If I understood correctly, UTF-8 uses the following pattern to let the computer know how many bytes are going to be used to encode a character:
| Byte 1 | Byte 2 | Byte 3 | Byte 4 |
|---|---|---|---|
| 0xxxxxxx | |||
| 110xxxxx | 10xxxxxx | ||
| 1110xxxx | 10xxxxxx | 10xxxxxx | |
| 11110xxx | 10xxxxxx | 10xxxxxx | 10xxxxxx |
Etc. But aren't there more compact patterns? For instance, what is stopping us from using something like this:
| Byte 1 | Byte 2 | Byte 3 | Byte 4 |
|---|---|---|---|
| 0xxxxxxx | |||
| 10xxxxxx | xxxxxxxx | ||
| 110xxxxx | xxxxxxxx | xxxxxxxx | |
| 1110xxxx | xxxxxxxx | xxxxxxxx | xxxxxxxx |
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评论（1）
您建议的编码不会自同步。如果您落在流的中间
xxxxxxxx字节上，您将不知道它是否位于字符的中间。如果该随机字节恰好是10xxxxxx，您可能会将其误认为是字符的开头。避免此错误的唯一方法是从头开始无错误地读取整个流。自同步是 UTF-8 的明确目标。如果您到达 UTF-8 流中的任何位置，您知道是否位于字符的中间，并且最多需要读取 3 个字节才能找到完整字符的下一个开头。
Your proposed encoding wouldn't be self-synchronizing. If you landed in the middle of a stream on an
xxxxxxxxbyte, you'd have no idea whether it's in the middle of a character or not. If that random byte happened to be10xxxxxx, you could mistake it for the start of a character. The only way to avoid this mistake is to read the entire stream error free from the beginning.It's an explicit goal for UTF-8 to be self-synchronizing. If you land anywhere in a UTF-8 stream, you know whether you're in the middle of a character or not, and need to read at most 3 bytes to find the next start of a full character.