Provides a platform-specific alternatecharacter used to separate directory levels in a path string that reflects a hierarchical file system organization.
提供平台特定的替换字符，该替换字符用于在反映分层文件系统组织的路径字符串中分隔目录级别。
2
When the character following the file mode bits is a space, there is no alternate access method.
当跟随文件模式位的字符是空格时，就表示没有替换访问方法。
3
This character specifies whether an alternate access method applies to the file.