内存映射文件的功能之一就是将磁盘上的整个文件读入内存，应用程序直接访问这块内存就相当于访问文件的内容了。这对于从比较大的文件中读信息来说相当方便。-memory mapping document is one of the functions of disk read the entire document into memory, Application procedures directly to the memory of this visit is equivalent to the c