先创建一个大文件,然后一点一点往其中添加字节的例子,与网络下载工具创建文件的方式相同,非常适合初学者学习文件操作API-first create a large file, and then point to 1.1 gigabytes of which add example, and network tools to create documents downloaded in the same way, very suitable for beginners learning file m