基于linux的socket多线程通信方式。采用sqlite3数据库存储用户信息. 能够实现注册、登陆、退出 、私聊、群聊、修改密码、查看在线用户-Linux-based multi-threaded socket communication. Sqlite3 database to store user information. Achieve registration, login, exit, private chat, group chat, change passwords, vi