[flag#String](https://link.segmentfault.com/?enc=n6f6iRAxnjBPFVXe9mJA6Q%3D%3D.Pmq6QMUxUW8j6EXTBzTajemD8aEEr5BCv4McnrpiueE%3D) > `String` defines a string flag with specified name, default value, and usage > string. The return value is the address of a string variable that stores the > value of the flag. 返回的是一个字符串指针,里面会存储提取出的 flag 的值。