After following, you can keep track of his dynamic information in a timely manner
Courses in the relevant section：Variable types and detection techniques (Part 1)
is_null():检测未声明的变量 empty():检测变量是否为空值 isset():检测变量是否为已声明，可视为is_null()的逆操作 unset()后的变量要用isset()来检测
2018-10-220个赞
