1.__DIR__:系统预定义魔术变量
2.define、const定义常量
3.include、requre引用文件
4.microtime()
var_dump(microtime());
//输出string(21) "0.39244700 1652063929"5.php输出
https://www.cnblogs.com/perseverancevictory/p/4254796.html
6.memory_get_usage():
7.defined()函数
8.strtr
9.property_exists
10.null
经测试，用is_null()判断一个未声明的变量，其值为true.
11.file_get_contents:
12.php://input
13.new self() 与 new static()的区别
https://blog.csdn.net/weixin_29186249/article/details/115157295
14.php预定义数组
15.global:
16.basename:
17.str_replace
18.rtrim():
19.function_exists()
20.apache_request_header()
21.array_change_key_case():
22.reset()
23.gmdate()
