$_SERVER['SERVER_ADDR'] is not defined when using php as the built-in commandline web server, so you can not use $_SERVER['SERVER_ADDR'] to detect the Server's IP address.
P.S.: This is tested on Windows with PHP 7.1 on 2016-12-22.
Below is the printed $_SERVER variable.
Array
(
[DOCUMENT_ROOT] => E:\Programs\PHPServer\www\srv
[REMOTE_ADDR] => 118.117.61.32
[REMOTE_PORT] => 10865
[SERVER_SOFTWARE] => PHP 7.1.0 Development Server
[SERVER_PROTOCOL] => HTTP/1.1
[SERVER_NAME] => 0.0.0.0
[SERVER_PORT] => 8080
[REQUEST_URI] => /
[REQUEST_METHOD] => GET
[SCRIPT_NAME] => /index.php
[SCRIPT_FILENAME] => E:\Programs\PHPServer\www\srv\index.php
[PHP_SELF] => /index.php
[HTTP_HOST] => www.wuxiancheng.cn:8080
[HTTP_CONNECTION] => keep-alive
[HTTP_CACHE_CONTROL] => max-age=0
[HTTP_UPGRADE_INSECURE_REQUESTS] => 1
[HTTP_USER_AGENT] => Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/55.0.2883.87 Safari/537.36
[HTTP_ACCEPT] => text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8
[HTTP_DNT] => 1
[HTTP_ACCEPT_ENCODING] => gzip, deflate, sdch
[HTTP_ACCEPT_LANGUAGE] => zh-CN,zh;q=0.8,en-US;q=0.6,en;q=0.4
[HTTP_COOKIE] => qbbs_2132_saltkey=fZ7509n5; qbbs_2132_lastvisit=1482156014; Hm_lvt_f812a4362ef73c80c4d13485d1ab3a49=1482159614; _ga=GA1.2.1594404236.1482159615; su=727vL6EEPLqjcyfJcad-za9eVYOh1i7e; Hm_lvt_6a65b0f2004e441e86ecea9c3562d997=1482232509,1482241896,1482242293,1482296586
[REQUEST_TIME_FLOAT] => 1482390410.65625
[REQUEST_TIME] => 1482390410
)