When the device was connected to the cloud service, I encountered a problem with the Chinese character code in the Mysql database. After checking the information online, I finally solved it. Special record:
C for linux
mysql_query(conn_ptr,"set character_set_results=utf8"); //读库
Read data....
mysql_query(conn_ptr,"set names 'utf8'");//写库
Insert data/modify data...
PHP
mysql_query("set names 'UTF8'");
Insert data/read data/modify data
...