设置服务器的MySQL允许远程访问/外网访问

mysql -uroot -p

use mysql;

update user set host='%' where user='root' and host='localhost';

exit

sudo service mysql restart

#define DATABASE_URL "tcp://123.xxx.xx.xxx"
#define DATABASE_USER "root"
#define DATABASE_PWD "123456"
...
/* 创建连接 */
driver = get_driver_instance();
con = driver->connect(DATABASE_URL, DATABASE_USER, DATABASE_PWD);