[PHP] Upgrade from 5.4 to 7.4

Encountered problems with encoding, database connection, etc.

<?php
header("Content-type:text/html;charset=GB2312");
echo $str= '你好,这里是gbk转utf8!';
echo '<br />';
echo iconv('GB2312', 'UTF-8', $str); //将字符串的编码从GB2312转到UTF-8

From: https://www.php.cn/faq/462796.html