PHP Chinese Character matching regular

Generally, there are two types of codes: UTF8 and GBK. Therefore, there are two types of matching codes (see the code configured for your website). <? Php
$ Action = trim ($ _ GET ['action']);
If ($ action = "sub ")
{
$ Str = $ _ POST ['dir'];
// If (! Preg_match ("/^ [". chr (0xa1 ). "-". chr (0xff ). "A-Za-z0-9 _] + $/", $ str) // GB2312 Regular Expression of Chinese characters, letters, numbers, underscores (_)
If (! Preg_match ("/^ [\ x {4e00}-\ x {9fa5} A-Za-z0-9 _] + $/u", $ str) // UTF-8 Chinese characters, letters, numbers, underscores, regular expressions
{
Echo "<font color = red> The [". $ str. "] You entered contains illegal characters </font> ";
}
Else
{
Echo "<font color = green> The [". $ str. "] You entered is completely legal. Pass! </Font> ";
}
}
?>