php判断中文和编码有关 gbk是双字节，utf8是三字节，可以根据 中文的范围来判断

编码范围1. GBK (GB2312/GB18030)
\x00-\xff GBK双字节编码范围
\x20-\x7f ASCII
\xa1-\xff 中文
\x80-\xff 中文
2. UTF-8 (Unicode)
\u4e00-\u9fa5 (中文)
\x3130-\x318F (韩文
\xAC00-\xD7A3 (韩文)
\u0800-\u4e00 (日文)
ps: 韩文是大于[\u9fa5]的字符
正则例子:
preg_replace(”/([\x80-\xff])/”,”",$str);
preg_replace(”/([u4e00-u9fa5])/”,”",$str);
二、代码例子

 
//判断内容里有没有中文-GBK (PHP) 
function check_is_chinese($s){ 
return preg_match('/[\x80-\xff]./', $s); 
} 
//获取字符串长度-GBK (PHP) 
function gb_strlen($str){ 
$count = 0; 
for($i=0; $i<strlen($str); $i++){ 
$s = substr($str, $i, 1); 
if (preg_match("/[\x80-\xff]/", $s)) ++$i; 
++$count; 
} 
return $count; 
} 
//截取字符串字串-GBK (PHP) 
function gb_substr($str, $len){ 
$count = 0; 
for($i=0; $i<strlen($str); $i++){ 
if($count == $len) break; 
if(preg_match("/[\x80-\xff]/", substr($str, $i, 1))) ++$i; 
++$count; 
} 
return substr($str, 0, $i); 
} 
//统计字符串长度-UTF8 (PHP) 
function utf8_strlen($str) { 
$count = 0; 
for($i = 0; $i < strlen($str); $i++){ 
$value = ord($str[$i]); 
if($value > 127) { 
$count++; 
if($value >= 192 && $value <= 223) $i++; 
elseif($value >= 224 && $value <= 239) $i = $i + 2; 
elseif($value >= 240 && $value <= 247) $i = $i + 3; 
else die('Not a UTF-8 compatible string'); 
} 
$count++; 
} 
return $count; 
} 
//截取字符串-UTF8(PHP) 
function utf8_substr($str,$position,$length){ 
$start_position = strlen($str); 
$start_byte = 0; 
$end_position = strlen($str); 
$count = 0; 
for($i = 0; $i < strlen($str); $i++){ 
if($count >= $position && $start_position > $i){ 
$start_position = $i; 
$start_byte = $count; 
} 
if(($count-$start_byte)>=$length) { 
$end_position = $i; 
break; 
} 
$value = ord($str[$i]); 
if($value > 127){ 
$count++; 
if($value >= 192 && $value <= 223) $i++; 
elseif($value >= 224 && $value <= 239) $i = $i + 2; 
elseif($value >= 240 && $value <= 247) $i = $i + 3; 
else die('Not a UTF-8 compatible string'); 
} 
$count++; 
} 
return(substr($str,$start_position,$end_position-$start_position)); 
} 
//判断是否是有韩文-UTF-8 (JavaScript) 
function checkKoreaChar(str) { 
for(i=0; i<str.length; i++) { 
if(((str.charCodeAt(i) > 0x3130 && str.charCodeAt(i) < 0x318F) || (str.charCodeAt(i) >= 0xAC00 && str.charCodeAt(i) <= 0xD7A3))) { 
return true; 
} 
} 
return false; 
} 
//判断是否有中文字符-GBK (JavaScript) 
function check_chinese_char(s){ 
return (s.length != s.replace(/[^\x00-\xff]/g,"**").length); 
}