/**
 * PHP按字符截取中文并保证无乱码的方法
 *
 * @param 
 * @arrange 网： jb51.cc
 **/
//$str 待截取的字符串
//$len 截取的字符个数
//$chars 已经截取的字符数
//$res   保存的字符串
//$chars 保存已经截取的字符串个数
//$offset 截取的偏移量
//$length 字符串的字节数
//若$len>$str的字符个数，造成无谓的while循环，($offset<$length限定)
function utf8sub($str,$len){
	if($len<=0){
		return ;
	}
	$res="";
	$offset=0;
	$chars=0;
	$length=strlen($str);
	while($chars<$len && $offset<$length){
		$hign=decbin(ord(substr($str,$offset,1)));
			if(strlen($hign)<8){
				$count=1;
			}elseif(substr($hign,3)=="110"){
				$count=2;
			}elseif(substr($hign,4)=="1110"){
				$count=3;
			}elseif(substr($hign,5)=="11110"){
				$count=4;
			}elseif(substr($hign,6)=="111110"){
				$count=5;
			}elseif(substr($hign,7)=="1111110"){
				$count=6;
			}
		$res.=substr($str,$count);
		$offset+=$count;
		$chars+=1;
	}
	return $res;
}
function utf8sub1($str,$len){
	$chars=0;
	$res="";
	$offset=0;
	$length=strlen($str);
	while($chars<$len && $offset<$length){
		$hign=decbin(ord(substr($str,1)));
		if(strlen($hign)<8){
			$count=1;
		}elseif($hign & "11100000"=="11000000"){
			$count=2;
		}elseif($hign & "11110000"=="11100000"){
			$count=3;
		}elseif($hign & "11111000"=="11110000"){
			$count=4;
		}elseif($hign & "11111100"=="11111000"){
			$count=5;
		}elseif($hign & "11111110"=="11111100"){
			$count=6;
		}
		$res.=substr($str,$count);
		$chars++;
		$offset+=$count;
	}
	return $res;
}
$a="中华ah人民hdj";
echo utf8sub($a,5);
/***   来自编程之家 jb51.cc（jb51.cc）   ***/