php按字符无乱码截取中文的方法

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<?php

//$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,0,3)=="110"){

$count=2;

}elseif(substr($hign,0,4)=="1110"){

$count=3;

}elseif(substr($hign,0,5)=="11110"){

$count=4;

}elseif(substr($hign,0,6)=="111110"){

$count=5;

}elseif(substr($hign,0,7)=="1111110"){

$count=6;

}

$res.=substr($str,$offset,$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,$offset,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,$offset,$count);

$chars++;

$offset+=$count;

}

return $res;

}

$a="中华ah人民hdj";

echo utf8sub($a,5);

?>