自己写的php中文截取函数mb_strlen和mb_substr

if ( !function_exists('mb_strlen') ) {
function mb_strlen ($text, $encode) {
if ($encode=='UTF-8') {
return preg_match_all('%(?:
[\\x09\\x0A\\x0D\\x20-\\x7E] # ASCII
| [\\xC2-\\xDF][\\x80-\\xBF] # non-overlong 2-byte
| \\xE0[\\xA0-\\xBF][\\x80-\\xBF] # excluding overlongs
| [\\xE1-\\xEC\\xEE\\xEF][\\x80-\\xBF]{2} # straight 3-byte
| \\xED[\\x80-\\x9F][\\x80-\\xBF] # excluding surrogates
| \\xF0[\\x90-\\xBF][\\x80-\\xBF]{2} # planes 1-3
| [\\xF1-\\xF3][\\x80-\\xBF]{3} # planes 4-15
| \\xF4[\\x80-\\x8F][\\x80-\\xBF]{2} # plane 16
)%xs',$text,$out);
}else{
return strlen($text);
}
}
}

/* from Internet, author unknown */
if (!function_exists('mb_substr')) {
function mb_substr($str, $start, $len = '', $encoding="UTF-8"){
$limit = strlen($str);

for ($s = 0; $start > 0;–$start) {// found the real start
if ($s >= $limit)
break;

if ($str[$s] <= "\\x7F")
++$s;
else {
++$s; // skip length

while ($str[$s] >= "\\x80" && $str[$s] <= "\\xBF")
++$s;
}
}

if ($len == '')
return substr($str, $s);
else
for ($e = $s; $len > 0; –$len) {//found the real end
if ($e >= $limit)
break;

if ($str[$e] <= "\\x7F")
++$e;
else {
++$e;//skip length

while ($str[$e] >= "\\x80" && $str[$e] <= "\\xBF" && $e < $limit)
++$e;
}
}

return substr($str, $s, $e – $s);
}
}