自己写的php中文截取函数mb_strlen和mb_substr_php实例

众所周知，php 自带的 strlen 与 substr 函数没法处理中文字符，于是，我们会用 mb_ 系列函数替代。但是，没有 mbstring 库怎么办？这就需要我们自己写一个来替代了，废话不多说，先上代码:

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] ++$s;
else {
++$s; // skip length

while ($str[$s] >= "\x80" && $str[$s] ++$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] ++$e;
else {
++$e;//skip length

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

return substr($str, $s, $e - $s);
}
}