Discuz X!的核心代码function_core.php里面有很多不错的样例，今天我们分析一个字符串切割函数，代码如下：

function cutstr($string, $length, $dot = ' ...') {
	if(strlen($string) <= $length) {
		return $string;
	}

	$pre = chr(1);
	$end = chr(1);
	$string = str_replace(array('&amp;', '&quot;', '&lt;', '&gt;'), array($pre.'&'.$end, $pre.'"'.$end, $pre.'<'.$end, $pre.'>'.$end), $string);

	$strcut = '';
	if(strtolower(CHARSET) == 'utf-8') {

		$n = $tn = $noc = 0;
		while($n < strlen($string)) {

			$t = ord($string[$n]);
			if($t == 9 || $t == 10 || (32 <= $t && $t <= 126)) {
				$tn = 1; $n++; $noc++;
			} elseif(194 <= $t && $t <= 223) {
				$tn = 2; $n += 2; $noc += 2;
			} elseif(224 <= $t && $t <= 239) {
				$tn = 3; $n += 3; $noc += 2;
			} elseif(240 <= $t && $t <= 247) {
				$tn = 4; $n += 4; $noc += 2;
			} elseif(248 <= $t && $t <= 251) {
				$tn = 5; $n += 5; $noc += 2;
			} elseif($t == 252 || $t == 253) {
				$tn = 6; $n += 6; $noc += 2;
			} else {
				$n++;
			}

			if($noc >= $length) {
				break;
			}

		}
		if($noc > $length) {
			$n -= $tn;
		}

		$strcut = substr($string, 0, $n);

	} else {
		$_length = $length - 1;
		for($i = 0; $i < $length; $i++) {
			if(ord($string[$i]) <= 127) {
				$strcut .= $string[$i];
			} else if($i < $_length) {
				$strcut .= $string[$i].$string[++$i];
			}
		}
	}

	$strcut = str_replace(array($pre.'&'.$end, $pre.'"'.$end, $pre.'<'.$end, $pre.'>'.$end), array('&amp;', '&quot;', '&lt;', '&gt;'), $strcut);

	$pos = strrpos($strcut, chr(1));
	if($pos !== false) {
		$strcut = substr($strcut,0,$pos);
	}
	return $strcut.$dot;
}

函数的作用可以切割所有html代码和各种编码的字符串，超过指定的长度后自动组合...成字符串返回。里面的每行代码都可以学习下！其中CHARSET是define的一个常量，比如define("CHARSET","UTF-8");