PHP截取字符串函数【原创】

 
function cut_str($string, $sublen, $start = 0, $code = 'UTF-8', $ext = '') {
	if ($code == 'UTF-8') {
		$pa = "/[\x01-\x7f]|[\xc2-\xdf][\x80-\xbf]|\xe0[\xa0-\xbf][\x80-\xbf]|[\xe1-\xef][\x80-\xbf][\x80-\xbf]|\xf0[\x90-\xbf][\x80-\xbf][\x80-\xbf]|[\xf1-\xf7][\x80-\xbf][\x80-\xbf][\x80-\xbf]/";
		preg_match_all ( $pa, $string, $t_string );
		
		if (count ( $t_string [0] ) - $start > $sublen)
			return join ( '', array_slice ( $t_string [0], $start, $sublen ) ) . $ext;
		return join ( '', array_slice ( $t_string [0], $start, $sublen ) );
	} else {
		$start = $start * 2;
		$sublen = $sublen * 2;
		$strlen = strlen ( $string );
		$tmpstr = '';
		
		for($i = 0; $i < $strlen; $i ++) {
			if ($i >= $start && $i < ($start + $sublen)) {
				if (ord ( substr ( $string, $i, 1 ) ) > 129) {
					$tmpstr .= substr ( $string, $i, 2 );
				} else {
					$tmpstr .= substr ( $string, $i, 1 );
				}
			}
			if (ord ( substr ( $string, $i, 1 ) ) > 129)
				$i ++;
		}
		
		if (strlen ( $tmpstr ) < $strlen)
			$tmpstr .= $ext;
		return $tmpstr;
	}
}