字符串长度截取函数

支持计算英文、空格、数字~

//截取字符function cut_str($sourcestr,$cutlength, $start=0,$dot=''){$returnstr = '';$i = 0;$n = 0;$str_length = strlen($sourcestr);$mb_str_length = mb_strlen($sourcestr,'utf-8');while(($n < $cutlength) && ($i <= $str_length)){$temp_str = substr($sourcestr,$i,1);$ascnum = ord($temp_str);if($ascnum >= 224){$returnstr = $returnstr.substr($sourcestr,$i,3);$i = $i + 3;$n++;}elseif($ascnum >= 192){$returnstr = $returnstr.substr($sourcestr,$i,2);$i = $i + 2;$n++;}elseif(($ascnum >= 65) && ($ascnum <= 90)){$returnstr = $returnstr.substr($sourcestr,$i,1);$i = $i + 1;$n++;}else{$returnstr = $returnstr.substr($sourcestr,$i,1);$i = $i + 1;$n = $n + 0.5;}}if ($mb_str_length > $cutlength){$returnstr = $returnstr.$dot;}return $returnstr;}