PHP實現大數以,做分隔字元分隔

實現效果：類似1234567890-->1,234,567,890。

代碼：

//未考慮浮點型/*     * method 1     * echo number_format($str,2,'.',',');     */    /*  method2     *     先反轉字串strrev 再str_split($str,3);              $str = strrev($str);        $arr = str_split($str,3);//987        $res = '';        $count = count($arr);        while($count--){            $res .= strrev($arr[$count]).',';        }        $res = rtrim($res,',');    */    /*    method 3     *  截取出每3個字元     *  $count = strlen($str);        $i = 0;        $md = $count % 3;        switch ($md){            case 0:                break;            case 1:                $res = $str{0}.',';                $count -=1;                $i = 1;                break;            case 2:                $res = substr($str,0,2).',';                $count -= 2;                $i = 2;                break;        }        for(;$i<$count-3;$i+=3){            $res .= substr($str,$i,3).',';        }        $res .= substr($str,$i,3);    */    /*    method 4     *  正則，求不確定長度的做法        $md = strlen($str) % 3;        $res = substr($str, 0,$md).($md == 0?'':',');         $res .= preg_replace('(\d{3})', '\\0,', substr($str, $md));        $res = rtrim($res,',');    */