十七、PHP去除string中的bom

<?php
/**
 * 该文件，旨在为了去除php string里的bom
 * bom存在的可能性有：1个或2个，
 * 1个的位置可能是： 首部，尾部，中间
 * 2个可能的位置是首部+尾部
 * @return $res['val']  即为最终的结果
 * @param $handle_ok 0代表仍有bom  1代表bom清除完毕
 */
$contents =    '13512340680 ';    //  This character contains 'bom'  226  128  172
//$contents =    '13812340919';   //
//$contents =    '15812349681 ';  //
//$contents =    '13712346524';   //
//$contents =    's13512340680';  //

//  Step 1:  trim
$contents = trim($contents);

function RemoveBom($contents,$handle_ok=0){
    //  Step 2:   extract the length of this str，judge it if contains 有bom(process)
    $length = strlen($contents);
    $have_bom = 0;
    // The position of bom
    $bom_position = 0;
    for($i=0;$i<$length;$i++){
        $temp_single_element = substr($contents,$i,1);
        $is_num = ord($temp_single_element);
        if( $is_num >= 48 && $is_num <= 57 ){
            //  no code in this line
        }else{
            $have_bom = 1;
            $bom_position = $i;
            break;
        }
    }

    // Step 3:  Judge if have bom(result), if have ,then remove it ：the position of bom： a. header b. footer  c. middle
    if($have_bom==1){
        // Judge header
        if($bom_position==0){
            //echo 'header';die;
            $res['handle_ok'] = 0 ;
            $res['val'] = substr($contents,3); // If no the third param, its default value is until to the tail of this string
            return $res ;
        // Judge footer
        }else if( $bom_position == ($length-3) ){
            //echo 'footer';die;
            $res['handle_ok'] = 0 ;
            $res['val'] = substr($contents,0,$length-3 );
            return $res ;
        // Judge middle
        }else {
            //echo 'middle';die;
            $starter = substr($contents,0,$bom_position );
            $ender   = substr($contents,$bom_position+3 );
            $res['handle_ok'] = 0 ;
            $res['val'] = $starter . $ender ;

            return $res ;
        }

    }else{
        // No bom
        $res['handle_ok'] = 1;
        $res['val'] = $contents;
        return $res ;
    }

}
$res = RemoveBom($contents);    // Remove the first one
$res = RemoveBom($res['val']);  // Remove the second one
$res = RemoveBom($res['val']);  // make $handle_ok become one
if($res['handle_ok']==1){
    var_dump($res);
    die;
}else{
    echo 'Still have bom';
    die;
}

// Judge if it is phone number with Regular Expression