strtotime（）期望参数1为字符串

I am write code in for loop , for multiple insert value using codeigniter framework .

this is my code

 $oldjoindate = $this->input->post('fldWorkHistoryJoiniedDate')  ;
$fldWorkHistoryJoiniedDate = date("Y-m-d", strtotime($oldjoindate));

for ($i=0; $i < count($fldWorkHistoryCompanyName); $i++) {
    $data5[] = array(

        'fldUserID' => $insert_id,
        'fldWorkHistoryCompanyName'=>$fldWorkHistoryCompanyName[$i],
        'fldWorkHistoryJoiniedDate'=>$fldWorkHistoryJoiniedDate[$i],
        //'fldWorkHistoryResignedDate'=>$fldWorkHistoryResignedDate[$i],
        'fldCompanyID' => $fldCompanyID

            );
  $this->db->insert_batch('tblWorkHistory',$data5);
}

Can Yo please check $fldWorkHistoryJoiniedDate this an array format like $fldWorkHistoryJoiniedDate[0],$fldWorkHistoryJoiniedDate[1] ?

$oldjoindate = $this->input->post('fldWorkHistoryJoiniedDate');
// check db data type is Date ?
$fldWorkHistoryJoiniedDate = date("Y-m-d", strtotime($oldjoindate));
// check date is coming proper 
// echo $fldWorkHistoryJoiniedDate;
for ($i=0; $i < count($fldWorkHistoryCompanyName); $i++) {
    $data5[] = array(
        'fldUserID' => $insert_id,
        'fldWorkHistoryCompanyName'=>$fldWorkHistoryCompanyName[$i],
        'fldWorkHistoryJoiniedDate'=>$fldWorkHistoryJoiniedDate[$i],
        //'fldWorkHistoryResignedDate'=>$fldWorkHistoryResignedDate[$i],
        'fldCompanyID' => $fldCompanyID
    );
  $this->db->insert_batch('tblWorkHistory',$data5);
}

// may be thisis not required $fldWorkHistoryJoiniedDate[$i] simple coming $fldWorkHistoryJoiniedDate