unicode values in phpexcel are not exporting - php

Question

I am trying to export unicode values to excel using phpexcel.
The code works perfectly in my localhost but when uploaded to live it is giving junk values.
Framework used : Codeigniter
Server : CENTOS 6.9 , php7, easy Apache 4.
public function export_approvedApplication() {
error_reporting(E_ALL);
ini_set('display_errors', 1);
//load our new PHPExcel library
$this->load->library('excel');
//activate worksheet number 1
$this->excel->setActiveSheetIndex(0);
//name the worksheet
$this->excel->getActiveSheet()->setTitle('Taluk Excel');
//make the font become bold
$this->excel->getActiveSheet()->getStyle('A1')->getFont()->setBold(true);
$this->excel->getActiveSheet()->getStyle('B1')->getFont()->setBold(true);
$output = 'ಹೆಸರು';
//$output = mb_convert_encoding($output, 'UTF-16LE', 'UTF-8');
//$output = utf8_encode($output);
$content_array = array(array('SL No', $output));
// read data to active sheet
$this->excel->getActiveSheet()->fromArray($content_array);
$filename = 'ExportEXCEL.xls'; //save our workbook as this file name
header('Content-Encoding: UTF-8');
header('Content-Type: application/vnd.ms-excel; charset=UTF-8'); //mime type
header('Content-Disposition: attachment;filename="' . $filename . '"'); //tell browser what's the file name
header('Cache-Control: max-age=0'); //no cache
//save it to Excel5 format (excel 2003 .XLS file), change this to 'Excel2007' (and adjust the filename extension, also the header mime type)
//if you want to save it as .XLSX Excel 2007 format
$objWriter = PHPExcel_IOFactory::createWriter($this->excel, 'Excel5');
//force user to download the Excel file without writing it to server's HD
$objWriter->save('php://output');
}
I have also tried with 'mb_convert_encoding' but was unsuccessfull as it was giving
Call to undefined function mb_convert_encoding()
Then I tried installing mbstring , however I was not able to do the same.
Local environment : ubuntu 16 , php7
It would be of great help if anyone could help me with this.
Thank you

Answer 1

Issue is fixed.
#Mark and #Gaurav : Thank you so guys for your suggestions and prompt replies.
As I have mentioned above in my post and in my replies I was not able to render unicode values in my excel export using PHPEXCEL .
After googling much and using 'mb_convert_encoding' I found that I have to enable mbstring extension . For doing that I tried using terminal (used 'yum install php56-mbstring' , 'used REPO', 'tried download') I dont know why but could not succeed in the same.
Then I could enable the mbstring only using WHM login
I followed the link below
LINK HERE
Thank you