During CSV downloading - Warning: Cannot modify header information - headers already sent by (output started at

Question

The following small demo code is running successfully

<?php
$list = array
(
"ID,Name,Preview,Payout",
"Peter,Griffin,Oslo,Norway",
"Glenn,Quagmire,Oslo,Norway",
);
$today_doc=date("Y-m-d").".csv";
$file = fopen($today_doc,"w");

foreach ($list as $line)
  {
  fputcsv($file,explode(',',$line));
  }
  fclose($file); 
// We'll be outputting a csv
header('Content-type: text/csv');
// It will be called contacts.csv
header('Content-Disposition: attachment; filename="'.$today_doc.'"');
// The PDF source is in original.csv
readfile($today_doc);?>

I used the above demo code to my script then its not working. Saying-> Warning: Cannot modify header information - headers already sent by (output started at

    $selected_ids=$_POST['selected_id'];
    $xyz="";
    $list = array
    ("ID,Offer Name,Emp,salary");
    $i=0;
    foreach($selected_ids as $id)
        {
            $xyz.=$id.',';
        }
        $xyz=trim($xyz,',');
    $extract=mysqli_query($con,"SELECT * FROM `emp_record` WHERE id in ($xyz)") or die(mysqli_error($con));
    while($row = mysqli_fetch_array($extract))
    {
        $i++;
        $list[$i]=$row["id"].','.$row["name"].','.$row["emp"].','.$row["salary"];
    }
$today_doc=date("Y-m-d").".csv";
$today_doc="contacts.csv";
$file = fopen($today_doc,"w");
foreach ($list as $line)
  {
  fputcsv($file,explode(',',$line));
  }
  fclose($file);
  //  We'll be outputting a csv
 header('Content-type: text/csv');
// It will be called contacts.csv
header('Content-Disposition: attachment; filename=contacts.csv');
//The PDF source is in original.csv
readfile("contacts.csv");
}

Can anyone please help to resolve the issue.

Answer 1

Put header functions before any echo/output:

<?php
header('Content-type: text/csv');
header('Content-Disposition: attachment; filename=contacts.csv');

EDITED:

oh, this was not your question, but if you want like this you should echo this headers "header('Content-type: text/csv');header('Content-Disposition: attachment; filename=contacts.csv');" and then load csv from file in some var eg. "$csv", and then Just echo content, something like:

<?php
header('Content-type: text/csv');
header('Content-Disposition: attachment; filename=contacts.csv');
$csv = file_get_contents('YOUR  PATH');
echo $csv;
exit;

Answer 2

You will always get this error "Warning: Cannot modify header information - headers already sent" when

1. you leave a blank line before

2. if the call was an ajax call and you echoed some characters before calling the header.

Just mak sure the is no character before

Answer 3

You can add:

ob_start() at start

and

ob_flush() at end

Example:

<?php ob_start(); ?>
<?php
    header('Content-Type: text/csv; charset=utf-8');
    header('Content-Disposition: attachment; filename=export.csv');
     .......
     ob_flush();
?>

Note

If you want, you can use:

ob_start("ob_gzhandler")

ob_gzhandler() is intended to be used as a callback function for ob_start() to help facilitate sending gz-encoded data to web browsers that support compressed web pages.

You see:

PHP net ob_start

and

PHP net ob_gzhandler