php outbuffering and header - php

Question

I am using php 5.3.6 and below is my code and it is producing an error
Warning: Cannot modify header information - headers already sent by (output started at ............
<?php
ob_implicit_flush(true);
print "<pre>";
$loop = true;
$counter = 0;
while ($loop) {
$counter++;
// some code
print "some output of code. \n";
if ($elapsedTime > 300) {
$loop = false;
print "5 minute passed and loop ended. \n";
}
}
print "</pre>";
ob_end_flush();
header("refresh:5;url=test.php" );
?>
what I wanted to do is displays contents from each loop while the loop is active.
then when the loop is ended I need to flush all the previous output or header and send a new header to refresh the current page.

Answer 1

The short version is, you can't. You can not send headers after the content.
You could print out a link at the end, that the user can click on to refresh the page. Or if the generation will take a fixed amount of time (say 5 minutes) you could put an HTML meta refresh tag on the page that goes after 5 minutes and 1 second.
http://en.wikipedia.org/wiki/Meta_refresh
Header redirects generally take the form Location: ?test.php, if there's a new format that looks just like the meta refresh format, I'm not aware of it, and it would seem to violate how the other headers work (namely key: value). Short version: I don't think that header will work even if it does go first.

Answer 2

As suggested by preinheimer the header must be sended before each page ouput. Without using the headers you can use one row of javascript code for a simple redirect. This may be a solution for you:
<?php
print "<pre>";
$loop = true;
$counter = 0;
while ($loop) {
$counter++;
// some code
print "some output of code. \n";
if ($elapsedTime > 300) {
$loop = false;
print "5 minute passed and loop ended. \n";
}
}
print "</pre>";
# The php code has ended and the javascript code is ready for redirecting... (external to php tags)
?>
<script type="text/javascript">
window.location="http://www.example.com/";
</script>