PHP Unconference Europe 2015

ob_flush

(PHP 4 >= 4.2.0, PHP 5)

ob_flushFlush (send) the output buffer

Descrizione

void ob_flush ( void )

This function will send the contents of the output buffer (if any). If you want to further process the buffer's contents you have to call ob_get_contents() before ob_flush() as the buffer contents are discarded after ob_flush() is called.

This function does not destroy the output buffer like ob_end_flush() does.

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User Contributed Notes 12 notes

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20
Lee
2 years ago
As of August 2012, all browsers seem to show an all-or-nothing approach to buffering. In other words, while php is operating, no content can be shown.

In particular this means that the following workarounds listed further down here are ineffective:

1) ob_flush (),  flush () in any combination with other output buffering functions;

2) changes to php.ini involving setting output_buffer and/or zlib.output_compression to 0 or Off;

3) setting Apache variables such as "no-gzip" either through apache_setenv () or through entries in .htaccess.

So, until browsers begin to show buffered content again, the tips listed here are moot.
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15
dermeister dot online at gmail dot com
2 years ago
some problems with ob_flush() and flush() could be resolved by defining content type header :
header( 'Content-type: text/html; charset=utf-8' );

so working code looks like this:
<?php
header
( 'Content-type: text/html; charset=utf-8' );
echo
'Begin ...<br />';
for(
$i = 0 ; $i < 10 ; $i++ )
{
    echo
$i . '<br />';
   
flush();
   
ob_flush();
   
sleep(1);
}
echo
'End ...<br />';
?>
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1
cesoid at gmail dot com
1 year ago
Currently I have Chrome on OS X Snow Leopard updating a page as it is sent more data, BUT it only does this after I send it <body> along with 1013 more characters (making 1019 total characters). After it receives this it immediately displays it and then displays anything else as it is received. (Note that this browser-operating system combination isn't necessarily the only one, it's just the only one I've tested.)

In order to do this using php, I've done nothing but send ob_flush() after each echo or print. I can also make it happen without ob_flush() by calling ob_implicit_flush(), then ob_end_flush() before print, and then it updates with each print after that. I have pretty typical settings and I change none of them when the file runs, it literally looks like this:

<?php
  ob_implicit_flush
();
 
ob_end_flush();
 
?><body>[1013 more characters]<?php
 
for ($i = 1; $i < 30000000; ++$i) {}
  echo
"something that didn't show up immediately";
?>

(Ok, the "[1013 more characters]" part wasn't strictly literal.)

If you want just text in the browser, you do this before everything else:

<?php
header
("Content-type: text/plain");
...
?>

Then it won't care whether you sent a body tag, it will just wait for 1019 characters.
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2
Anonymous
9 years ago
You must call them in the correct order.
ob_flush();
flush();
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1
Anonymous
9 years ago
I was having problems with output buffering which seemed to be active by default on the server, although phpinfo said something else..

In any case I needed to know that when I ran ob_start, it would start at the top level, so I could use ob_flush as it's intended without having to call multiple ob_flush in-script - this is what I did:

<?php

// make sure output buffering is off before we start it
// this will ensure same effect whether or not ob is enabled already
while (ob_get_level()) {
   
ob_end_flush();
}
// start output buffering
if (ob_get_length() === false) {
   
ob_start();
}

?>

Then I could call ob_flush(); followed by flush(); and get the output I wanted, which I didn't if I started the script with just ob_start();

This was on a windows apache 2 server with php 5.0.4 btw.
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2
Jens
6 years ago
If you call ob_flush() and flush() and still dont get the buffer flushed it might be because some antivirus software (Panda in this case) holds the buffer until the page has finished loaded before sending it to the browser.
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1
colnector at@ colnect punto com
6 years ago
As stated in flush() manual entry, if php compresses the ouput with zlib this function may be ineffective.

A possible option for folders on your server that have scripts which may take a long time to run is to add the following in your relevant .htaccess file:

<FilesMatch "\.(php|html?)$">
php_flag zlib.output_compression off
php_value max_execution_time 3000
php_value max_input_time 3000
</FilesMatch>
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0
riimeik
4 years ago
If you're still not getting the buffer work correctly then try to clean all the others before starting your own (and even if PHP tells you that there are no buffers active):

while(@ob_end_clean());
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0
sebastian at jcompare dot com
5 years ago
For some reason, calling just flush or ob_flush or even both together did not get my output buffers flushed, and calling ob_end_flush by itself didn't work either but calling them all worked well. Here is my new output flushing function.

<?php
function flush_buffers(){
   
ob_end_flush();
   
ob_flush();
   
flush();
   
ob_start();
}
?>

Enjoy
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0
Reynard Hilman
9 years ago
when using command line php, if somewhere in your script you have ob_start(), you have to call ob_end_flush() first, and then you can call these functions:
flush();
ob_flush();

without calling ob_end_flush first, flush and ob_flush does not have any effect, at least that's what I experienced.
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0
jeremy at e2-media dot co dot nz
9 years ago
we had problems with flushing data to the browser. a simple call to ob_flush() or flush() would not work. We found that repeatly calling theses fuctions did work however.

<?
flush();
ob_flush();
flush();
ob_flush();
flush();
ob_flush();
?>

go figure!
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-3
kel at no-spam dot newcastleinfotech dot com dot au
6 years ago
Also note that any data in the buffer will flush at the end of the script, not destroyed, so it is often not necessary to call ob_flush(); for example:

<?php
ob_start
();
echo
'Hello World!'
?>

Will still result in Hello World! being displayed to the browser.
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