(PHP 4 >= 4.2.0, PHP 5)
ob_flush — 冲刷出（送出）输出缓冲区中的内容
这个函数将送出缓冲区的内容（如果里边有内容的话）。如果想进一步处理缓冲区中的内容，必须在 ob_flush()之前调用 ob_get_contents() ，因为在调用 ob_flush()之后缓冲区内容将被丢弃。
此函数不会销毁输出缓冲区，而像 ob_end_flush() 函数会销毁缓冲区。
没有返回值。
cesoid at gmail dot com (2013-03-08 20:30:00)
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.
Lee (2012-08-11 11:23:56)
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.
dermeister dot online at gmail dot com (2012-07-05 13:43:35)
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 $i . '<br />';
flush();
ob_flush();
sleep(1);
}
echo 'End ...<br />';
?>
riimeik (2010-10-17 13:44:34)
If you're still not getting the buffer work correctly then try to clean all the others before starting your own (and even if PHP tells you that there are no buffers active):
while(@ob_end_clean());
sebastian at jcompare dot com (2009-04-26 19:05:14)
For some reason, calling just flush or ob_flush or even both together did not get my output buffers flushed, and calling ob_end_flush by itself didn't work either but calling them all worked well. Here is my new output flushing function.
<?php
function flush_buffers(){
ob_end_flush();
ob_flush();
flush();
ob_start();
}
?>
Enjoy
Jens (2008-10-29 19:01:39)
If you call ob_flush() and flush() and still dont get the buffer flushed it might be because some antivirus software (Panda in this case) holds the buffer until the page has finished loaded before sending it to the browser.
Lucas (2008-08-27 15:13:27)
I just had some problems with flush() and ob_flush(). What I did to resolve this problem took me some time to figure out so I'd like to share what I came up with.
The main problem is the php setting "output_buffering" which can be set too large and will prevent your text from outputting. To change this value you can either set it in php.ini or you can add the line
php_value output_buffering "0"
to your .htaccess file. It will not work with ini_set() since it is PHP_INI_PERDIR.
Next thing is to begin with ob_start();
Then you need
ob_flush();
flush();
before any echo or print.
Your code might look like this:
<?php
ob_start();
for($i=0;$i<70;$i++)
{
echo 'printing...<br />';
ob_flush();
flush();
usleep(300000);
}
?>
Hope this helps anyone with the same problems.
colnector at@ colnect punto com (2008-07-08 04:35:18)
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>
kel at no-spam dot newcastleinfotech dot com dot au (2008-06-05 21:33:47)
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.
matt at ihaventthefoggiest dot com (2008-05-22 12:25:15)
Just to note, I don't think image output functions (imagejpeg, imagegif etc) are caught by ob. This code:
<?php
ob_start();
$im = imagecreateturecolor(100,20);
$white = imagecolorallocate($error_im,255,255,255);
$black = imagecolorallocate($error_im,0,0,0);
imagefttext($im,12,0,0,0,$black,'font.ttf','Hello, world!');
imagegif($im);
ob_flush();
?>
will still produce a black on white image saying "Hello, world!"
solidli at gmail dot com (2007-05-23 09:28:02)
Use an '@' sign as "@ob_flush();" to avoid the following message:
Notice: ob_flush(): failed to flush buffer. No buffer to flush. in /etc/www/test.php on line 88
(2005-09-21 18:37:19)
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.
(2005-06-24 06:27:19)
You must call them in the correct order.
ob_flush();
flush();
Reynard Hilman (2005-06-22 14:29:43)
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.
jeremy at e2-media dot co dot nz (2005-05-25 16:09:30)
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!
(2003-01-14 08:23:43)
As far as I can tell the only way to mimic ob_flush()'s behaviour on PHP < 4.2.0 is calling ob_end_flush() followed by ob_start().