ob_flush

    (PHP 4 >= 4.2.0, PHP 5, PHP 7, PHP 8)

    ob_flush — Flush (send) the return value of the active output handler

    Description

    ob_flush(): bool

    This function calls the output handler (with the PHP_OUTPUT_HANDLER_FLUSH flag), flushes (sends) its return value and discards the contents of the active output buffer.

    This function does not turn off the active output buffer like ob_end_flush() or ob_get_flush() does.

    ob_flush() will fail without an active output buffer started with the PHP_OUTPUT_HANDLER_FLUSHABLE flag.

    Parameters

    This function has no parameters.

    Return Values

    Returns true on success or false on failure.

    Errors/Exceptions

    If the function fails it generates an E_NOTICE.

    See Also

    • ob_start() - Turn on output buffering
    • ob_get_contents() - Return the contents of the output buffer
    • ob_end_flush() - Flush (send) the return value of the active output handler and turn the active output buffer off
    • ob_get_flush() - Flush (send) the return value of the active output handler, return the contents of the active output buffer and turn it off
    • ob_clean() - Clean (erase) the contents of the active output buffer

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    User Contributed Notes 11 notes

    up
    45
    Lee
    12 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.
    up
    39
    dermeister dot online at gmail dot com
    12 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 />';
    ?>
    up
    4
    thecichos at gmail dot com
    9 months ago
    The output buffer seems to work best when the server is returning a code 206 and setting the output_buffering lower temporarily to let it fill up

    This tells the browser to wait for additional content
    for example:
    // Set the header to 206
    header("HTTP/1.1 206 Partial Content; Content-Type: text/html; charset=utf-8");

    // Flush the current outputbuffer
    flush();
    ob_flush();
    ob_end_flush();

    // Create a new output buffer
    ob_start();

    // Save the current output buffer size
    $tempBuffering = ini_get("output_buffering");

    // Set a new, much smaller buffer size
    ini_set("output_buffering", 256);

    // Do some buffering
    !!! All your amazing code goes here !!!

    // Fill the buffer with something if needed
    echo str_pad(" ", (int)ini_get("output_buffering"), " ");
    flush();
    ob_flush();

    // Revert the buffer size
    ini_set("output_buffering", $tempBuffering);
    up
    11
    chris - latko - org
    9 years ago
    Although browsers now have an all or none buffering strategy, the arguments are not moot.

    If you are not using ob_flush, you run this risk of exceeding socket timeouts (commonly seen in php-fpm/nginx combos).

    Basically, flushing solves the infamous 504 Gateway Time-out error.
    up
    5
    Jens
    15 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.
    up
    2
    jake at qzdesign dot co dot uk
    5 years ago
    If there is no active output buffer, an error of level E_NOTICE is generated (at least in PHP 7.1). To avoid this, test first with `ob_get_level()`.
    up
    3
    riimeik
    13 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());
    up
    -1
    Anonymous
    18 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.
    up
    -2
    colnector at@ colnect punto com
    16 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>
    up
    -5
    sebastian at jcompare dot com
    15 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
    up
    -5
    Reynard Hilman
    19 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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