ob_start

(PHP 4, PHP 5, PHP 7, PHP 8)

ob_start打开输出控制缓冲

说明

ob_start ( callable $output_callback = null , int $chunk_size = 0 , int $flags = PHP_OUTPUT_HANDLER_STDFLAGS ) : bool

此函数将打开输出缓冲。当输出缓冲激活后,脚本将不会输出内容(除http标头外),相反需要输出的内容被存储在内部缓冲区中。

内部缓冲区的内容可以用 ob_get_contents() 函数复制到一个字符串变量中。 想要输出存储在内部缓冲区中的内容,可以使用 ob_end_flush() 函数。另外, 使用 ob_end_clean() 函数会静默丢弃掉缓冲区的内容。

Warning

当有正在调用的回调函数时,一些网络服务器(例如Apache)会改变一个脚本的工作目录。 你可以在回调函数中再把它改回来,例如 chdir(dirname($_SERVER['SCRIPT_FILENAME']))

输出缓冲区是可堆叠的,这即意谓着,当有一个 ob_start() 是活跃的时, 你可以调用另一个 ob_start() 。 只要确保又正确调用了 ob_end_flush() 恰当的次数即可。 如果有多重输出回调函数是活跃的,输出内容会一直按嵌套的顺序依次通过它们而被过滤。

参数

output_callback

可选参数 output_callback 函数可以被指定。 此函数把一个字符串当作参数并返回一个字符串。 当输出缓冲区被( ob_flush(), ob_clean() 或者相似的函数)冲刷(送出)或者被清洗的时候;或者在请求结束之际输出缓冲区内容被冲刷到浏览器的时候该函数将会被调用。 当调用 output_callback 时,它将收到输出缓冲区的内容作为参数 并预期返回一个新的输出缓冲区作为结果,这个新返回的输出缓冲区内容将被送到浏览器。 如果这个 output_callback 不是一个可以调用的函数,此函数 会返回 false。以下是回调签名:

handler ( string $buffer , int $phase = ? ) : string
buffer
输出缓冲区中的内容。
phase
比特掩码 PHP_OUTPUT_HANDLER_* 常量

如果 output_callback 返回 false ,其原来的输入 内容被直接送到浏览器。

这个参数 output_callback 可以通过直接给一个 null 值而避开。

ob_end_clean(), ob_end_flush(), ob_clean(), ob_flush()ob_start() 不能从一个回调函数中调用。 如果从回调函数中调用了它们,产生的行为是不明确的。 如果想要删除缓冲区的内容,从回调函数中返回一个"" (空字符串)。 更不能从一个回调函数中使用像print_r($expression, true)highlight_file($filename, true) 一样的输出缓冲函数。

Note:

ob_gzhandler() function exists to facilitate sending gz-encoded data to web browsers that support compressed web pages. ob_gzhandler() determines what type of content encoding the browser will accept and will return its output accordingly.

chunk_size

如果可选参数 chunk_size 被赋值了,在任何一个能引起缓冲区的长度等于 或超过 chunk_size 的输出操作后,缓冲区都会被刷送。 默认值 0 意味着函数仅在最后被调用。

PHP 5.4.0 之前,1 是一个特殊情况下的值,代表将 chunk_size 设置为 4096 字节。

flags

flags 参数代表了一个掩码位,用来控制对缓冲区的操作。 The default is to allow output buffers to be cleaned, flushed and removed, which can be set explicitly via PHP_OUTPUT_HANDLER_CLEANABLE | PHP_OUTPUT_HANDLER_FLUSHABLE | PHP_OUTPUT_HANDLER_REMOVABLE, or PHP_OUTPUT_HANDLER_STDFLAGS as shorthand.

每个标志都控制着对一组功能的访问,详细介绍如下:

Constant Functions
PHP_OUTPUT_HANDLER_CLEANABLE ob_clean(), ob_end_clean()ob_get_clean()
PHP_OUTPUT_HANDLER_FLUSHABLE ob_end_flush(), ob_flush()ob_get_flush()
PHP_OUTPUT_HANDLER_REMOVABLE ob_end_clean(), ob_end_flush()ob_get_flush()

返回值

成功时返回 true, 或者在失败时返回 false

范例

Example #1 用户自定义回调函数的例子

<?php

function callback($buffer)
{
  
// replace all the apples with oranges
  
return (str_replace("apples""oranges"$buffer));
}

ob_start("callback");

?>
<html>
<body>
<p>It's like comparing apples to oranges.</p>
</body>
</html>
<?php

ob_end_flush
();

?>

以上例程会输出:

<html>
<body>
<p>It's like comparing oranges to oranges.</p>
</body>
</html>

Example #2 以兼容 PHP 5.3 和 5.4 的方式创建一个不可擦除的输出缓冲区

<?php

if (version_compare(PHP_VERSION'5.4.0''>=')) {
  
ob_start(null0PHP_OUTPUT_HANDLER_STDFLAGS ^
    
PHP_OUTPUT_HANDLER_REMOVABLE);
} else {
  
ob_start(null0false);
}

?>

参见

User Contributed Notes

mbutscher at gmx dot de 24-Sep-2016 12:52
In case of an error the contents of the output buffer are shown along with the error message. If it is really important that this does never happen, you can do the following (but this also eats up the error message):

<?php
$outputbufferOutput
= FALSE;

function
switchableOutputHandler($buffer) {
    global
$outputbufferOutput;

    if (
$outputbufferOutput)
        return
$buffer;
    else
        return
"";
}

function
internob_start() {
    global
$outputbufferOutput;

   
$outputbufferOutput = FALSE;
    return
ob_start("switchableOutputHandler");
}

function
internob_get_clean() {
    global
$outputbufferOutput;
   
   
$outputbufferOutput = TRUE;
   
$result = ob_get_clean();
   
$outputbufferOutput = FALSE;
    return
$result;
}

?>

You can then use internob_start() and internob_get_clean() instead of ob_start() and ob_get_clean(). Other functions can be replaced accordingly.
bty-adminf2 at trebly dot net 28-Jul-2015 05:27
This concerns the default values used for ob_start().

Note that I could verify that ob_start() and ob_start(null,0) are not always equivalent.

It seems that with ob_start() the output buffer is open with current default parameters of your configuration if they have been explicitly defined.

So, if you have set $chunk_size to any value previously and send data larger than $chunk_size the data will be automatically flushed by blocks of $chunk_size.

If you explicitely define $chunk_size=0, later, when you will use any function as $my_ob_dataoutput=ob_get_clean(); you  will get back the whole content of your output (quite unlimited with $chunk_size=0).

I discover this because my var $my_ob_dataoutput was truncated. Using "ob_get_status (true)" function, I could verify that an error (in a lower level or by default out of my control) was setting previously the $chunk_size of ob at 4096.
I changed "ob_start()" for "ob_start(null,0)" and everything became OK.
jhlavon 19-Jun-2013 12:47
When used in constructor part of class it have to be prefixed by "self::" or by classname, else PHP fails to create buffer.

function __construct ()
{

$bo = ob_start ("self::callback_ob") ;
...
}
me at haravikk dot com 19-Jun-2012 07:26
I think it's worth noting that while you can't call any output functions such as echo or print from within a callback function, you can still send headers (presumably including cookies, haven't checked). Of course this only works in the first callback, like so:

<?php

function myCallback($buffer, $flags) {
    if (
$flags & PHP_OUTPUT_HANDLER_START) {
       
header('Server: LastMinuteHeaderServer');
    }
}

ob_start('myCallback');
echo
"Hello World!";
ob_end_flush();

?>

Not the most inspiring example, but in this case the code is able to sneak a last-minute header in before the headers part of the response is sent. This can be handy if you want to avoid replacing header values that are uncertain.

For example if your code may return an image, but you don't want to set content type until you're sure that the image can be sent successfully, you can use the callback to leave the decision right until the very last moment, by which point you're hopefully sure of what's being sent in the HTTP body.
mchojrin at gmail dot com 30-May-2012 02:23
Just a word of warning to those like myself who are upgrading from 5.3. I have a piece of code that used to work:

<?php
if ( !ob_start( !DEBUGMODE ? 'ob_gzhandler' : '' ) ) {
   
ob_start();
}
?>

Which is not working anymore (I get an error like: Warning: ob_start(): function '' not found or invalid function name).

It's easily fixed though, just changed the '' to a null, like this:

<?php
if ( !ob_start( !DEBUGMODE ? 'ob_gzhandler' : null ) ) {
   
ob_start();
}       
?>

Which preserves the code intention but works :)
Filip Dalge 22-Mar-2012 12:24
When a fatal error is thrown, PHP will output the current buffer of Output-Control without postprocessing before printing the error message. If you are working with several output control levels, this might not result in the desired behavior.

You can use an output callback handler to handle this and discard the output.

Therefore, use ob_start("ob_error_handler") in connection with the following:

function ob_error_handler($str) {
    $error = error_get_last();
    if ($error && $error["type"] == E_USER_ERROR || $error["type"] == E_ERROR) {
        return ini_get("error_prepend_string").
          "\nFatal error: $error[message] in $error[file] on line $error[line]\n".
          ini_get("error_append_string");
    }
    return $str;
}
Anonymous 08-Feb-2011 07:32
In case you're in for some readable representation for flags, this is a variant as a private class member:

<?php
class foo {
    private function
getFlagsReadable($flags) {
       
$flagNames = array('PHP_OUTPUT_HANDLER_START', 'PHP_OUTPUT_HANDLER_CONT', 'PHP_OUTPUT_HANDLER_END');
       
$readable = '';
        foreach(
$flagNames as $flagName)
            if (
$flags & constant($flagName) )
               
$readable .= (strlen($readable) ? ' | ' : '') . $flagName
           
;       
        return
$readable;
    }
}
?>
Chris 24-Nov-2010 04:35
Careful with while using functions that change headers of a page; that change will not be undone when ending output buffering.

If you for instance have a class that generates an image and sets the appropriate headers, they will still be in place after the end of ob.

For instance:
<?php
  ob_start
();
 
myClass::renderPng(); //header("Content-Type: image/png"); in here
 
$pngString = ob_get_contents();
 
ob_end_clean();
?>

will put the image bytes into $pngString, and set the content type to image/png. Though the image will not be sent to the client, the png header is still in place; if you do html output here, the browser will most likely display "image error, cannot be viewed", at least firefox does.

You need to set the correct image type (text/html) manually in this case.
Bitwise 21-Oct-2009 12:41
There is no start flag problem. One just has to notice that the second parameter is not a mode but consists of bitwise-OR'ed flags.

<?php
function ob_handler($string, $flags) {
        static
$input = array();
        if (
$flags & PHP_OUTPUT_HANDLER_START )
               
$flags_sent[] = "PHP_OUTPUT_HANDLER_START";
        if (
$flags & PHP_OUTPUT_HANDLER_CONT )
               
$flags_sent[] = "PHP_OUTPUT_HANDLER_CONT";
        if (
$flags & PHP_OUTPUT_HANDLER_END )
               
$flags_sent[] = "PHP_OUTPUT_HANDLER_END";
       
$input[] = implode(' | ', $flags_sent) . " ($flags): $string<br />";
       
$output  = "$string<br />";
        if (
$flags & PHP_OUTPUT_HANDLER_END ) {
               
$output .= '<br />';
                foreach(
$input as $k => $v) $output .= "$k: $v";
        }
        return
$output;
}

ob_start('ob_handler');

echo
'flush';
ob_flush();

echo
'flush 2';
ob_flush();

echo
'clean';
ob_clean();

echo
'flush 3';
ob_flush();

echo
'end flush';
ob_end_flush();
?>

flush
flush 2
flush 3
end flush

0: PHP_OUTPUT_HANDLER_START | PHP_OUTPUT_HANDLER_CONT (3): flush
1: PHP_OUTPUT_HANDLER_CONT (2): flush 2
2: PHP_OUTPUT_HANDLER_CONT (2): clean
3: PHP_OUTPUT_HANDLER_CONT (2): flush 3
4: PHP_OUTPUT_HANDLER_END (4): end flush
clancy hood at gmail dot com 19-Sep-2009 05:31
With ob callback: note that the second parameter sent to your method won't help you differentiate between flush calls and calls to ob_clean, but the buffer contents is sent in both cases, so you end up parsing data that isn't going to be used. Also, note that the constant PHP_OUTPUT_HANDLER_START is never actually sent, rather the integer "3" turns up on first flush:
<?php

   
function ob_handler($string, $flag){
        static
$input = array();
       
$done = false;
        switch(
$flag){
            case
PHP_OUTPUT_HANDLER_START:   
               
$flag_sent = "PHP_OUTPUT_HANDLER_START ($flag)";
                break; 
            case
PHP_OUTPUT_HANDLER_CONT:
               
$flag_sent = "PHP_OUTPUT_HANDLER_CONT ($flag)";
                break;
            case
PHP_OUTPUT_HANDLER_END:
               
$done = true;
               
$flag_sent = "PHP_OUTPUT_HANDLER_END ($flag)";
                break;
            default:
               
$flag_sent = "Flag is not a constant ($flag)";
        }
       
$input[] = "$flag_sent: $string<br />";
       
$output = "$string<br />";
        if(!
$done) return $output;
       
// print_r($input, 1) causes an error and var_export just doesn't work
       
$output .= '<br />';
        foreach(
$input as $k=>$v) $output .= "$k: $v";
        return
$output;
    }

   
ob_start('ob_handler');

    echo
'flush';
   
ob_flush();

    echo
'flush 2';
   
ob_flush();

    echo
'clean';
   
ob_clean();

    echo
'flush 3';
   
ob_flush();

    echo
'end flush';
   
ob_end_flush();
?>
?
flush
flush 2
flush 3
end flush

0: Flag is not a constant (3): flush
1: PHP_OUTPUT_HANDLER_CONT (2): flush 2
2: PHP_OUTPUT_HANDLER_CONT (2): clean
3: PHP_OUTPUT_HANDLER_CONT (2): flush 3
4: PHP_OUTPUT_HANDLER_END (4): end flush

I suppose the START flag problem *may* be a bug but I'm not able to upgrade before reporting since I must have the same version as my server (I'm on PHP 5.2.6). If anyone has 5.2.11 or other stable version feel free to test/report as you see fit.
mariusads at helpedia dot com 02-Jul-2009 03:02
Make sure the editor you use does not add the UTF8/UTF16 BOM at the start of the scripts if you want to use ob_start("ob_gzhandler");

If those three characters are present, browsers like Firefox won't be able to decode the pages and will report:

Content Encoding Error

The page you are trying to view cannot be shown because it uses an invalid or unsupported form of compression.

The page you are trying to view cannot be shown because it uses an invalid or unsupported form of compression.

Google Chrome will simply report "Error 2 (net::ERR_FAILED): Unknown error."

With the ob_start command commented out, the page is successfully load and the browser will usually detect the BOM and not show it on the page, so everything's hard to debug.
cj at ceejayoz dot com 29-Dec-2008 08:45
Note that since PHP 5.1.x, all objects have their destructors called before the output buffer callback function executes. Thus, globalised objects will not be available as expected in the function.

This is stated to be intended behaviour, per http://bugs.php.net/bug.php?id=40104
codextasy at gmail dot com 19-Sep-2008 01:26
There is a difference between the documentation and real callback functions invocation.
Manual says: "The function will be called when ob_end_flush() is called, or when the output buffer is flushed to the browser at the end of the request."

Actually, the callback function, once set by ob_start(), will be called regardless.
Here are the functions that invoke callback function immediately:
ob_clean
ob_end_clean
ob_end_flush
ob_flush
ob_get_clean

BUT only two of them return the result returned by the callback (ob_end_flush, ob_flush), other functions discard it.

At the end of the request, even if none of the functions listed above is called, the callback will be called anyway, and its result will be returned to the browser (well, at least this is corresponding to the manual).

There is one more trick:
If you set callback function with chunk_size > 1, callback function will be called each time output buffer is equal or exceeds chunk_size and its result will be output to the browser, even if you call any of ob_clean(), ob_end_clean(), ob_get_clean() later, so be aware of this fact.
fordiman at gmail dot com 27-Jun-2008 09:35
Here's a nifty function I use daily.  Essentially: include a PHP file - but render its output to a variable, rather than to the buffer.  It's also set up to load the script with a variable set, and automagically loads globals into the script's namespace, making it an effective templating scheme.  It also has error handling, so that you're not flying blind when using output buffering.

<?php
$GLOBALS
['BufferedErrors']=Array();
function
errorParse($errno, $errstr, $errfile, $errline, $errcontext) {
   
$errorTypes = Array(
       
E_ERROR => 'Fatal Error',
       
E_WARNING => 'Warning',
       
E_PARSE => 'Parse Error',
       
E_NOTICE => 'Notice',
       
E_CORE_ERROR => 'Fatal Core Error',
       
E_CORE_WARNING => 'Core Warning',
       
E_COMPILE_ERROR => 'Compilation Error',
       
E_COMPILE_WARNING => 'Compilation Warning',
       
E_USER_ERROR => 'Triggered Error',
       
E_USER_WARNING => 'Triggered Warning',
       
E_USER_NOTICE => 'Triggered Notice',
       
E_STRICT => 'Deprecation Notice',
       
E_RECOVERABLE_ERROR => 'Catchable Fatal Error'
   
);
   
$ret=(object)Array(
       
'number'=>$errno,
       
'message'=>$errstr,
       
'file'=>$errfile,
       
'line'=>$errline,
       
'context'=>$errcontext,
       
'type'=>$errorTypes[$errno]
    );
   
$GLOBALS['BufferedErrors'][]=$ret;
    return
false;
}
function
parse($fileToInclude, $argumentsToFile=false) {
   
$bufferedErrorStack = $GLOBALS['BufferedErrors'];
   
set_error_handler('errorParse', error_reporting());
   
$GLOBALS['BufferedErrors']=Array();
   
    if (!
file_exists($fileToInclude))
        return
'';
    if (
$argumentsToFile === false)
       
$argumentsToFile = Array();
   
$argumentsToFile = array_merge($GLOBALS, $argumentsToFile);
    foreach (
$argumentsToFile as $variableName => $variableValue)
        $
$variableName = $variableValue;
   
ob_start();
    include(
$fileToInclude);
   
$ret = ob_get_contents();
   
ob_end_clean();
   
   
restore_error_handler();
   
$errors = $GLOBALS['BufferedErrors'];
   
$GLOBALS['BufferedErrors'] = $bufferedErrorStack;
    if (
count($errors)>0) {
       
$ret.='<ul class="error">';
        foreach (
$errors as $error)
           
$ret.=
               
'<li>'.
                   
'<b>'.$error->type.'</b>: '.
                   
$error->message.
                   
'<blockquote>'.
                       
'<i>file</i>: '.$error->file.'<br />'.
                       
'<i>line</i>: '.$error->line.
                   
'</blockquote>'.
               
'</li>';
       
$ret.='</ul>';
    }
    return
$ret;
}
coldshine at gmail dot com 07-Apr-2008 11:52
Referring to dan at roteloftet dot com's comment:

RFC 2616 (HTTP) specifies a "transparent" Content-Encoding, "identity" (§ 3.5), that nicely suits what you tried to do with the (invalid) "None". So this equally working, and it's also RFC-compliant:

<?php
header
('Content-Encoding: identity', true);
?>
dan at roteloftet dot com 09-Mar-2008 02:19
Some web hosting servers (mine do, at least) have in their php.ini the following setting:
output_handler = ob_gzhandler

This proved problematic for php-scripts which returns an image or a binary file in general, since there is no way to determine the content length of the compressed file.

Since I spent a lot of time scouring the net searching for a work-around (.htaccess-modifications were out of the picture for various reasons), I found this to work nicely to cancel out the ob_gzhandler specified in the php.ini:

<?php
while (ob_get_level())
       
ob_end_clean();
header("Content-Encoding: None", true);
?>

Put this at the top of the script before anything else is written to the page, and the script result will not be compressed.
Francois Hill 22-Oct-2007 05:42
Following clement dot ayme at st dot com 's remark :

In my experience it seems that the output IS buffered, but ALSO sent to the standard output !
Charlie Farrow 18-Oct-2007 09:49
Under certain freak conditions, when an error ocours perfoming an action on an object that cannot be done (either because the object does not exist or the method does not exist) inside of an ob_start() the script will exit and print everything the current function generates before the error, but nothing else, including no error message.

I am at a loss to why no error message appears and am trying to get a working example for the developers that is simpler than my whole program!

So if you are using ob_start() and you get no output, check your objects.... you have made a mistake on them somewhere. The only trouble is you will not know where as there is no error!!
Asher Haig (ahaig at ridiculouspower dot com) 20-Aug-2007 01:17
When a script ends, all buffered output is flushed (this is not a bug: http://bugs.php.net/bug.php?id=42334&thanks=4). What happens when the script throws an error (and thus ends) in the middle of an output buffer? The script spits out everything in the buffer before printing the error!

Here is the simplest solution I have been able to find. Put it at the beginning of the error handling function to clear all buffered data and print only the error:

$handlers = ob_list_handlers();
while ( ! empty($handlers) )    {
    ob_end_clean();
    $handlers = ob_list_handlers();
}
tracey AT archive DOT org 29-Mar-2007 01:01
Way to make all stdout and stderr write to a log
from *inside* a php script.
You simply need to make sure to call elog() every
once in awhile to get output.
It's a nice way to "daemonize" a script w.r.t. its logging.

// This allows us to capture all stdout and stderr (and error_log() calls)
// to this logfile...
// The "collected output" will be flushed anytime "elog()" is used...
ini_set("error_log", "/var/log/script.log");
ob_start();

function elog($str)
{
  // get anything written to stdout or stderr that did *NOT* use elog()
  // and write it now...
  $writeme = ob_get_contents();
  if ($writeme)
  {
    error_log($writeme);
    ob_end_clean();
    ob_start();
  }
  // now write message this method was called with
  error_log($str);
}
lucky760 at yahoo dot com 21-Nov-2006 09:10
In extension to the compress() function posted below, here's a nifty little class that improves the idea a bit. Basically, running that compress() function for all your CSS for every single page load is clearly far less than optimal, especially since the styles will change only infrequently at the very worst.

With this class you can simply specify an array of your CSS file names and call dump_style(). The contents of each file are saved in compress()'d form in a cache file that is only recreated when the corresponding source CSS changes.

It's intended for PHP5, but will work identically if you just un-OOP everything and possibly define file_put_contents.

Enjoy!

<?php

$CSS_FILES
= array(
 
'_general.css'
);

$css_cache = new CSSCache($CSS_FILES);
$css_cache->dump_style();

//
// class CSSCache
//

class CSSCache {
  private
$filenames = array();
  private
$cwd;
   
  public function
__construct($i_filename_arr) {
    if (!
is_array($i_filename_arr))
     
$i_filename_arr = array($i_filename_arr);
   
   
$this->filenames = $i_filename_arr;
   
$this->cwd = getcwd() . DIRECTORY_SEPARATOR;
   
    if (
$this->style_changed())
     
$expire = -72000;
    else
     
$expire = 3200;
   
   
header('Content-Type: text/css; charset: UTF-8');
   
header('Cache-Control: must-revalidate');
   
header('Expires: ' . gmdate('D, d M Y H:i:s', time() + $expire) . ' GMT');
  }
 
  public function
dump_style() {
   
ob_start('ob_gzhandler');
   
    foreach (
$this->filenames as $filename)
     
$this->dump_cache_contents($filename);
   
   
ob_end_flush();
  }
 
    private function
get_cache_name($filename, $wildcard = FALSE) {
   
$stat = stat($filename);
    return
$this->cwd . '.' . $filename . '.' .
      (
$wildcard ? '*' : ($stat['size'] . '-' . $stat['mtime'])) . '.cache';
  }
 
  private function
style_changed() {
    foreach (
$this->filenames as $filename)
      if (!
is_file($this->get_cache_name($filename)))
        return
TRUE;
    return
FALSE;
  }

  private function
compress($buffer) {
   
$buffer = preg_replace('!/\*[^*]*\*+([^/][^*]*\*+)*/!', '', $buffer);
   
$buffer = str_replace(array("\r\n", "\r", "\n", "\t", '  '), '', $buffer);
   
$buffer = str_replace('{ ', '{', $buffer);
   
$buffer = str_replace(' }', '}', $buffer);
   
$buffer = str_replace('; ', ';', $buffer);
   
$buffer = str_replace(', ', ',', $buffer);
   
$buffer = str_replace(' {', '{', $buffer);
   
$buffer = str_replace('} ', '}', $buffer);
   
$buffer = str_replace(': ', ':', $buffer);
   
$buffer = str_replace(' ,', ',', $buffer);
   
$buffer = str_replace(' ;', ';', $buffer);
    return
$buffer;
  }
 
  private function
dump_cache_contents($filename) {
   
$current_cache = $this->get_cache_name($filename);
   
   
// the cache exists - just dump it
   
if (is_file($current_cache)) {
      include(
$current_cache);
      return;
    }
   
   
// remove any old, lingering caches for this file
   
if ($dead_files = glob($this->get_cache_name($filename, TRUE), GLOB_NOESCAPE))
      foreach (
$dead_files as $dead_file)
       
unlink($dead_file);
   
   
$compressed = $this->compress(file_get_contents($filename));
   
file_put_contents($current_cache, $compressed);
   
    echo
$compressed;
  }
}

?>
butch at enterpol dot pl 02-Oct-2006 12:04
simple code to make phpsession $_GET nice for Valid XHTML 1.0 Transitional :)

function callback($buffer)
{
  $buffer = str_replace("&PHPSESSID", "&amp;PHPSESSID", $buffer);
  return $buffer;
}

ob_start("callback");

session_start();
net_navard at yahoo dot com 30-May-2006 07:09
Hello firends

ob_start() opens a buffer in which all output is stored. So every time you do an echo, the output of that is added to the buffer. When the script finishes running, or you call ob_flush(), that stored output is sent to the browser (and gzipped first if you use ob_gzhandler, which means it downloads faster).

The most common reason to use ob_start is as a way to collect data that would otherwise be sent to the browser.

These are two usages of ob_start():

1-Well, you have more control over the output. Trivial example: say you want to show the user an error message, but the script has already sent some HTML to the browser. It'll look ugly, with a half-rendered page and then an error message. Using the output buffering functions, you can simply delete the buffer and sebuffer and send only the error message, which means it looks all nice and neat buffer and send
2-The reason output buffering was invented was to create a seamless transfer, from: php engine -> apache -> operating system -> web user

If you make sure each of those use the same buffer size, the system will use less writes, use less system resources and be able to handle more traffic.

With Regards, Hossein
simon 24-Jan-2006 08:51
Found that variables in class instances we're not being set after the call to ob_start().
Call ob_start after the variables are set however and it works but that didn't seem to solve the goal of a self contained templating class.
The fix was to assign the class by reference with '&new'
Here is a simplified working example:
<?php
class Buffer {
var
$template = ' - template set in class constructor';
function
Buffer() {
   
$this->startBuffer();
}
function
startBuffer() {
   
ob_start(array(&$this, 'doFlush'));
}
function
doFlush($buffer) {
   
/* simple string concat to show use of a
    template string and the buffer output */
   
return $buffer . $this->template;
}
}
/* template does not get set:
$buffer1 = new Buffer();
$buffer1->template = ' - template set in instance';
echo 'some buffer content';
*/
/* this works as expected */
$buffer2 = &new Buffer();
$buffer2->template = ' - template set in instance';
echo
'some buffer content';
ernest at vogelsinger dot at 08-Jan-2006 09:57
When you rely on URL rewriting to pass the PHP session ID you should be careful with ob_get_contents(), as this might disable URL rewriting completely.

Example:
ob_start();
session_start();
echo '<a href=".">self link</a>';
$data = ob_get_contents();
ob_end_clean();
echo $data;

In the example above, URL rewriting will never occur. In fact, rewriting would occur if you ended the buffering envelope using ob_end_flush(). It seems to me that rewriting occurs in the very same buffering envelope where the session gets started, not at the final output stage.

If you need a scenario like the one above, using an "inner envelope" will help:

ob_start();
ob_start();   // add the inner buffering envelope
session_start();
echo '<a href=".">self link</a>';
ob_end_flush(); // closing the inner envelope will activate URL rewriting
$data = ob_get_contents();
ob_end_clean();
echo $data;

In case you're interested or believe like me that this is rather a design flaw instead of a feature, please visit bug #35933 (http://bugs.php.net/bug.php?id=35933) and comment on it.
admin at bobfrank dot org 28-Aug-2005 08:50
If you want to run code in the middle of a string that you made, but you want to wait the printing...
(so if you want to allow php in bb-code style, and you want to execute it in order, and print everything in order...)

phpRun($code) {
    ob_start();
    exec($code);
    $output = ob_get_contents();
    ob_end_clean();
    return $output;
}

$str = str_replace("]\n", "]", $str);
$match = array('#\[php\](.*?)\[\/php\]#se');
$replace = array( phpRun( stripslashes('$1') ) );
$str= preg_replace($match, $replace, $str);

echo $str;
geoffrey at nevra dot net 09-Aug-2005 12:05
When using a callback with ob_start(), functions like ob_get_contents() don't make use of it, use ob_end_flush() instead.

nb: not tested with every ob_* functions, just ob_get_contents() and ob_end_flush()
05-Aug-2005 07:54
I usually create my pages in four parts - variable initialisation, import header (using the variables just declared to configure), main body (mostly non-PHP), import footer.  I wondered about making the main body examinable by another PHP script if the main page was included into it.  I found I could control output of the main body by ending the header with an unclosed function which finishes at the start of the footer, thus enclosing the main body.  Output buffering can then be used to read this into a variable.  As a demonstration of how this can be used to control the order of output look at this example:

<?php
$output
= "";

// Callback to process buffered output
function capture($buffer)
    {
   
$GLOBALS['output'] .= $buffer;
    return
"C ";
    }

// Calls the printE() function with output capture
function captureE()
    {
   
ob_start("capture");
   
printE();
   
ob_end_flush();
    }
?>

A
<?php
// Output 'E' (the main body in the example scenario)
function printE()
    {
// (End header after this line) ?>
E
    <?php // (Start footer with this line)
   
}
?>
B
<?php captureE(); ?>
D
<?php print $output; ?>
F
<?php printE(); ?>
G

The output is A B C D E F E G.

For the application I mentioned above there are two points to note:
 - The page when executed alone must output its main body but the inspection script should suppress this, perhaps by means of a variable set before the page is included and then checked for in the footer output lines.
 - Because the main body is now inside a function it has a different namespace, thus changes may be required to prevent code breaking (e.g. use of globals, handling of functions defined within the main body).
oersoep at gmail dot com 08-Jul-2005 05:46
These are handy. First one has been mentioned before.

ob_start( array( 'lib_class', 'parse_output' ) );
ob_start( array( $this, 'parse_output' ) );

Note: $this is NOT a reference. Anything the callback saves or logs disappears in the clone ob_start works with.
It does enable the callback to work with the attributes of $this, like $this->ar_tpl_value or whatever your style is.

The manual says:
"If the optional parameter chunk_size is passed, the callback function is called on every first newline after chunk_size bytes of output. The output_callback parameter may be bypassed by passing a NULL value."
This doesn't work with my 4.3.11. Might be the Zend optimizer though. Daren't turn it off to go see.
Aleksey 25-May-2005 12:08
This function dynamically changes title of HTML page:

  function change_title($new_title) {
    $output = ob_get_contents();
    ob_end_clean();

    $output = preg_replace("/<title>(.*?)<\/title>/", "<title>$new_title</title>", $output);
    echo $output;
  }

Example:
  ob_start();
  // ... some output
  change_title('NEW TITLE!');
rafa dot chacon at factorydea dot com 10-May-2005 02:10
If you're trying to include a php file inside a loop by require_once (in example, a dinamic email template) and change the value of some variables (in example, url to unsuscribe, different for each user), you should use

<?php

// ... some code

$usermail = array("email1", "email2", ...);

for(
$i = 0; $i < $MAX; $i++)
{
       
$usermail_unsuscribe = $usermail[$i];
       
ob_start();
        include(
"email_template.php");
       
ob_clean();
}
?>

Otherwise $usermail_unsuscribe will get only "email1" value.
Ray Paseur (Paseur ... ImagineDB.com) 01-Mar-2005 01:50
You can use PHP to generate a static HTML page.  Useful if you have a complex script that, for performance reasons, you do not want site visitors to run repeatedly on demand.  A "cron" job can execute the PHP script to create the HTML page.  For example:

<?php // CREATE index.html
  
ob_start();
/* PERFORM COMLEX QUERY, ECHO RESULTS, ETC. */
  
$page = ob_get_contents();
  
ob_end_clean();
  
$cwd = getcwd();
  
$file = "$cwd" .'/'. "index.html";
   @
chmod($file,0755);
  
$fw = fopen($file, "w");
  
fputs($fw,$page, strlen($page));
  
fclose($fw);
   die();
?>
aaron at offtone.com 13-Nov-2004 05:19
My callback is stored in a function class, and using ob_start ('Class::callback') wasn't working. Not wanting to instantiate the class (no need, it's a function class) I tried this and it worked a charm:

ob_start (array (Class, 'callback'));

PHP 4.3.4
jkloss at hotmail dot com 17-Mar-2004 07:20
If ob_start does not seem to be working for you, note that with Apache 2 the flush() function causes PHP to send headers regardless of whether ob_start had been called before flush.

ob_start();
echo 'test';
flush();

will cause Apache 2 to send whatever headers may be stacked up - which means you can't use a header(location:xxx) after the flush.  To fix, remove the flush().  Spent several hours discovering this.  Apache 1.x didn't work this way.
mjr 10-Mar-2004 09:10
If you're using object-orientated code in PHP you may, like me, want to use a call-back function that is inside an object (i.e. a class function). In this case you send ob_start a two-element array as its single argument. The first element is the name of the object (without the $ at the start), and the second is the function to call. So to use a function 'indent' in an object called '$template' you would use <?php ob_start(array('template', 'indent')); ?>.
ed.oohay (a) suamhcs_rodnan 21-Nov-2003 05:18
Output Buffering even works in nested scopes or might be applied in recursive structures... thought this might save someone a little time guessing and testing :)

<pre><?php
   
    ob_start
();              // start output buffer 1
   
echo "a";                // fill ob1
       
       
ob_start();              // start output buffer 2
       
echo "b";                // fill ob2
       
$s1 = ob_get_contents(); // read ob2 ("b")
       
ob_end_flush();          // flush ob2 to ob1
       
   
echo "c";                // continue filling ob1
   
$s2 = ob_get_contents(); // read ob1 ("a" . "b" . "c")
   
ob_end_flush();          // flush ob1 to browser
   
    // echoes "b" followed by "abc", as supposed to:
   
echo "<HR>$s1<HR>$s2<HR>";
   
?></pre>

... at least works on Apache 1.3.28

Nandor =)
05-Dec-2002 12:02
If you're using Apache (1.3x or 2.0), you might consider adding automatic compression capability to your delivered pages.

I assume you all know how to build compression classes and use them in your programs, but none has yet to offer the speed and robustness of a binary-compiled module. Furthermore, such modules also log the "compressable" hit in the web log file, thus allowing your favorite web anaysing program to show you reports of bandwidth saved.

Having said that, you might consider the following two modules for Apache:

1) Apache 1.3x: use mod_gzip, available from:
http://sourceforge.net/projects/mod-gzip/

2) Apache 2.x: use mod_gz, see here:
http://www.mail-archive.com/[email protected]/msg00734.html

3) Apache 1.3x: you may also want to use mod_defalte, from:
ftp://ftp.lexa.ru/pub/apache-rus/contrib/

Hope it helps.
cliff at NOSPAMtravelguides dot com 07-Aug-2002 03:36
good article on output buffering on devshed:

http://www.devshed.com/c/a/PHP/Output-Buffering-With-PHP