ob_start
(PHP 4, PHP 5, PHP 7, PHP 8)
ob_start — Turn on output buffering
Description
$callback = null, int $chunk_size = 0, int $flags = PHP_OUTPUT_HANDLER_STDFLAGS): boolThis function will turn output buffering on. While output buffering is active no output is sent from the script (other than headers), instead the output is stored in an internal buffer.
The contents of this internal buffer may be copied into a string variable using ob_get_contents(). To output what is stored in the internal buffer, use ob_end_flush(). Alternatively, ob_end_clean() will silently discard the buffer contents.
Some web servers (e.g. Apache) change the working directory of a script
when calling the callback function. You can change it back by e.g.
chdir(dirname($_SERVER['SCRIPT_FILENAME'])) in the
callback function.
Output buffers are stackable, that is, you may call ob_start() while another ob_start() is active. Just make sure that you call ob_end_flush() the appropriate number of times. If multiple output callback functions are active, output is being filtered sequentially through each of them in nesting order.
If output buffering is still active when the script ends, PHP outputs the contents automatically.
Parameters
-
callback -
An optional
callbackfunction may be specified. This function takes a string as a parameter and should return a string. The function will be called when the output buffer is flushed (sent) or cleaned (with ob_flush(), ob_clean() or similar function) or when the output buffer is flushed to the browser at the end of the request. Whencallbackis called, it will receive the contents of the output buffer as its parameter and is expected to return a new output buffer as a result, which will be sent to the browser. If thecallbackis not a callable function, this function will returnfalse. This is the callback signature:handler(string$buffer, int$phase= ?): string-
buffer - Contents of the output buffer.
-
phase -
Bitmask of
PHP_OUTPUT_HANDLER_*constants.
If
callbackreturnsfalseoriginal input is sent to the browser.The
callbackparameter may be bypassed by passing anullvalue.ob_end_clean(), ob_end_flush(), ob_clean(), ob_flush() and ob_start() may not be called from a callback function. If you call them from callback function, the behavior is undefined. If you would like to delete the contents of a buffer, return "" (a null string) from callback function. You can't even call functions using the output buffering functions like
print_r($expression, true)orhighlight_file($filename, true)from a callback function.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 -
If the optional parameter
chunk_sizeis passed, the buffer will be flushed after any output call which causes the buffer's length to equal or exceedchunk_size. The default value0means that the output function will only be called when the output buffer is closed. -
flags -
The
flagsparameter is a bitmask that controls the operations that can be performed on the output buffer. The default is to allow output buffers to be cleaned, flushed and removed, which can be set explicitly viaPHP_OUTPUT_HANDLER_CLEANABLE|PHP_OUTPUT_HANDLER_FLUSHABLE|PHP_OUTPUT_HANDLER_REMOVABLE, orPHP_OUTPUT_HANDLER_STDFLAGSas shorthand.Each flag controls access to a set of functions, as described below:
Constant Functions PHP_OUTPUT_HANDLER_CLEANABLEob_clean(), ob_end_clean(), and ob_get_clean(). PHP_OUTPUT_HANDLER_FLUSHABLEob_end_flush(), ob_flush(), and ob_get_flush(). PHP_OUTPUT_HANDLER_REMOVABLEob_end_clean(), ob_end_flush(), and ob_get_flush().
Return Values
Returns true on success or false on failure.
Examples
Example #1 User defined callback function example
<?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();
?>
The above example will output:
<html> <body> <p>It's like comparing oranges to oranges.</p> </body> </html>
Example #2 Creating an unerasable output buffer
<?php
ob_start(null, 0, PHP_OUTPUT_HANDLER_STDFLAGS ^ PHP_OUTPUT_HANDLER_REMOVABLE);
?>
See Also
- ob_get_contents() - Return the contents of the output buffer
- ob_end_clean() - Clean (erase) the output buffer and turn off output buffering
- ob_end_flush() - Flush (send) the output buffer and turn off output buffering
- ob_implicit_flush() - Turn implicit flush on/off
- ob_gzhandler() - ob_start callback function to gzip output buffer
- ob_iconv_handler() - Convert character encoding as output buffer handler
- mb_output_handler() - Callback function converts character encoding in output buffer
- ob_tidyhandler() - ob_start callback function to repair the buffer
