The Output Control functions allow you to control when output is
sent from the script. This can be useful in several different
situations, especially if you need to send headers to the browser
after your script has began outputting data. The Output Control
functions do not affect headers sent using
header() or setcookie(),
only functions such as echo() and data between
blocks of PHP code.
When upgrading from PHP 4.1.x (and 4.2.x) to 4.3.x due to a bug in
earlier versions you must ensure that
implict_flush is OFF in
your php.ini, otherwise any output with
ob_start() will not be hidden from output.
You can enable output buffering for all files by setting this directive
to 'On'. If you wish to limit the size of the buffer to a certain size -
you can use a maximum number of bytes instead of 'On', as a value for
this directive (e.g., output_buffering=4096).
As of PHP 4.3.5, this directive is always Off in PHP-CLI.
You can redirect all of the output of your scripts to a function. For
example, if you set output_handler to
mb_output_handler(), character encoding will be
transparently converted to the specified encoding. Setting any output
handler automatically turns on output buffering.
FALSE by default. Changing this to TRUE tells PHP to tell the
output layer to flush itself automatically after every output block.
This is equivalent to calling the PHP function
flush() after each and every call to
print() or echo() and each and
every HTML block.
When using PHP within an web environment, turning
this option on has serious performance implications and is generally
recommended for debugging purposes only. This value defaults to
TRUE when operating under the CLI SAPI.
In the above example, the output from echo()
would be stored in the output buffer until
ob_end_flush() was called. In the mean time,
the call to setcookie() successfully stored a
cookie without causing an error. (You can not normally send
headers to the browser after data has already been sent.)