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
php.ini, otherwise any output with
ob_start() will not be hidden from output.
The behaviour of these functions is affected by settings in
|output_handler||NULL||PHP_INI_PERDIR||Available since PHP 4.0.4.|
|implicit_flush||"0"||PHP_INI_ALL||PHP_INI_PERDIR in PHP <= 4.2.3.|
For further details and definitions of the PHP_INI_* constants, see the Appendix I,
Here's a short explanation of the configuration directives.
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.
Only built-in functions can be used with this directive. For user defined functions, use ob_start().
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
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
See also ob_implicit_flush().
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.)
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