LXXVIII. Output Control Functions


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.


No external libraries are needed to build this extension.


There is no installation needed to use these functions; they are part of the PHP core.

Runtime Configuration

The behaviour of these functions is affected by settings in php.ini.

Table 1. Output Control configuration options

For further details and definition of the PHP_INI_* constants see ini_set().

Here's a short explanation of the configuration directives.

output_buffering boolean/integer

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).

output_handler string

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.

Note: You cannot use both mb_output_handler() with ob_inconv_handler() and you cannot use both ob_gzhandler() and zlib.output_compression.

implicit_flush boolean

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.

See also ob_implicit_flush().

Resource Types

This extension has no resource types defined.

Predefined Constants

This extension has no constants defined.


Example 1. Output Control example



setcookie("cookiename", "cookiedata");



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.)

Note: When upgrading from PHP 4.1 (and 4.2) to 4.3 that 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.

See Also

See also header() and setcookie().

Table of Contents
flush -- Flush the output buffer
ob_clean --  Clean (erase) 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_flush --  Flush (send) the output buffer
ob_get_clean --  Get current buffer contents and delete current output buffer
ob_get_contents --  Return the contents of the output buffer
ob_get_flush --  Flush the output buffer, return it as a string and turn off output buffering
ob_get_length --  Return the length of the output buffer
ob_get_level --  Return the nesting level of the output buffering mechanism
ob_get_status --  Get status of output buffers
ob_gzhandler --  ob_start callback function to gzip output buffer
ob_implicit_flush --  Turn implicit flush on/off
ob_list_handlers --  List all output handlers in use
ob_start -- Turn on output buffering
output_add_rewrite_var --  Add URL rewriter values
output_reset_rewrite_vars --  Reset URL rewriter values