(PHP 4, PHP 5, PHP 7, PHP 8)
ob_start — Turn on output buffering
$callback = null, int$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, instead the output is stored in an internal buffer. See What Output Is Buffered? on exactly what output is affected.
Output buffers are stackable, that is, ob_start() may be called while another buffer is active. If multiple output buffers are active, output is being filtered sequentially through each of them in nesting order. See Nesting Output Buffers for more details.
See User-Level Output Buffers for a detailed description of output buffers.
callback An optional callbackcallable may be specified. It can also be bypassed by passing null.
callback is invoked when the output buffer is flushed (sent), cleaned, or when the output buffer is flushed at the end of the script.
The signature of the callback is as follows:
bufferphasePHP_OUTPUT_HANDLER_* constants . See Flags Passed To Output Handlers for more details. If callback returns false the contents of the buffer are returned. See Output Handler Return Values for more details.
Calling any of the following functions from within an output handler will result in a fatal error: ob_clean(), ob_end_clean(), ob_end_flush(), ob_flush(), ob_get_clean(), ob_get_flush(), ob_start().
See Output Handlers and Working With Output Handlers for more details on callbacks (output handlers).
chunk_size If the optional parameter chunk_size is passed, the buffer will be flushed after any block of code resulting in output that causes the buffer's length to equal or exceed chunk_size. The default value 0 means that all output is buffered until the buffer is turned off. See Buffer Size for more details.
flags The flags parameter 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 via the buffer control flags . See Operations Allowed On Buffers for more details.
Each flag controls access to a set of functions, as described below:
| Constant | Functions |
|---|---|
PHP_OUTPUT_HANDLER_CLEANABLE | ob_clean() |
PHP_OUTPUT_HANDLER_FLUSHABLE | ob_end_flush() |
PHP_OUTPUT_HANDLER_REMOVABLE | ob_end_clean(), ob_end_flush(), ob_get_clean(), ob_get_flush() |
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);
?>