ob_start

(PHP 4, PHP 5, PHP 7, PHP 8)

ob_start — Turn on output buffering

Description

ob_start(?callable $callback = null, int $chunk_size = 0, int $flags = PHP_OUTPUT_HANDLER_STDFLAGS): bool

This 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.

Parameters

callback

An optional callback callable 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:

handler(string $buffer, int $phase = ?): string
buffer
Contents of the output buffer.
phase
Bitmask of PHP_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.

Warning

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_flush()
PHP_OUTPUT_HANDLER_REMOVABLE ob_end_clean(), ob_end_flush(), ob_get_clean(), ob_get_flush()

Note: Prior to PHP 8.4.0, the flags parameter could set the output handler status flags as well.

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