Turn on output buffering (original) (raw)
ob_start
(PHP 4, PHP 5, PHP 7)
ob_start — Turn on output buffering
Description
ob_start ([ callable $output_callback = NULL [, int $chunk_size = 0 [, int $flags = PHP_OUTPUT_HANDLER_STDFLAGS ]]] ) : bool
The contents of this internal buffer may be copied into a string variable using ob_get_contents(). To output what is stored in the internal buffer, use ob_end_flush(). Alternatively,ob_end_clean() will silently discard the buffer contents.
Warning
Some web servers (e.g. Apache) change the working directory of a script when calling the callback function. You can change it back by e.g.chdir(dirname($_SERVER['SCRIPT_FILENAME'])) in the callback function.
Output buffers are stackable, that is, you may callob_start() while anotherob_start() is active. Just make sure that you call ob_end_flush() the appropriate number of times. If multiple output callback functions are active, output is being filtered sequentially through each of them in nesting order.
Parameters
output_callback
An optional output_callback function may be specified. This function takes a string as a parameter and should return a string. The function will be called when the output buffer is flushed (sent) or cleaned (withob_flush(), ob_clean() or similar function) or when the output buffer is flushed to the browser at the end of the request. Whenoutput_callback is called, it will receive the contents of the output buffer as its parameter and is expected to return a new output buffer as a result, which will be sent to the browser. If the output_callback is not a callable function, this function will return FALSE. This is the callback signature:
handler ( string $buffer [, int $phase ] ) : string
buffer
Contents of the output buffer.
phase
Bitmask of PHP_OUTPUT_HANDLER_* constants.
If output_callback returns FALSE original input is sent to the browser.
The output_callback parameter may be bypassed by passing a NULL value.
ob_end_clean(), ob_end_flush(),ob_clean(), ob_flush() andob_start() may not be called from a callback function. If you call them from callback function, the behavior is undefined. If you would like to delete the contents of a buffer, return "" (a null string) from callback function. You can't even call functions using the output buffering functions likeprint_r($expression, true) orhighlight_file($filename, true) from a callback function.
Note:
ob_gzhandler() function exists to facilitate sending gz-encoded data to web browsers that support compressed web pages. ob_gzhandler() determines what type of content encoding the browser will accept and will return its output accordingly.
chunk_size
If the optional parameter chunk_size is passed, the buffer will be flushed after any output call which causes the buffer's length to equal or exceed chunk_size. The default value 0 means that the output function will only be called when the output buffer is closed.
Prior to PHP 5.4.0, the value 1 was a special case value that set the chunk size to 4096 bytes.
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**PHP_OUTPUT_HANDLER_CLEANABLE** |PHP_OUTPUT_HANDLER_FLUSHABLE |PHP_OUTPUT_HANDLER_REMOVABLE, or**PHP_OUTPUT_HANDLER_STDFLAGS** as shorthand.
Each flag controls access to a set of functions, as described below:
| Constant | Functions |
|---|---|
| PHP_OUTPUT_HANDLER_CLEANABLE | ob_clean(),ob_end_clean(), andob_get_clean(). |
| PHP_OUTPUT_HANDLER_FLUSHABLE | ob_end_flush(),ob_flush(), andob_get_flush(). |
| PHP_OUTPUT_HANDLER_REMOVABLE | ob_end_clean(),ob_end_flush(), andob_get_flush(). |
Return Values
Returns TRUE on success or FALSE on failure.
Changelog
| Version | Description |
|---|---|
| 7.0.0 | In case ob_start() is used inside an output buffer callback, this function will no longer issue an E_ERROR but instead an E_RECOVERABLE_ERROR, allowing custom error handlers to catch such errors. |
| 5.4.0 | The third parameter of ob_start() changed from aboolean parameter called erase (which, if set to FALSE, would prevent the output buffer from being deleted until the script finished executing) to aninteger parameter called flags. Unfortunately, this results in an API compatibility break for code written prior to PHP 5.4.0 that uses the third parameter. Seethe flags example for an example of how to handle this with code that needs to be compatible with both. |
| 5.4.0 | A chunk size of 1 now results in chunks of 1 byte being sent to the output buffer. |
Examples
Example #1 User defined callback function example
`
It's like comparing apples to oranges.
ob_end_flush();?> `
The above example will output:
It's like comparing oranges to oranges.
Example #2 Creating an uneraseable output buffer in a way compatible with both PHP 5.3 and 5.4
<?phpif (version_compare(PHP_VERSION, '5.4.0', '>=')) { ob_start(null, 0, PHP_OUTPUT_HANDLER_STDFLAGS ^ PHP_OUTPUT_HANDLER_REMOVABLE); } else { ob_start(null, 0, false); }?>
See Also
- ob_get_contents() - Return the contents of 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_implicit_flush() - Turn implicit flush on/off
- ob_gzhandler() - ob_start callback function to gzip output buffer
- ob_iconv_handler() - Convert character encoding as output buffer handler
- mb_output_handler() - Callback function converts character encoding in output buffer
- ob_tidyhandler() - ob_start callback function to repair the buffer