ob_startTurn on output buffering
&reftitle.description;
boolob_startcallableoutput_callback&null;intchunk_size0intflagsPHP_OUTPUT_HANDLER_STDFLAGS
This function will turn output buffering on. While output buffering is
active no output is sent from the script (other than headers), instead the
output is stored in an internal buffer.
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.
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($_SERVER['SCRIPT_FILENAME'])) in the
callback function.
Output buffers are stackable, that is, you may call
ob_start while another
ob_start is active. Just make
sure that you call ob_end_flush
the appropriate number of times. If multiple output callback
functions are active, output is being filtered sequentially
through each of them in nesting order.
&reftitle.parameters;
output_callback
An optional output_callback function may be
specified. This function takes a string as a parameter and should
return a string. The function will be called when
the output buffer is flushed (sent) or cleaned (with
ob_flush, ob_clean or similar
function) or when the output buffer
is flushed to the browser at the end of the request. When
output_callback is called, it will receive the
contents of the output buffer as its parameter and is expected to
return a new output buffer as a result, which will be sent to the
browser. If the output_callback is not a
callable function, this function will return &false;.
This is the callback signature:
stringhandlerstringbufferintphasebuffer
Contents of the output buffer.
phase
Bitmask of PHP_OUTPUT_HANDLER_* constants.
If output_callback returns &false; original
input is sent to the browser.
The output_callback parameter may be bypassed
by passing a &null; value.
ob_end_clean, ob_end_flush,
ob_clean, ob_flush and
ob_start may not be called from a callback
function. If you call them from callback function, the behavior is
undefined. If you would like to delete the contents of a buffer,
return "" (a null string) from callback function.
You can't even call functions using the output buffering functions like
print_r($expression, true) or
highlight_file($filename, true) from a callback
function.
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:
ConstantFunctionsPHP_OUTPUT_HANDLER_CLEANABLEob_clean,
ob_end_clean, and
ob_get_clean.
PHP_OUTPUT_HANDLER_FLUSHABLEob_end_flush,
ob_flush, and
ob_get_flush.
PHP_OUTPUT_HANDLER_REMOVABLEob_end_clean,
ob_end_flush, and
ob_get_flush.
&reftitle.returnvalues;
&return.success;
&reftitle.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 a
boolean parameter called erase
(which, if set to &false;, would prevent the output buffer from being
deleted until the script finished executing) to an
integer 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. See
the 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.
&reftitle.examples;
User defined callback function example