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PHP ob_start
PHP original manual for ob_start
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ob_start
(PHP 4, PHP 5, PHP 7) ob_start — Turn on output buffering
Description
bool ob_start
([ callable $output_callback = NULL
[, int $chunk_size = 0
[, int $flags = PHP_OUTPUT_HANDLER_STDFLAGS
]]] )
The contents of this internal buffer may be copied into a string variable
using ob_get_contents(). To output what is stored in
the internal buffer, use ob_end_flush(). Alternatively,
ob_end_clean() will silently discard the buffer
contents.
Warning
Some web servers (e.g. Apache) change the working directory of a script
when calling the callback function. You can change it back by e.g.
chdir(dirname($_SERVER['SCRIPT_FILENAME'])) in the
callback function.
Output buffers are stackable, that is, you may 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.
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:
string handler
( string $buffer
[, int $phase
] )
-
buffer
-
Contents of the output buffer.
-
phase
-
Bitmask of
PHP_OUTPUT_HANDLER_* constants.
If output_callback returns FALSE original
input is sent to the browser.
The output_callback parameter may be bypassed
by passing a NULL value.
ob_end_clean(), ob_end_flush(),
ob_clean(), ob_flush() and
ob_start() may not be called from a callback
function. If you call them from callback function, the behavior is
undefined. If you would like to delete the contents of a buffer,
return "" (a null string) from callback function.
You can't even call functions using the output buffering functions like
print_r($expression, true) or
highlight_file($filename, true) from a callback
function.
Note:
ob_gzhandler() function exists to
facilitate sending gz-encoded data to web browsers that support
compressed web pages. ob_gzhandler() determines
what type of content encoding the browser will accept and will return
its output accordingly.
-
chunk_size
-
If the optional parameter chunk_size is passed, the
buffer will be flushed after any output call which causes the buffer's
length to equal or exceed chunk_size. The default
value 0 means that the output function will only be
called when the output buffer is closed.
Prior to PHP 5.4.0, the value 1 was a special case
value that set the chunk size to 4096 bytes.
-
flags
-
The flags parameter is a bitmask that controls
the operations that can be performed on the output buffer. The default
is to allow output buffers to be cleaned, flushed and removed, which
can be set explicitly via
PHP_OUTPUT_HANDLER_CLEANABLE |
PHP_OUTPUT_HANDLER_FLUSHABLE |
PHP_OUTPUT_HANDLER_REMOVABLE, or
PHP_OUTPUT_HANDLER_STDFLAGS as shorthand.
Each flag controls access to a set of functions, as described below:
Return Values
Returns TRUE on success or FALSE on failure.
Examples
Example #1 User defined callback function example
<?php
function callback($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 uneraseable output buffer in a way compatible with both PHP 5.3 and 5.4
<?php
if (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);
}
?>
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