ob_start
(PHP 4, PHP 5)
ob_start — Turn on output buffering
说明
bool ob_start
([ callback $output_callback
[, int $chunk_size
[, bool $erase
]]] )
This function will turn output buffering on. While output buffering is
active no output is sent from the script (other than headers), instead the
output is stored in an internal buffer.
The contents of this internal buffer may be copied into a string variable
using ob_get_contents(). To output what is stored in
the internal buffer, use ob_end_flush(). Alternatively,
ob_end_clean() will silently discard the buffer
contents.
Warning
Some web servers (e.g. Apache) change the working directory of a script
when calling the callback function. You can change it back by e.g.
chdir(dirname($_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.
参数
-
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
ob_end_flush() is called, 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.
If the callback function has two parameters, the second parameter is
filled with a bit-field consisting of
PHP_OUTPUT_HANDLER_START,
PHP_OUTPUT_HANDLER_CONT and
PHP_OUTPUT_HANDLER_END.
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:
In PHP 4.0.4, ob_gzhandler() was introduced 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
.
Default value 0 means that the function is called only in the end,
other special value 1 sets chunk_size
to 4096.
-
erase
-
If the optional parameter erase
is set to FALSE,
the buffer will not be deleted until the script finishes (as of PHP 4.3.0).
返回值
如果成功则返回 TRUE，失败则返回 FALSE。
范例
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();
?>
<html>
<body>
<p>It's like comparing oranges to oranges.</p>
</body>
</html>