stream_filter_append
(PHP 4 >= 4.3.0, PHP 5)
stream_filter_append — Attach a filter to a stream
说明
$stream
, string $filtername
[, int $read_write
[, mixed $params
]] )
Adds filtername to the list of filters
attached to stream.
参数
-
stream -
The target stream.
-
filtername -
The filter name.
-
read_write -
By default, stream_filter_append() will attach the filter to the read filter chain if the file was opened for reading (i.e. File Mode: r, and/or +). The filter will also be attached to the write filter chain if the file was opened for writing (i.e. File Mode: w, a, and/or +).
STREAM_FILTER_READ,STREAM_FILTER_WRITE, and/orSTREAM_FILTER_ALLcan also be passed to theread_writeparameter to override this behavior. -
params -
This filter will be added with the specified
paramsto the end of the list and will therefore be called last during stream operations. To add a filter to the beginning of the list, use stream_filter_prepend() .
返回值
Returns a resource which can be used to refer to this filter instance during a call to stream_filter_remove() .
更新日志
| 版本 | 说明 |
|---|---|
| 5.1.0 |
Prior to PHP 5.1.0, this function returns TRUE on success
或者在失败时返回 FALSE .
|
范例
Example #1 Controlling where filters are applied
<?php
$fp = fopen ( 'test.txt' , 'w+' );
stream_filter_append ( $fp , "string.rot13" , STREAM_FILTER_WRITE );
fwrite ( $fp , "This is a test\n" );
rewind ( $fp );
fpassthru ( $fp );
fclose ( $fp );
?> 注释
Note: When using custom (user) filters
stream_filter_register() must be called first in order to register the desired user filter tofiltername.
Note: Stream data is read from resources (both local and remote) in chunks, with any unconsumed data kept in internal buffers. When a new filter is appended to a stream, data in the internal buffers is processed through the new filter at that time. This differs from the behavior of stream_filter_prepend() .
Note: When a filter is added for read and write, two instances of the filter are created. stream_filter_append() must be called twice with
STREAM_FILTER_READandSTREAM_FILTER_WRITEto get both filter resources.
参见
- stream_filter_register() - Register a user defined stream filter
- stream_filter_prepend() - Attach a filter to a stream
- stream_get_filters() - 获取已注册的数据流过滤器列表
用户评论:
[#1] dlvoy [2008-07-23 00:20:38]
While using compression filters on a large set of files during one script invocation i've got
Fatal error: Allowed memory size of xxx bytes exhausted
even when my max memory limit settings was insane high (128MB)
Workaround is to remember to remove filter after work done with stream_filter_remove:
<?php
foreach($lot_of_files as $filename)
{
$fp = fopen($filename, 'rb');
$filter_params = array('level' => 2, 'window' => 15, $memory => 6);
$s_filter = stream_filter_append($fp, 'zlib.deflate', STREAM_FILTER_READ, $filter_params);
// here stream-operating code
stream_filter_remove($s_filter);
fclose($fp);
}
?>
[#2] net_navard at yahoo dot com [2005-12-12 22:47:00]
Hello firends
The difference betweem adding a stream filter first or last in the filte list in only the order they will be applied to streams.
For example, if you're reading data from a file, and a given filter is placed in first place with stream_filter_prepend()the data will be processed by that filter first.
This example reads out file data and the filter is applied at the beginning of the reading operation:
<?php
$fp = fopen("test.txt", "r");
stream_filter_prepend($fp, "string.rot13",
STREAM_FILTER_READ);
// read file data
$contents=fread($fp,1024);
// file data is first filtered and stored in $contents
echo $contents;
fclose($fp);
?>
On the other hand, if stream_filter_append() is used, then the filter will be applied at the end of the data operation. The thing about this is only the order filters are applied to streams. Back to the example, it's not the same thing removing new lines from file data and then counting the number of characters, than performing the inverse process. In this case, the order that filters are applied to stream is important.
This example writes a test string to a file. The filter is applied at the end of the writing operation:
<?php
$fp = fopen("test.txt", "w+");
stream_filter_append($fp, "string.rot13",
STREAM_FILTER_WRITE);
fwrite($fp, "This is a test\n"); // string data is
first written, then ROT13 tranformed and lastly
written to file
rewind($fp);
$contents=fread($fp,512);
fclose($fp);
echo $contents;
?>
In the first case, data is transformed at the end of the writing operation, while in the second one, data is first filtered and then stored in $contents.
With Regards
Hossein