stream_filter_prepend()

(PHP 4 >= 4.3.0, PHP 5, PHP 7)

Attach a filter to a stream

说明

stream_filter_prepend(resource $stream,string $filtername[,int $read_write[,mixed $params]]): resource

Adds$filternameto the list of filters attached to$stream.

参数

$stream

The target stream.

$filtername

The filter name.

$read_write

By default,stream_filter_prepend()will attach the filter to theread filter chainif the file was opened for reading (i.e. File Mode:r, and/or+). The filter will also be attached to thewrite filter chainif 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 the$read_writeparameter to override this behavior.Seestream_filter_append()for an example of using this parameter.

$params

This filter will be added with the specified$paramsto thebeginningof the list and will therefore be called first during stream operations. To add a filter to the end of the list,usestream_filter_append().

返回值

Returns a resource on success orFALSEon failure. The resource can be used to refer to this filter instance during a call tostream_filter_remove().

FALSEis returned if$streamis not a resource or if$filternamecannot be located.

更新日志

注释

Note:When using custom (user) filters
stream_filter_register()must be called first in order to register the desired user filter to$filtername.

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 prepended to a stream, data in the internal buffers, which has already been processed through other filters willnotbe reprocessed through the new filter at that time. This differs from the behavior ofstream_filter_append().

Note:When a filter is added for read and write, two instances of the filter are created.stream_filter_prepend()must be called twice withSTREAM_FILTER_READandSTREAM_FILTER_WRITEto get both filter resources.

参见

• stream_filter_register()Register a user defined stream filter
• stream_filter_append()Attach a filter to a stream