php中stream_wrapper_register的实际用途是什么？

Question

I am new learner in php. and i found 'stream_wrapper_register' function in php documentation. Here is link http://php.net/manual/en/function.stream-wrapper-register.php .

Can anyone please help me to understand exact use of this function in projects. I didn't found any realtime examples for this.

Answer 1

Here is an example, how to use data from variable with function that only reads from files (method Image of FPDF class is 'replaced' by method MemImage ).

http://www.fpdf.org/en/script/script45.php

require('fpdf.php');

//Stream handler to read from global variables
class VariableStream
{
    var $varname;
    var $position;

    function stream_open($path, $mode, $options, &$opened_path)
    {
        $url = parse_url($path);
        $this->varname = $url['host'];
        if(!isset($GLOBALS[$this->varname]))
        {
            trigger_error('Global variable '.$this->varname.' does not exist', E_USER_WARNING);
            return false;
        }
        $this->position = 0;
        return true;
    }

    function stream_read($count)
    {
        $ret = substr($GLOBALS[$this->varname], $this->position, $count);
        $this->position += strlen($ret);
        return $ret;
    }

    function stream_eof()
    {
        return $this->position >= strlen($GLOBALS[$this->varname]);
    }

    function stream_tell()
    {
        return $this->position;
    }

    function stream_seek($offset, $whence)
    {
        if($whence==SEEK_SET)
        {
            $this->position = $offset;
            return true;
        }
        return false;
    }

    function stream_stat()
    {
        return array();
    }
}

class PDF_MemImage extends FPDF
{
    function PDF_MemImage($orientation='P', $unit='mm', $format='A4')
    {
        $this->FPDF($orientation, $unit, $format);
        //Register var stream protocol
        stream_wrapper_register('var', 'VariableStream');
    }

    function MemImage($data, $x=null, $y=null, $w=0, $h=0, $link='')
    {
        //Display the image contained in $data
        $v = 'img'.md5($data);
        $GLOBALS[$v] = $data;
        $a = getimagesize('var://'.$v);
        if(!$a)
            $this->Error('Invalid image data');
        $type = substr(strstr($a['mime'],'/'),1);
        $this->Image('var://'.$v, $x, $y, $w, $h, $type, $link);
        unset($GLOBALS[$v]);
    }

    function GDImage($im, $x=null, $y=null, $w=0, $h=0, $link='')
    {
        //Display the GD image associated to $im
        ob_start();
        imagepng($im);
        $data = ob_get_clean();
        $this->MemImage($data, $x, $y, $w, $h, $link);
    }
}