Php 严格标准：只能通过引用传递变量”；创建thumnail时出错

我在请求时使用php制作缩略图。但是我的错误日志很快就被填满了，因为我在第13行遇到了一个错误 PHP严格标准：第13行的/public_html/xxxxxx/thumbnail.PHP中只能通过引用传递变量

   $sExtension = strtolower(end(explode('.', $sImagePath)));

我的完整代码在这里

     <?php
   $sImagePath = $_GET["file"];

     $iThumbnailWidth = (int)$_GET['width'];
   $iThumbnailHeight = (int)$_GET['height'];
  $iMaxWidth = (int)$_GET["maxw"];
    $iMaxHeight = (int)$_GET["maxh"];

 if ($iMaxWidth && $iMaxHeight) $sType = 'scale';
    else if ($iThumbnailWidth && $iThumbnailHeight) $sType = 'exact';

 $img = NULL;
 $sExtension = strtolower(end(explode('.', $sImagePath)));
 if ($sExtension == 'jpg' || $sExtension == 'jpeg') {

    $img = @imagecreatefromjpeg($sImagePath)
    or die("Cannot create new JPEG image");

  } else if ($sExtension == 'png') {

  $img = @imagecreatefrompng($sImagePath)
    or die("Cannot create new PNG image");

   } else if ($sExtension == 'gif') {

   $img = @imagecreatefromgif($sImagePath)
     or die("Cannot create new GIF image");

}

  if ($img) {

 $iOrigWidth = imagesx($img);
 $iOrigHeight = imagesy($img);

 if ($sType == 'scale') {


    $fScale = min($iMaxWidth/$iOrigWidth,
          $iMaxHeight/$iOrigHeight);

    if ($fScale < 1) {

        $iNewWidth = floor($fScale*$iOrigWidth);
        $iNewHeight = floor($fScale*$iOrigHeight);

        $tmpimg = imagecreatetruecolor($iNewWidth,
                           $iNewHeight);

        imagecopyresampled($tmpimg, $img, 0, 0, 0, 0,
        $iNewWidth, $iNewHeight, $iOrigWidth, $iOrigHeight);


        imagedestroy($img);
        $img = $tmpimg;
     }     

   } else if ($sType == "exact") {


     $fScale = max($iThumbnailWidth/$iOrigWidth,
          $iThumbnailHeight/$iOrigHeight);

       if ($fScale < 1) {

        $iNewWidth = floor($fScale*$iOrigWidth);
        $iNewHeight = floor($fScale*$iOrigHeight);

        $tmpimg = imagecreatetruecolor($iNewWidth,
                        $iNewHeight);
        $tmp2img = imagecreatetruecolor($iThumbnailWidth,
                        $iThumbnailHeight);


        imagecopyresampled($tmpimg, $img, 0, 0, 0, 0,
        $iNewWidth, $iNewHeight, $iOrigWidth, $iOrigHeight);


        if ($iNewWidth == $iThumbnailWidth) {

            $yAxis = ($iNewHeight/2)-
                ($iThumbnailHeight/2);
            $xAxis = 0;

        } else if ($iNewHeight == $iThumbnailHeight)  {

            $yAxis = 0;
            $xAxis = ($iNewWidth/2)-
                ($iThumbnailWidth/2);

        } 

        imagecopyresampled($tmp2img, $tmpimg, 0, 0,
                   $xAxis, $yAxis,
                   $iThumbnailWidth,
                   $iThumbnailHeight,
                   $iThumbnailWidth,
                   $iThumbnailHeight);

        imagedestroy($img);
        imagedestroy($tmpimg);
        $img = $tmp2img;
      }    

     }


    header("Content-type: image/jpeg");
    imagejpeg($img);

  }

 ?>

如果您有任何帮助，我们将不胜感激

尝试这样做：

 $sExtension = explode('.', $sImagePath);

$file_extension = strtolower(end($sExtension));

end

需要引用，因为它修改数组的内部表示形式