php 错误处理(文件上传）中的错误

我想在上传的图像大小超过 3MB 时发出错误消息。这是我当前的代码。当图像超过 3MB 时，它应该发出错误消息，但它什么也不做。我的代码有什么问题？

if ( $_FILES['file']['size'] != 0 ) 
{
 //image check start
 if ((($_FILES["file"]["type"] == "image/gif")
 || ($_FILES["file"]["type"] == "image/jpeg")
 || ($_FILES["file"]["type"] == "image/png")
 || ($_FILES["file"]["type"] == "image/pjpeg"))
 && ($_FILES["file"]["size"] < 3072000))
 //image check end
 {
      if (file_exists($upload_path."/".$_FILES["file"]["name"])) 
      {
           $file_tmp = $_FILES["file"]["name"];
      } //Link if there is already a file with identical file name
      else
      {
           $photoid = $upfile_idx.".".substr($_FILES['file']['name'],-3);
           move_uploaded_file($_FILES["file"]["tmp_name"], $upload_path."/".$photoid);
           $file_tmp = $photoid ;
      } //Upload the image file into upload folder and generate an id for the image
  }
  else
  {
      error("Maximum image size exceeded or invalid file format.");
  }
}
//insert $file_tmp into database here
----------
Error code (added later)
function error($msg)
{
  echo "<script>alert('"$msg'");history.go(-1);</script>";
  exit;
}

我发现了问题所在。在我的php.ini文件中，有"upload_max_filesize = 3M"，显然这就是导致所有问题的原因。当我将其更改为"upload_max_filesize = 4M"时，一切正常。谢谢大家的帮助。