希望这对您有所帮助：

• 您的do_upload方法应该如下所示：*

public function do_upload() 
{
    $config['upload_path'] = './upload/';
    $config['allowed_types']='gif|jpg|png';
    $this->load->library('upload', $config);
    if($this->upload->do_upload('image_file'))
    {
        $filename = $this->upload->data('file_name');
        echo  $filename;die;
    }
    else
    {
        print_r($this->upload->display_errors());
        die;
    }
}

更新：

set upload_max_filesize在您的php ini中大于2MB，
如果是wamp，则只需执行以下操作：
click on wamp => php => php settings => upload_max_filesize

我想你没听到这句台词。
上传文件的路径为：
$config [允许的类型]='gif| jpg格式|png“;

$this-〉上载-〉初始化（$config）;

$this-〉加载-〉库（'上载'，$config）;
如果（$this-〉上传-〉do_upload（'图像文件'））{

$filename = $this->upload->data('file_name');
    echo  $filename;die;
}
else
{
    print_r($this->upload->display_errors());
    die;
}