问题，您分别尝试了realpath和APPPATH？
在Codeigniter中APPPATH指向应用程序文件夹。

示例：（将您的文件夹放置在应用程序文件夹之外，只是说如果您没有这样做）让我们假设要放置名为images的文件的文件夹。

因此，您需要将realpath(）和APPPATH组合起来

$image_path = realpath(APPPATH . '../images');

并将其传递给配置

$config['upload_path'] = $image_path;

创建您的文件上传目录，例如在应用程序目录之外或在CI的根目录中上传，并按如下所示设置上传路径：-

$config['upload_path'] = realpath(FCPATH.'uploads');

FCPATH：index.php所在的前端控制器的路径（CI的根目录）
上面的代码在服务器和本地都运行。

这是在CI中完成文件上载的方式

$cat_image_name = $_FILES["cat_image"]["name"] ; 

//file uploading params
$config['upload_path'] = './uploaded_files/categories';
$config['allowed_types'] = 'gif|jpg|png';
$config['file_name'] = $image_id."_ipad";
$config['remove_spaces'] = TRUE;

//Loading Library - File Uploading
$this->load->library('upload', $config);

//Upload the image(Ipad)
if (!empty($cat_image_name)) 
{
  $this->upload->do_upload('cat_image');
  $data = array('upload_data' => $this->upload->data());
  $category_image_ipad = $data['upload_data']['file_name'];
  $img_extension = $data['upload_data']['file_ext'];
}

试试这个

$config['upload_path'] = '../uploads/;

对我来说效果很好

使用它：

$config['upload_path'] = $_SERVER['DOCUMENT_ROOT']."/uploads/";
//$this->config->item('upload_path');

文件上载需要多部分表单。为此，您必须包含表单帮助器。
后藤config文件夹，单击autoload并找到$autoload['helper'] = array();，然后输入“form”：

$autoload['helper'] = array('form');

对于控制器：
$config =数组（

'upload_path' => "./assets/",
    'allowed_types' => "gif|jpg|png|jpeg",
    'overwrite' => TRUE,
    'max_size' => "2048000",
    'max_height' => "768",
    'max_width' => "1024"
    );

    $this->load->library('upload', $config);

    if(!$this->upload->do_upload()){
        $errors = array('error' => $this->upload->display_errors());
        $post_image = 'noimage.jpg';
    } else {
        $data = array('upload_data' => $this->upload->data());
        $post_image = $_FILES['userfile']['name'];
    }

    $this->user_model->create_photo($post_image);
    redirect('');
}

对于型号：

public function create_photo($post_image){

    $data = array(
        'pri' => $this->input->post('price'),
        'descrip' => $this->input->post('title'),
        'post_image' => $post_image
    );

    return $this->db->insert('table_name', $data);
}

在Windows和Linux上测试：

$path = realpath(".");
$path .= "/uploads/profile_images";

这里uploads是根目录下的uploads目录。

FCPATH：index.php所在的前端控制器路径或根文件夹
APPPATH：****应用程序文件夹

在root文件夹下创建uploads文件夹：

$config['upload_path'] = realpath(FCPATH.'uploads');

在application文件夹下创建uploads文件夹：

$config['upload_path'] = realpath(APPPATH.'uploads');

如果：如果您在root文件夹之外创建了uploads文件夹：

$config['upload_path'] = realpath($_SERVER['DOCUMENT_ROOT'].'/uploads');

事情很简单：
只需将所有的$config文件复制到一个名为upload.php的新php文件中，然后将其放在cofig文件夹中。
你的路径会正常工作。
下面是upload.php文件的内容：

<?php

    $config['upload_path'] = site_url().'uploads';
    $config['allowed_types'] = 'gif|jpg|png|jpeg|html|pdf';
    $config['max_size'] = 0;
    $config['max_width']  = 0;
    $config['max_height']  = 0;
    $config['file_ext_tolower']  = TRUE;
    $config['overwrite']  = FALSE;
    $config['max_filename']  = 0;
    $config['encrypt_name']  = TRUE;
    $config['remove_spaces']  = TRUE;
    $config['detect_mime']  = TRUE;
    $config['mod_mime_fix']  = TRUE;
?>

但请同时在upload_file控制器中保留$config数据。例如：

public function do_upload(){

    $config['upload_path'] = 'uploads';
    $config['allowed_types'] = 'gif|jpg|png|jpeg|html|pdf';
    $config['max_size'] = 0;
    $config['max_width']  = 0;
    $config['max_height']  = 0;
    $config['file_ext_tolower']  = TRUE;
    $config['overwrite']  = FALSE;
    $config['max_filename']  = 0;
    $config['encrypt_name']  = TRUE;
    $config['remove_spaces']  = TRUE;
    $config['detect_mime']  = TRUE;
    $config['mod_mime_fix']  = TRUE;

//Alternately you can set preferences by calling the initialize function. Useful if you auto-load the class:

   $this->upload->initialize($config);

            if (!$this->upload->do_upload('userfile'))
    {
        $error = array('error' => $this->upload->display_errors());

        $this->load->view('upload_form', $error);
    }
    else
    {
        $data = array('upload_data' => $this->upload->data());

        $this->load->view('upload_success', $data);
    }
    }

很简单...