CodeIgniter makes working with files uploaded through a form much simpler and more secure than using PHP’s $_FILES array directly. This extends the File class and thus gains all of the features of that class. It provides a raw interface to the uploaded files with a few small features.

Uploading a file involves the following general process:

• An upload form is displayed, allowing a user to select a file and upload it.
• When the form is submitted, the file is uploaded to the destination you specify.
• Along the way, the file is validated to make sure it is allowed to be uploaded based on the preferences you set.
• Once uploaded, the user will be shown a success message.

1. Copy and Paste the following lines in app/Config/Routes.php

$routes->add('document/', 'Document::upload_form');
$routes->post('document/upload', 'Document::upload');

2. Create an upload_file.php file in the app/Views/ directory

<?php 
$attr = 'class="form-horizontal" id="add_client_form" autocomplete="off"';
echo form_open_multipart("document/upload", $attr);
?>

<div class="form-group">
    <label class="col-sm-2 control-label">File</label>
    <div class="col-md-4">
        <input type="file" id="file" name="file">
        <p class="help-block">Allowed types (.jpg, .png, .gif, .pdf)</p>
    </div>
    <div class="col-md-6"></div>
</div>

3. Create a controller file Document.php in the app/Controllers/ directory.

<?php 
namespace App\Controllers;

use App\Controllers\BaseController;

class Document extends BaseController {

    public function __construct() {
    
        helper(['url', 'form', 'array']);
    
    }
    
    public function upload_form() {
        echo view("upload_file");
    }
    
    public function upload() {
        $path               = 'uploads/';
        $file               = $this->request->getFile('file');
        $upload_file        = $this->uploadFile($path, $file);
        
        if($upload_file)
            echo "File uploaded successfully @ ".$upload_file;
    }
    
    public function uploadFile($path, $image) {
        if ($image->isValid() && ! $image->hasMoved()) {
            $newName = $image->getRandomName();
            $image->move('./'.$path, $newName);
            return $path.$image->getName();
        }
        return "";
    }
}