致命錯誤：未捕獲的錯誤：調用（）成員函數escape_string上的空

Question

我收到此錯誤

Fatal error: Uncaught Error: Call to a member function escape_string() on null in C:\xampp\htdocs\url\classes\shortener.php:19 Stack trace: #0 C:\xampp\htdocs\url\shorten.php(10): Shortener->makeCode('stackove...') #1 {main} thrown in C:\xampp\htdocs\url\classes\shortener.php on line 19

我設計我自己的網址縮短服務，但是當我測試它，它給了我這個錯誤。 我使用這個

此代碼是縮短文件，以獲得輸入網址 shorten.php

<?php 
session_start(); 
require_once 'classes/shortener.php'; 

$s = new Shortener; 

if(isset($_POST['url'])) { 
    $url = $_POST['url']; 

    if($code = $s->makeCode($url)) { 
     echo $code; 
    } else { 

    } 

} 

這是一個縮短的URL shortener.php文件

<?php 
class Shortener{ 
    protected $db; 

    public function _construct(){ 
     $this->db = new mysqli('localhost','root','','shortenedurl'); 
    } 

    protected function generateCode($num){ 
     return base_convert($num, 10, 36); 
    } 

    public function makeCode($url){ 
     $url = trim($url); 

     if(!filter_var($url, FILTER_VALIDATE_URL)) { 
      return ''; 
     } 
     $url = $this->db->escape_string($url); 

     $exists = $this->db->query("SELECT code FROM short_urls WHERE urlinput = '{$url}'"); 

     if($exists->num_rows) { 
      return $exists->fetch_object()->code; 
     } else { 
      $insert = $this->db->query("INSERT INTO short_urls(urlinput, created) VALUES ('{$url}', NOW())"); 

      $code = $this->generateCode($this->db->insert_id); 

      $this->db->query("UPDATE short_urls SET code ='{$code}' WHERE url ='{$url}'"); 

      return $code;  
     } 
    } 

    public function getUrl($code){ 
    } 

} 

Answer 1

構造需要以'_'中的兩個開頭，所以它必須是'__'。
所以你需要改變public function _construct(){這個public function __construct(){