php - PHP类函数中的 fatal error "Cannot access empty property"在哪里？

Question

这段代码有什么问题？

<?php

class users {

  var $user_id,
      $f_name,
      $l_name,
      $db_host,
      $db_user,
      $db_name,
      $db_table;

  function users() {
      $this->$db_host = 'localhost';
      $this->$db_user = 'root';
      $this->$db_name = 'input_oop';
      $this->$db_table = 'users';
  }

  function userInput($f_name, $l_name) {
      $dbc = mysql_connect($this->db_host , $this->db_user, "") or die ("Cannot connect to database : " .mysql_error());
      mysql_select_db($this->db_name) or die (mysql_error());
      $query = "insert into $this->db_table values (NULL, \"$f_name\", \"$l_name\")";
      $result = mysql_query($query);
      if(!$result) die (mysql_error());

      $this->userID = mysql_insert_id();

      mysql_close($dbc);

      $this->first_name = $f_name;
      $this->last_name = $l_name;
  }

  function userUpdate($new_f_name, $new_l_name) {
      $dbc = mysql_connect($this->db_host, $this->db_user, "") or die (mysql_error());
      mysql_select_db($this->db_name) or die (mysql_error());

      $query = "UPDATE $this->db_table set  = \"$new_f_name\" , \"$new_l_name\" WHERE user_id = \"$this->user_id\"";
      $result = mysql_query($query);

      $this->f_name = $new_f_name;
      $this->l_name = $new_l_name;
      $this->user_id = $user_id;

      mysql_close($dbc);
  }

  function userDelete() {
      $dbc = mysql_connect($this->db_host, $this->db_user, "") or die (mysql_error());
      mysql_select_db($this->db_name) or die (mysql_error());

      $query = "DELETE FROM $this->db_table WHERE $user_id = \"$this->user_id\"";

      mysql_close($dbc);
  } 
}
?>

错误是:

Fatal error: Cannot access empty property in C:\xampp\htdocs\jordan_pagaduan\class.php on line 15.

Answer 1

访问 class-property从类的方法内部，您必须使用 $this->propertyName，而不是 $this->$propertyName。

这意味着您的user_input() 方法应该这样写:

function user_input() {
    $this->db_host = 'localhost';
    $this->db_user = 'root';
    $this->db_name = 'input_oop';
    $this->db_table = 'users';
}

(其他地方可能需要做同样的修改)

使用您编写的内容，永远不会设置 $this->db_user ；并且，稍后，当使用这个时:

$dbc = mysql_connect($this->db_host , $this->db_user, "")

$this->db_user 为空；这意味着 mysql_connect将使用 default value -- 从错误消息来看，在您的情况下，它似乎是 ODBC。

(与其他属性相同 - 但我以这个为例，因为 ODBC 默认值出现在您发布的错误消息中:它是最显而易见的选择。)