其中是致命错误“无法访问空属性”在PHP类中的函数？ [英] where is the fatal error "Cannot access empty property" in the PHP class function?

问题描述

此代码有什么问题？

<?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：

致命错误：无法在第15行访问C：\ xampp\htdocs\jordan_pagaduan\class.php中的空属性。

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

推荐答案

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

To access a class-property from inside a method of a class, you must use $this->propertyName, and not $this->$propertyName.

这意味着您的 user_input （）方法应该写成这样：

Which means your user_input() method should be written like this :

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

（您可能需要对其他地方进行相同的修改）

(you might have to do the same modification to other places)

根据您撰写的内容， $ this-> db_user 从不设置; ，以后使用时：

With what you have written, $this->db_user is never set ; and, later, when using this :

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

$ this-> db_user 为null;这意味着 mysql_connect 将使用默认值 - 在您的情况下，看起来是 ODBC ，从错误消息判断。

$this->db_user is null ; which means mysql_connect will use the default value -- which, in your case, appears to be ODBC, judging from the error message.

- 但我把这个例子，因为 ODBC 默认值存在于您发布的错误消息：它是最明显的选择。）

(same thing with the other properties -- but I took this one as an example, as the ODBC default-value was present in the error message you posted : it was the most obvious choice.)

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