未定義變量：con在C：\ wamp \ www \ android_connect \ db_connect.php在線

Question

在我的Android應用程序中。我試圖驗證用戶，因爲我寫了一個PHP腳本來建立連接到數據庫，但不幸的是我得到以下錯誤 -

「Undefined variable：con in C：\ wamp \ WWW \ android_connect \ db_connect.php上線「

爲了解決這個錯誤我已經宣佈」$ CON「爲全局變量，但仍然得到同樣的錯誤 -

我db_connect.php代碼---

<?php 

/** 
* A class file to connect to database 
*/ 
class DB_CONNECT 
{ 

    private $con;  

    // constructor 
    function __construct() 
    { 
     // connecting to database 
     $this->connect(); 
    } 

    // destructor 
    function __destruct() 
    { 
     // closing db connection 
     $this->close(); 
    } 

    /** 
    * Function to connect with database 
    */ 
    function connect() 
    { 
     // import database connection variables 
     require_once __DIR__ . '/db_config.php'; 

     // Connecting to mysql database    
    $con = mysqli_connect(DB_SERVER, DB_USER, DB_PASSWORD, DB_DATABASE); 

     // Selecing database 
     $db = mysqli_select_db($con, DB_DATABASE); 
     // returing connection cursor 
     return $con; 
    } 

    /*  
    * Function to close db connection 
    */ 
    function close() 
    { 
    // closing db connection 
     mysqli_close($con); 

    } 
} 

?> 

請幫助。謝謝..！

Answer 1

<?php 

/** 
* A class file to connect to database 
*/ 
class DB_CONNECT 
{ 

    private $con;  

    // constructor 
    function __construct() 
    { 
     // connecting to database 
     $this->connect(); 
    } 

    // destructor 
    function __destruct() 
    { 
     // closing db connection 
     $this->close(); 
    } 

    /** 
    * Function to connect with database 
    */ 
    function connect() 
    { 
     // import database connection variables 
     require_once __DIR__ . '/db_config.php'; 

     // Connecting to mysql database    
     $this->con = mysqli_connect(DB_SERVER, DB_USER, DB_PASSWORD, DB_DATABASE); 

     // Selecing database 
     $db = mysqli_select_db($this->con, DB_DATABASE); 

     // returing connection cursor 
     return $this->con; 
    } 

    /*  
    * Function to close db connection 
    */ 
    function close() 
    { 
     // closing db connection 
     mysqli_close($this->con); 
    } 
} 

?> 

使用$this->con，而不是$con，作爲$con是一個類變量，並且使用的是作爲一個局部變量。

Answer 2

問題 - 在功能connect()$con變量未分配的$con價值，你給公共變量，同樣，在close()功能它沒有引用到公共變量。

更改功能連接爲 -

function connect() 
    { 
     // import database connection variables 
     require_once __DIR__ . '/db_config.php'; 

     // Connecting to mysql database    
    $this->con = mysqli_connect(DB_SERVER, DB_USER, DB_PASSWORD, DB_DATABASE); 

     // Selecing database 
     $db = mysqli_select_db($con, DB_DATABASE); 
     // returing connection cursor 
     return $con; 
    } 

和功能接近（）作爲 -

function close() 
    { 
    // closing db connection 
     mysqli_close($this->con); 

    } 

終極密碼 -

<?php 

/** 
* A class file to connect to database 
*/ 
class DB_CONNECT 
{ 

    private $con;  

    // constructor 
    function __construct() 
    { 
     // connecting to database 
     $this->connect(); 
    } 

    // destructor 
    function __destruct() 
    { 
     // closing db connection 
     $this->close(); 
    } 

    /** 
    * Function to connect with database 
    */ 
    function connect() 
    { 
     // import database connection variables 
     require_once __DIR__ . '/db_config.php'; 

     // Connecting to mysql database    
    $this->con = mysqli_connect(DB_SERVER, DB_USER, DB_PASSWORD, DB_DATABASE); 

     // Selecing database 
     $db = mysqli_select_db($con, DB_DATABASE); 
     // returing connection cursor 
     return $con; 
    } 

    /*  
    * Function to close db connection 
    */ 
    function close() 
    { 
    // closing db connection 
     mysqli_close($this->con); 

    } 
} 

?>