Question

我无法理解为什么连接到数据库的功能无法正常工作，如果变量中有任何错误，我会检查三次。

在第12行的class.php上使用mysql_error函数我收到以下错误：

No database selected

class.php

 <?php

class blog {
    private $host;
    private $username;
    private $password;
    private $db;
    private $link;

    public function __construct($host, $username, $password, $db){
    $this->link = mysql_connect($host, $username, $password, $db);
    mysql_select_db($this->db, $this->link) or die (mysql_error());

    }

    function get_content(){
    $sql = "SELECT * FROM content";
    $res = mysql_query($sql);
    while($row = mysql_fetch_assoc($res)){
        echo '<h1>'.$row['title'].'</h1>';
        echo '<p>'.$row['body'].'</p>';
        }
    }
}// End of Class
?>

的index.php

  <?php include 'includes/class.php' ?>
<?php


//Setup Connection
$obj = new blog('localhost', 'root', '', 'blog');

//Connect to DB

?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<link rel="stylesheet" type="text/css" href="css/style.css" mce_href="styles1.css">
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>Mi Blog</title>
</head>

<body>

<div id="page-wrap">
    <?php $obj->get_content() ?>
</div>


</body>
</html>

Answer 1

您正在使用$this->db但从未设置它。试试这个：

public function __construct($host, $username, $password, $db){
    $this->db = $db;
    $this->link = mysql_connect($host, $username, $password, $db);
    mysql_select_db($this->db, $this->link) or die (mysql_error());
}

Answer 2

您未能设置$this->db。

Answer 3

首先

mysql_select_db($this->db, $this->link) or die (mysql_error());

应该是：

mysql_select_db($db, $this->link) or die (mysql_error());

和

$res = mysql_query($sql);

应该是

$res = mysql_query($sql, $this->link);

PHP：未选择数据库

3 个答案: