php - MySQL错误参数

Question

我有两个参数错误：
mysqli_select_db（）期望参数1为mysqli，给定空值
mysqli_error（）需要1个参数，给定0

class MyMySQLi
    {
private $connected = false;
private $hostname = "localhost";
private $username = "root";
private $password = "****";
private $database = "****";
private $link;

    public function Connect()
{
     mysqli_select_db($this->link,$this->database) or $this->error(mysqli_error());

    $this->connected = true;
    $this->link = mysqli_connect($this->hostname, $this->username, $this->password) or $this->error(mysqli_error());

}
public function MySQLi($host, $user, $pass, $db)
{
    $this->connected = false;   
    $this->hostname = $host;
    $this->username = $user;
    $this->password = $pass;
    $this->database = $db;
}

public function IsConnected()
{
    if ($this->connected)
    {
        return true;
    }

    return false;
}

谢谢你！我还有一个错误：
mysqli_error（）需要1个参数，给定0

            $this->connected = true;
            $this->link = mysqli_connect($this->hostname, $this->username, 
            $this->password) or $this->error(mysqli_error());
            mysqli_select_db($this->link,$this->database) or $this->error(mysqli_error()); 

Answer 1

在设置mysqli_set_db之前，您正在调用$this->link。还需要传递给它的数据库对象：
mysqli_error