php mysqli数据库连接失败？

Question

Goodday,

I get an strange error.

this is my code:

<?php
$con=mysqli_connect("localhost","root","","testdatabase");

class database{
    public function select($tableName){
        $result = mysqli_query($con,"SELECT * FROM ".$tableName);       
    }       
}

$database = new database();
?>

The error message is that $con is an undefined variable. But i define $con on line number 2?

when i var_dump con it also says NULL.

What am i doing wrong?

Answer 1

If you want to access to your $con var in a method or function, you have to globalize it inside your code :

public function select($tableName){
    global $con;
    $result = mysqli_query($con,"SELECT * FROM ".$tableName);       
}

But you shouldn't do that, globals are evil !

This is how your code should be :

<?php
class database{
    protected $con;

    public function __construct($host, $user, $password, $dbname){
        $this->con = mysqli_connect($host, $user, $password, $dbname);
    }

    public function select($tableName){
        $result = mysqli_query($this->con,"SELECT * FROM ".$tableName);       
    }       
}

$database = new database("localhost", "root", "", "testdatabase");
?>