PHP5 Mysqli class is not outputting data - php

Question

So i am trying to make a backup class and this is what I have so far. Issue is the $tbl_data is empty. What am I doing wrong.
The connection to the database is successful.
Without the 'echo $tbl_data', the '$current_table - current table' output is correct but if 'echo $tbl_data' is used, only the first table is shown ( trying to backup two tables to begin with ).
class mBackup{
private $_connection = ""; //db connection var
private $output = ""; //sql output
private $tbl_data = "";
private $tbl_row = "";
private $nfields = "";
private $create_table_query = "";
private $create_table_output = "";
public function __construct($dbhost,$dbname,$dbuser,$dbpassword){
$this->_connection = new mysqli($dbhost,$dbuser,$dbpassword,$dbname);
//possible connection error
if($this->_connection->connect_errno){
echo "Failed to connect to the DB";
}
else{
echo "Connected<br />";
}
}
public function backup_db(){
//get the table names from the DB and store in an array
$result = $this->_connection->query("SHOW TABLES");
//get the TABLE names
while($row = $result->fetch_row())
{
$table_names[] = $row[0];
}
//For each table
foreach($table_names as $current_table)
{
echo $current_table." - current table<br />"; //debug
$tbl_data = "";
$tbl_row = "";
$nfields = "";
$create_table_query = "";
$create_table_output = "";
//SELECT Everything from the table in use
$query = $this->_connection->prepare("SELECT * FROM ?");
$query->bind_param('s', $current_table);
$query->execute();
$query->bind_result($tbl_data);
$query->fetch();
echo $tbl_data."<br/>";
}
}

Answer 1

Try something like:
while ($query->fetch()) {
echo $tbl_data;
}
and see if that gets you anything. From the little that I know, bind_result binds columns in the result set to variables. If your table has 5 columns, you should have bind_result($var1, $var2, $var3, $var4, $var5) but since your number of columns are going to change depending on the table, I don't know if bind_result will give you what you need.
Try closing the prepared statement after every loop
$query->close();
or resetting.
$query->reset()

Answer 2

You can't use ? for the table name. See the second note in http://www.php.net/manual/en/mysqli.prepare.php for the allowed places for markers. So you'll have to construct the query by normal variable interpolateion:
$select = sprintf("SELECT * FROM `%s`", $current_table);
$result = $this->_connection->query($select);