Wordpress theme functions not working when called - php

Question

I have a wordpress site and I want to save and do the database connection in my functions.php
So I can be calling it in my templates.
Here are the functions code in the in functions.php
<?php
function dbconnd() {
$server = "localhost";
$duser = "wpuser";
$dpass = "wppass";
$dbname = "wpdb";
$conn = new mysqli($server, $duser,$dpass, $dbname);
// Check connection
if ($conn->connect_error) {
die("Connection failed: " . $conn->connect_error);
}
}
?>
So in my main.php if I call dbconnd(); , it seems it's not working as it throws a fatal error as in the case below:
Fatal error: Call to a member function query() on a non-object in
/main.php on line 49
<?php
dbconnd();
$sql = "SELECT * FROM orderform WHERE status='last';";
$result = $conn->query($sql); //this is line 49
?>
But in case below when am not calling the function, it works perfectly
<?php
$server = "localhost";
$duser = "wpuser";
$dpass = "wppass";
$dbname = "wpdb";
$conn = new mysqli($server, $duser,$dpass, $dbname);
// Check connection
if ($conn->connect_error) {
die("Connection failed: " . $conn->connect_error);
}
$sql = "SELECT * FROM orderform WHERE status='last';";
$result = $conn->query($sql);
?>

Answer 1

The way you are doing right now, $conn is a local variable only inside the function. So you can't get the value outside the function that way.
The best solution would be this:
function dbconnd() {
$server = "localhost";
$duser = "wpuser";
$dpass = "wppass";
$dbname = "wpdb";
$conn = new mysqli($server, $duser,$dpass, $dbname);
// Check connection
if ($conn->connect_error) {
die("Connection failed: " . $conn->connect_error);
}
else
return $conn;
}
And then when you're going to call the function, run this:
$conn = dbconnd();
Also don't forget to include or require the functions.php file inside the php file calling it.