global variable PHP not getting updated

In my code:

<?php

$var1 = 0; //I want `$var1` to retain its value in all functions `abc()` and `xyz()`

abc();

function abc()
{
    global $var1;
    $varDatabase = 10; //a value from database
    $var1 = &$varDatabase; //$var1 set as reference

    xyz(); //$var1 is changed in xyz() function

    echo $var1; //I expect value 110 here but it return last value 10
}

function xyz()
{
    global $var1;
    $var1 = $var1 + 100;
}

?>

My variable $var1 is set as a pointer/reference to another variable $varDatabase. $var1 is updated in a function xyz(), and I expect its new updated value in calling function after xyz() is executed. That is why I have set $var1 as global, but still it does not give me updated value after xyz() is executed.

All I want is$var1 to retain its value in all functions abc() and xyz()

Answer

Global variables are implemented by making the variable a reference to the corresponding $GLOBALS element, i.e.

global $var1;

is equivalent to

$var1 = &GLOBALS['var1'];

But if you then redefine it to be a reference to some other variable, it’s no longer a reference to the $GLOBALS element, so it’s not a global variable any more.

See the documentation References with global and static variables

If you want $var1 to retain its value, make it a global variable, but don’t make it a reference to $varDatabase. Just do

$var1 = $varDatabase;