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How can i create a function that takes un-assigned variable in PHP
//we have this array
$array  = array();
isset($array["test"]);//this one is valid
myFunc($array["test"]);//this one is not valid

function myFunc(&$val)
{
    return isset($val);
}

var_dump(myFunc($undefined));

<?php
function defArrayElem(&$array, $key, $default=null) {
    if(!isset($array[$key])) {$array[$key]=$default;}
}

//repeat for all the $_GET/$_POST vars you expect...
defArrayElem($_GET,'keyname','default-value');
?>