Using a function to initialise a variable if it not set - PHP - php

Question

Upon executing a script, sometimes the variable will be set, and sometimes it won't. The times that it isn't, I'm given a notice that the variable is not defined.
In efforts to clear the notice, I simple added the following code
if(!isset($var)) {
$var = NULL;
}
That works just as needed because it tests if the variable isn't already set so that we don't set something that we need to NULL. But in a file where there are over 60 variables that are of this case and more to come, I thought creating a simple function to do so would be easier. So I started with this:
function init($var) {
if(!isset($var)) {
return $var = NULL;
}
}
Obviously that doesn't work and is also riddled with errors that will annoy most programmers out there (such as the !isset() inside a function, not supplying a return statement in case the if statement is false, etc.) but that's just to give you the basic jist of what I need so in the code I can just call init($var); to test if the variable isn't already set, and then creates one and sets it to NULL to avoid the notice.
Is this even possible? To use a function to test if a variable is already set outside of the function? Thanks in advance :)

Answer 1

You can't use a function to check if a variable exists without it being initialized in the process of passing it to the function as an argument. You can, however, define an array of variable names your script requires then loop through them and check if they exist one by one. Such as:
foreach(array('username','userid','userrole','posts','dob','friends') as $var)
{
if(!isset($$var))$$var=NULL;
}
Edit: Simplifying user4035's approach, you could get the function down to:
<?php
function init(&$var){}
init($myVariable);
var_dump($myVariable);
Or even avoid a function altogether:
<?php
array(&$var1,&$var2,&$var3);//define several variables in one shot as NULL if not already defined.
var_dump($var1);
var_dump($var2);
var_dump($var3);
Another approach would be to use extract:
<?php
$defaults=array('username'=>NULL,'userid'=>0,'userrole'=>'guest','posts'=>0,'dob'=>0,'friends'=>array());
$userid=24334;
$username='bob';
$friends=array(2,5,7);
extract($defaults, EXTR_SKIP);
echo '<pre>';
print_r(
array(
'userid'=>$userid,
'username'=>$username,
'friends'=>$friends,
'userrole'=>$userrole,
'posts'=>$posts,
'dob'=>$dob)
);
echo '</pre>';
Another approach would be to temporarily disable error reporting:
<?php
$v=ini_get("error_reporting");
error_reporting(0);
echo 'One';
echo $doh;//Use an undefined variable
echo ' Two';
error_reporting($v);
I'd advise against this approach though because it is just hiding the errors rather than fixing them and will also hide errors worthy of your attention.
And my personal favorite would be to take advantage of namespaces.
Usually you'd put these into separate files but I put them into a single snippet for your convenience:
<?php
namespace //This is the global namespace
{
$config=array('production'=>0);
}
namespace MyScript
{
//Initialize all variables for our script
//anything not defined here will be inherited from the global namespace
$username=NULL;
$userid=NULL;
$userrole=NULL;
$posts=NULL;
$dob=NULL;
$friends=NULL;
}
namespace MyScript\Main
{
//Define only two variables for our script
//Everything else will be inherited from the parent namespace if not defined
$username='Ultimater';
$userid=4;
echo '<pre>';
print_r(
array(
'userid'=>$userid,
'username'=>$username,
'friends'=>$friends,
'userrole'=>$userrole,
'posts'=>$posts,
'dob'=>$dob,
'config'=>$config)
);
echo '</pre>';
}

Answer 2

If your intention is this:
if(variable is not set)
set variable to NULL
then it's quite easy to implement, using a reference:
function init(&$var) {
if(!isset($var)) {
$var = NULL;
}
}
Testing:
<?php
error_reporting(E_ALL);
function init(&$var) {
if(!isset($var)) {
$var = NULL;
}
}
init($x);
var_dump($x);
Output:
NULL