PHP variables randomly becomes NULL - php

Question

For quite a while now we experience a very weird problem with our hosting server. Once a while (seems randomly) variables in PHP become NULLs.
In general everything works perfectly fine, but once a while it happens. All accounts on the server are affected and all PHP apps (including PHPMyAdmin, Wordpress our own scripts). We contacted our hosting company, but they are unable to find any solution.
I had few ideas, the most promising one was an issue with Suhosin. But I do not get any message in the log directly from it.
We made a simplest possible script to reproduce the error:
<?php
class Example
{
protected $stringVar = 'this is a string value';
public function accessParameter()
{
$error = false;
if (isset($this->stringVar) && !is_null($this->stringVar)) {
echo "string var : " . $this->toStringWithType($this->stringVar) . "\n";
} else {
echo "string var is not set\n";
$error = true;
}
if ($error) {
$logfile = dirname(__FILE__)."/random_bug_log.log";
file_put_contents($logfile, date('Y-m-d H:i:s')."\n", FILE_APPEND);
file_put_contents($logfile, $this->toStringWithType($this->stringVar) . "\n", FILE_APPEND);
}
}
public function toStringWithType($var)
{
$type = gettype($var);
return "($type) '$var'";
}
}
$e = new Example();
$e->accessParameter();
Normal output:
string var : (string) 'this is a string value'
Output when the weird thing happens:
string var is not set
I open to any ideas or suggestions how to solve this problem. I guess the ultimate solution is to change the hosting company. I did not manage to create this issue on localhost or any other server.
Test piece that have been made, including your suggestions:
<?php
class Example
{
protected $stringVar = 'this is a string value';
public function accessParameter() {
$error = false;
if(isset($this->stringVar) && !is_null($this->stringVar)) {
echo "string var : "
.$this->toStringWithType($this->stringVar)
."\n";
} else {
echo "string var is not set\n";
$error = true;
}
if($error) {
$logfile = dirname(__FILE__)."/random_bug_log.log";
file_put_contents($logfile, date('Y-m-d H:i:s')." ", FILE_APPEND);
file_put_contents($logfile,
$this->toStringWithType($this->stringVar) . "\n",
FILE_APPEND);
}
}
public function writeParameter() {
$this->stringVar="variable assigned";
if(isset($this->stringVar) && !is_null($this->stringVar)) {
echo "string var : "
.$this->toStringWithType($this->stringVar)
."\n";
} else {
echo "string var is not set\n";
$error = true;
}
}
public function toStringWithType($var)
{
$type = gettype($var);
return "($type) '$var'";
}
}
$e = new Example();
$e->accessParameter();
$e->writeParameter();
The output while the thing happens:
string var is not set
string var is not set

Answer 1

it is very strange problem.
it may not be a solution but worth to try;
protected $stringVar;
function __construct() {
$this->stringVar = 'this is a string value';
}

Answer 2

I would recommend to use !== instead of is_null to see if the variable is actually null.
if (isset($this->stringVar) && ($this->stringVar !== null)) {
or
if (isset($this->stringVar) && (!empty($this->stringVar)) {
should do the work too.

Answer 3

In case of theses type of issues check with the value that you have in if condition and do what you want in else. Like in your situation do like:
if(isset($this->stringVar) && ($this->stringVar == "this is a string value")) {
}else{
// your code here...
}