PHP says variable doesn't exist - even though it does - php

Question

The following code gives me the following error, even thought the variable 'cache_path' has been defined at the top.
<b>Notice</b>: Undefined variable: cache_path in <b>C:\Users\Jan Gieseler\Desktop\janBSite\Scripts\Index.php</b> on line <b>20</b><br />
Here is the code;
header('Content-type: application/x-javascript');
$cache_path = 'cache.txt';
function getScriptsInDirectory(){
$array = Array();
$scripts_in_directory = scandir('.');
foreach ($scripts_in_directory as $script_name) {
if (preg_match('/(.+)\.js/', $script_name))
{
array_push($array, $script_name);
}
}
return $array;
}
function compilingRequired(){
if (file_exists($cache_path))
{
$cache_time = filemtime($cache_path);
$files = getScriptsInDirectory();
foreach ($files as $script_name) {
if(filemtime($script_name) > $cache_time)
{
return true;
}
}
return false;
}
return true;
}
if (compilingRequired())
{
}
else
{
}
?>
What could I do to fix this?
EDIT: I've thought that PHP makes variables which are in the 'main' scope available for functions, too. I guess, I was wrong. Thanks for the help.
I've fixed it by using the 'global' statement.

Answer 1

In order to fully understand this you will have to read up on Variable Scope, good luck!
header('Content-type: application/x-javascript');
$cache_path = 'cache.txt';
function getScriptsInDirectory(){
$array = Array();
$scripts_in_directory = scandir('.');
foreach ($scripts_in_directory as $script_name) {
if (preg_match('/(.+)\.js/', $script_name))
{
array_push($array, $script_name);
}
}
return $array;
}
function compilingRequired($cache_path){ //<-- secret sauce
if (file_exists($cache_path))
{
$cache_time = filemtime($cache_path);
$files = getScriptsInDirectory();
foreach ($files as $script_name) {
if(filemtime($script_name) > $cache_time)
{
return true;
}
}
return false;
}
return true;
}
if (compilingRequired($cache_path)) //<-- additional secret sauce
{
}
else
{
}
?>

Answer 2

Your $cache_path is not known inside functions. Either give it as a parameter like MonkeyZeus suggests or use a global $cache_path inside your function.
function compilingRequired(){
global $cache_path; // <------- like this
if (file_exists($cache_path))
{
$cache_time = filemtime($cache_path);
$files = getScriptsInDirectory();
foreach ($files as $script_name) {
if(filemtime($script_name) > $cache_time)
{
return true;
}
}
return false;
}
return true;
}