You can use the RecursiveArrayIterator and the RecursiveIteratorIterator (to iterate over the array recursively) from the Standard PHP Library (SPL) to make this job relatively painless.
$iterator = new RecursiveIteratorIterator(new RecursiveArrayIterator($arr));
$keys = array();
foreach ($iterator as $key => $value) {
// Build long key name based on parent keys
for ($i = $iterator->getDepth() - 1; $i >= 0; $i--) {
$key = $iterator->getSubIterator($i)->key() . '_' . $key;
}
$keys[] = $key;
}
var_export($keys);
The above example outputs something like:
array (
0 => 'Student_Address_StreetAddress',
1 => 'Student_Address_StreetName',
2 => 'Student_Marks1',
3 => 'Student_Marks2',
)