This function checks if the index of the inputArray exists and if the input is valid. The function can be called as `sanitizeInput($fieldName,$_POST,['input',$fieldName],$flags)` and equals `sanitize($fieldName,$_POST['input'][$fieldName],$flags)`, but checks first, if the index exists.
Signature
public function sanitizeInput(string
$field,
array&
$inputArray,
array
$inputKeys,
[integer
$flags = 0] )