Please I need help to understand this code

[chris17]

I have this code in my application for form validation. it is working fine but i just copied and applied it in my work, i don't really understand how  it works. This is it:

 

$required_fields = array('menu_name', 'position', 'visible');
foreach($required_fields as $fieldname) {
    if(!isset($_POST[$fieldname]) || empty($_POST[$fieldname]) && ($_POST[$fieldname] != 0)){
        $error[] = $fieldname;
        }
    }
if(!empty($error)){
    redirect_to("new_subject.php");
    }    
//Field Length
$fields_with_lengths = array('menu_name' => 30);
foreach($fields_with_lengths as $fieldname => $maxlength){
    if(strlen(trim(mysql_prep($_POST[$fieldname]))) > $maxlength){
        $error[] = $fieldname;
        }
    }

[Ch0cu3r]

It loops through the list of field names in the $required_fields array and If they don't exist in the $_POST array or their values is empty it's add the field to the $error array

 

It then validates the field value lengths. It uses the field name as the key and the maximum string length as the value in the $fields_with_length array. It then loops though that array and sets the field to $error if the field length exceeds the string length assigned to it. For example if the field named menu_name has a string length of 30 or more then that field will be added to the $error array.

[dalecosp]

Looks like it's just some sort of POST field validator:

//create an array
$required_fields = array('menu_name', 'position', 'visible');
 
//loop through it; it appears we'll be checking to see what was POSTed from a web form.
foreach($required_fields as $fieldname) {
 
    //if the field is not set in POST, or the field is set but empty and non-zero ... I *think*.  This line actually looks rather suspicious.
    if(!isset($_POST[$fieldname]) || empty($_POST[$fieldname]) && ($_POST[$fieldname] != 0)){
        $error[] = $fieldname;   //there's an error, so we're recording which field it was in
     }
}//end foreach loop
if(!empty($error)){ // we have something in the $error array, so we'll redirect?
    redirect_to("new_subject.php");  // this must be a custom function, as no such call exists in PHP AFAIK.
    }    
 
//Now it appears we'll do the same thing, just checking one field, "menu_name" and making sure it's less than 30 characters.
//Field Length
$fields_with_lengths = array('menu_name' => 30);
foreach($fields_with_lengths as $fieldname => $maxlength){
    if(strlen(trim(mysql_prep($_POST[$fieldname]))) > $maxlength){ 
        $error[] = $fieldname;
     }
 }