PHP Form data validation issue - php

Question

I am making a basic content management system and I have got stuck with the validation of data being entered into a form.
For example, one form is to edit the name of a subject (in the navigation menu). The form contains a few different pieces of data but the main focus is the "menu_name" field (name of subject).
On form submission data in "menu_name" should be checked to ensure it is not empty and if it is then give an error. What is happening is that the form validation doesn't seem to be working as when I enter nothing the script continues to edit the subject name, in this case making it blank.
This is the script that is executed on form submission:
if (isset($_POST['submit']))
{
// Process the form
// Validations
$required_fields = array("menu_name", "position", "visible");
validate_presences($required_fields);
$fields_with_max_lengths = array("menu_name" => 30);
validate_max_lengths($fields_with_max_lengths);
// If errors occured, redirect
if(empty($errors))
{
// Perform update
// Assign POST data to variables
$id = $current_subject["id"];
$menu_name = mysql_prep($_POST["menu_name"]);
$position = (int) $_POST["position"];
$visible = (int) $_POST["visible"];
// 2. Perform database query
$query = "UPDATE subjects SET ";
$query .= "menu_name = '{$menu_name}', ";
$query .= "position = '{$position}', ";
$query .= "visible = '{$visible}' ";
$query .= "WHERE id = {$id} ";
$query .= "LIMIT 1";
$result = mysqli_query($connection, $query);
if ($result && mysqli_affected_rows($connection) >= 0)
{
// Success
$_SESSION["message"] = "Subject updated.";
redirect_to("manage_content.php");
}
else
{
// Failure
$message = "Subject update failed.";
}
}
}
The data is then checked by two custom validation functions as you can see, the second one is not my concern but the first function validate_presences(), here is the function:
function validate_presences($requried_fields)
{
GLOBAL $errors;
foreach($required_fields as $field)
{
$value = trim($_POST[$field]);
if (!has_presence($value))
{
$errors[$field] = fieldname_as_text($field) . " can't be blank";
}
}
}
You can see there that it references the has_presence() function, which is:
function has_presence($value)
{
return isset($value) && $value !== "";
}
If anyone has any ideas on what is wrong, any help is appreciated!
Just ask if you need some more information.
Thanks in advance!

Answer 1

Why don't you just return the error array instead of making it global? I think it will resolve your problem instantly ;)
function validate_presences($requried_fields)
{
$errors = array();
foreach($required_fields as $field)
{
$value = trim($_POST[$field]);
if (!has_presence($value))
{
$errors[$field] = fieldname_as_text($field) . " can't be blank";
}
}
return $errors;
}
Now set $errors = validate_presences($required_fields); and your ready to go!

Answer 2

It's not recommended to use variables in a global way like this. Rather pass the errors variable by reference to the validation functions.
$errors = array();
function validate_presences($requried_fields, &$errors)
{
foreach($required_fields as $field)
{
$value = trim($_POST[$field]);
if (!has_presence($value))
{
$errors[$field] = fieldname_as_text($field) . " can't be blank";
}
}
}
$required_fields = array("menu_name", "position", "visible");
validate_presences($required_fields, $errors);
$fields_with_max_lengths = array("menu_name" => 30);
validate_max_lengths($fields_with_max_lengths, $errors);
// If errors occured, redirect
if(empty($errors))
{