Strange validation error for form - php

Question

The error i got was:
Notice: Undefined index: visible in C:\xampp\htdocs\introducingphp\includes\validation_function.php on line 22
It should not happen since i already instantiated all the variables including visible
Validation_function.php
<?php
$errors = array();
function fieldname_as_text($fieldname) {
$fieldname = str_replace("_", " ", $fieldname);
$fieldname = ucfirst($fieldname);
return $fieldname;
}
// * presence
// use trim() so empty spaces don't count
// use === to avoid false positives
// empty() would consider "0" to be empty
function has_presence($value) {
return isset($value) && $value !== "";
}
function validate_presences($required_fields) {
global $errors;
foreach($required_fields as $field) {
$value = trim($_POST[$field]);
if (!has_presence($value)) {
$errors[$field] = fieldname_as_text($field) . " can't be blank";
}
}
}
// * string length
// max length
function has_max_length($value, $max) {
return strlen($value) <= $max;
}
function validate_max_lengths($fields_with_max_lengths) {
global $errors;
// Expects an assoc. array
foreach($fields_with_max_lengths as $field => $max) {
$value = trim($_POST[$field]);
if (!has_max_length($value, $max)) {
$errors[$field] = fieldname_as_text($field) . " is too long";
}
}
}
// * inclusion in a set
function has_inclusion_in($value, $set) {
return in_array($value, $set);
}
?>
new_page.php (the page that has the one-page submit form that does validation)
<?php require_once("includes/session.php"); ?>
<?php require_once("includes/db_connection.php"); ?>
<?php require_once("includes/functions.php"); ?>
<?php require_once("includes/validation_function.php"); ?>
<?php find_selected_page(); ?>
<?php
// Can't add a new page unless there is a subject as a parent
if (!$current_subject) {
// subject ID was missing or invalid or
//subject couldn't be found in database
redirect_to("manage_content.php");
}
?>
<?php
if (isset($_POST['submit'])) {
// Process the form
//validations
$required_fields = array("menu_name", "position", "visible",
"content");
validate_presences($required_fields);
$fields_with_max_lengths = array("menu_name" => 60);
validate_max_lengths($fields_with_max_lengths);
if (empty($errors)) {
// perform Create
//add the subject_id
$subject_id = $current_subject["id"];
$menu_name = mysql_prep($_POST["menu_name"]);
$position = (int) $_POST["position"];
$visible = (int) $_POST["visible"];
//escape content
$content = mysql_prep($_POST["content"]);
// 2. Perform database query
$query .= "INSERT INTO pages (";
$query .= " subject_id, menu_name, position, visible,
content";
$query .= ") VALUES (";
$query .= " {$subject_id}, '{$menu_name}', {$position},
{$visible}, '{$content}'";
$query .= ")";
$result = mysqli_query($connection, $query);
if ($result ) {
// Success
$_SESSION["message"] = "Page Created.";
redirect_to("manage_content.php?subject=" .
urlencode($current_subject["id"]));
}else {
// Failure
$_SESSION["message"] = "Page creation failed.";
}
}
} else {
// This is probably a GET request
} // End: If(isset($_POST['submit']))
?>
<?php $layout_context = "admin"; ?>
<?php include("header.php"); ?>
<div id="main">
<div id="navigation">
<?php echo navigation($current_subject, $current_page); ?>
</div>
<div id="page">
<?php echo message(); ?>
<?php echo form_errors($errors); ?>
<h2>Create Page</h2>
<form action="new_page.php?subject=<?php echo
urlencode($current_subject["id"]); ?>" method="post">
<p>Menu name:
<input type="text" name="menu_name" value="" />
</p>
<p>Position:
<select name="position">
<?php
$page_set =
find_all_pages_for_subject($current_subject["id"], false);
$page_count = mysqli_num_rows($page_set);
for($count=1; $count <= ($page_count + 1); $count++) {
echo "<option value=\"{$count}\">{$count}</option>";
}
?>
</select>
</p>
<p>Visible
<input type="radio" name="visible" value="0" /> NO
<input type="radio" name="visible" value="1" /> Yes
</p>
<p>Content:<br />
<textarea name="content" rows="20" cols="80"></textarea>
</p>
<input type="submit" name="submit" value="Create Page" />
</form>
<br />
<a href="manage_content.php?subject=<?php echo
urlencode($current_subject["id"]); ?>">Cancel</a>
</div>
</div>
<?php include("includes/footer.php"); ?>

Answer 1

You probably have a typo on the input HTML field. You can use:
if (isset($_POST[$field])) {
on validate_presences() function to be sure that the value exists.

Answer 2

When you try to do trim($_POST[$field]); you assume, the field exists in the $_POST array - for visible it does not in this case. You could move the trim to has_presence()
function has_presence($value) {
return isset($value) && trim($value) !== "";
}
function validate_presences($required_fields) {
global $errors;
foreach($required_fields as $field) {
if (!has_presence($value)) {
$errors[$field] = fieldname_as_text($field) . " can't be blank";
}
}
}
Now when you will only have the trim if the variable exists.

Answer 3

Okay, marking the radio check button makes it work now. Thanks for all your inputs guys. It has helped me a great deal.