Question

I am doing a tutorial on PHP. I am in the update section of the CRUD lesson and am working on a validation script. I have followed the code exactly… I think but still not working correctly. Here is the problem: When I click submit to try to test the validation with the menu name field empty it goes through without an error… and updates the nav with an empty list item? I have looked over the code and all seems to be correct but I am very new to this so problems are easily overlooked.

Here is the code:

if(isset($_POST['submit'])) {
    $errors = array();

    $required_fields = array('menu_name', 'position', 'visible');   
    foreach($required_fields as $fieldname) {
        if(!isset($_POST[$fieldname]) || (empty($_POST[$fieldname]) && $_POST[$fieldname] != 0) ) {
            $errors[] = $fieldname;
        }
    }

    if(empty($errors)) {
        //Perform Update
        $id = mysql_prep($_GET['subj']);
        $menu_name = mysql_prep($_POST['menu_name']);
        $position = mysql_prep($_POST['position']);
        $visible = mysql_prep($_POST['visible']);

        $query = "UPDATE subjects SET
                    menu_name = '{$menu_name}',
                    position = {$position},
                    visible = {$visible} WHERE id = {$id}";

        $result = mysql_query($query, $connection);

        if(mysql_affected_rows() == 1){
            // success
            $message = "Subject was sucessfully updated"; 
        }else{
            $message = "The subject update failed.";
            $message .= "<br />" . mysql_error();
        }
    }else{
        //error occured
        $message = "There were " . count($errors) . " errors in the form.";
    }
} // end if(isset($_POST['submit']) )
?>

And the code from the body:

<h2>Edit Subject: <?php echo $sel_subject['menu_name']; ?></h2>
<?php 
    if(!empty($message)){
        echo "<p class=\"message\">" . $message . "</p>";
    }
?>
<?php
    if(!empty($errors)){
        echo "<p class=\"errors\">";
        echo "Please review the folowing fields: <br />";
        foreach($errors as $error){
            echo "-" . $error . "</p>";
        }
    }
?>

Now when I change (empty($_POST[$fieldname]) to (empty($_POST[‘menu_name’]) it spits out errors but they are for the position and visible fields which happen to be correct…? Is there a character left out that I just cannot see. I have done mostly copy and paste to prevent those stupid kind of mistakes.. Note: that the validation for position and visible do work… I think… since you cannot leave those fields blank anyway how would I know…

Any help is greatly appreciated.

Answer 1

The error is right here:

$_POST[$fieldname] != 0

An empty string = 0 because 0 is false. So in your if statement, you say if it is empty (which it is) AND NOT equal to 0 (which it does).

What you can do is

1. Drop the !=0 statement completely as empty will do a grand job checking that.
2. Use the correct operator: !==”0″, if you want to accept “0” as an option.

When you use 3 equals or !== it validates against the type. 0===0, and 0==false, “0”==0, “0”==false, and false===false, BUT 0!==false, 0!==”0″ and “0”!==false.
I hope that makes sense.

EDIT

Lets run this down into the ground a little further with a series of tests.

$a='';
$b="0";
if(empty($a))
    echo'$a is empty<br/>';
if(empty($b))
    echo'$b is empty<br/>';
if($a!=0)
    echo'$a does not equal 0/false<br/>';
if($b!=0)
    echo'$b does not equal 0/false<br/>';
if($a!==0)
    echo'$a does not equal integer 0<br/>';
if($b!==0)
    echo'$b does not equal integer 0<br/>';
if($a!=="0")
    echo'$a does not equal string 0<br/>';
if($b!=="0")
    echo'$b does not equal string 0<br/>';

The output above would be

$a is empty
$b is empty
$a does not equal integer 0
$b does not equal integer 0
$a does not equal string 0

Conclusions: $a==$b, $a!==$b. $a AND $b are == to 0 and == to false, neither of them are integers, both are strings, and an empty string is not the same as a string containing the 0 character.

Change $_POST[$fieldname]!=0 to $_POST[$fieldname]!=="0"