PHP - Undefined variable

Question

I\'m doing some exercises from Beginners PHP & MySQL by Mr. Tucker.

On his example everything works fine, but on my PC there is an error:

Answer 1

while ($row = mysql_fetch_array($tUser_SQLselect_Query, MYSQL_ASSOC)) {
  $passwordRetrieved = $row['password'];
}

this is the only place where a value may be assigned to the variable $passwordRetrieved.
If there is no record in the result set the body of the while-loop is never executed and therefore no value ever is assigned to $passwordRetrieved and therefore $passwordRetrieved does not exist/is undefined at line 39 -> Notice: Undefined variable: passwordRetrieved in C:\wamp\www\loginForm.php on line 39.

Answer 2

You should define $passwordRetrieved before using it. This notice does not affect it at all.

To avoid this, define it:

$thisScriptName = "loginForm.php";

$passwordRetrieved;

Answer 3

That's because your query returned nothing and your

while ($row = mysql_fetch_array($tUser_SQLselect_Query, MYSQL_ASSOC)) {

didn't fill

$passwordRetrieved

You can disable E_NOTICE notices because it's not something that would hurt

Or add

$passwordRetrieved = "";

before your

while ($row = mysql_fetch_array($tUser_SQLselect_Query, MYSQL_ASSOC)) {

Answer 4

Do a check using mysql_num_rows($result) to make sure you actually got something.

Answer 5

You are trying to access the variable $passwordRetrieved when it has not yet been given a value. The access is done here:

echo "passwordRetrieved = ".$passwordRetrieved."<br />";

The variable would be set just above:

while ($row = mysql_fetch_array($tUser_SQLselect_Query, MYSQL_ASSOC)) {
    $passwordRetrieved = $row['password'];  // VARIABLE SET HERE
}

The important thing is that the variable only gets set if the query returns a matching row (i.e., on a successful login). If the login is not valid, the variable is not set.

To check if a variable is set without getting a notice, you would use either isset or empty (there are subtle differences, but as a rule of thumb you can use either most of the time). Your code actually already does this just below:

// Checking if $passwordRetrieved has been set using empty()
if (!empty($passwordRetrieved) AND ($password == $passwordRetrieved)) {

Answer 6

You simply use an undefined variable. If your while loop doesn't work your variable steel is undefined, so you obtain an error :)