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With the database designed and out of the way, it's time to actually start writing some code. First up, the user login process, and the scripts which verify the user's password and grant him access to the system.

Here's the initial login form, "index.html".

<table border="0" cellspacing="5" cellpadding="5">
<form action="login.php" method="post">
<td><input type="Text" name="frmuser" size="15"></td>
<td><input type="password" name="frmpass" size="15"></td>
<td colspan="2" align="CENTER"><input type="Submit" name="submit" value="Enter"></td>

Here's what it looks like:

Output image

Once the form is submitted, the data is processed by "login.php", which connects to the database to verify the username and password against the "users" table.

// login.php - verifies user login

// includes

// check login and password
// connect and execute query
$connection = mysql_connect($hostname, $user, $pass) or die ("Unable to connect!");
$query = "SELECT uid, uperms from users WHERE uname = '$frmuser' AND upass = PASSWORD('$frmpass')";
$result = mysql_db_query($database, $query, $connection) or die ("Error in query: $query. " . mysql_error());

// if row exists - login/pass is correct
if (mysql_num_rows($result) == 1)
   // initiate a session

   // register the user's ID and permission level
   list($uid, $uperms) = mysql_fetch_row($result);
   $SESSION_UID = $uid;
   $SESSION_UPERMS = $uperms;

   // redirect to main menu page
   mysql_free_result ($result);  

   // close connection
   // login/pass check failed
   mysql_free_result ($result);  
   // redirect to error page
   header("Location: error.php?ec=0");

Assuming the username and password is correct, the script initiates a session, and registers two session variables, $SESSION_UID (which contains the user's ID) and $SESSION_UPERMS (which contains the user's permission level). These variables will remain available throughout the session, and will be used in many of the subsequent scripts. The script then redirects the browser to "menu.php", which sets up the main menu for the system, via an HTTP header.

A login failure will redirect the browser to the generic error handler, "error.php", with an error code indicating the type of error. I'll be using this error handler extensively, to handle the different types of errors possible.

It is important to note that calls to header() and session_start() must take place before *any* output is sent to the browser. Even something as minor as whitespace or a carriage return outside the PHP tags can cause these calls to barf all over your script.

Finally, the include()d files, "config.php" and "functions.php", contain variables and functions which will be used throughout the application. The most important of these are the database name, user name and password, which are stored in "config.php" - take a look:

// config.php - useful variables/functions

// database parameters
// alter this as per your configuration
$user = "time_agent";
$pass = "gs645kaf";
$hostname = "localhost";

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