More Misc Topics

 

Error Handling

The following code generates an error because the file does not exist. The default error message provides too much information about how our script works.
Run Example - Generate an Error
<?php

// Do something wrong
echo "opening wrong file<br>";
$file=fopen("NoSuchFile.txt", "r");
echo "done.<br>";

?>

We can create our own error handling function, with a custom message.
Run Example - Custom Error Handler

<?php

// Create Custom Error Handler
function myErrHandler ($errNum, $errString)
  {
   echo "<b>Error Code $errNum:</b> $errString<br>";
  }
set_error_handler("myErrHandler");

// Do something wrong
echo "opening wrong file<br>";
$file=fopen("NoSuchFile.txt", "r");
echo "done.<br>";

?>

We can even have an error send us an email message.
Run Example - Error w/ Email

<?php

// Create Custom Error Handler
function myErrHandler ($errNum, $errString)
  {
   echo "Oops! We apologize for the disruption in service.<br>Please try again later.<P>";
   error_log ("Error Code $errNum: $errString",1,"dannellys@winthrop.edu","From: dannellys@winthrop.edu");
  }
set_error_handler("myErrHandler");

// Do something wrong
echo "opening wrong file<br>";
$file=fopen("NoSuchFile.txt", "r");
echo "done.<br>";

?>

Sessions

Data can be saved during session by using the predefined _SESSION variable. This is an alternative to using a cookie. Just like cookies must be dealt with before any HTML is sent to the browser, we must Start the Session before HTML is sent to the browser.

Run Example - Session Test 

<?php

// must start Session first!
session_start();

// we have been here before
if (isset($_SESSION["usrname"]))
   echo "Welcome " . $_SESSION['usrname'] . "!<br />";

// user specified name
else if (isset($_POST['usrname']))
   {
    $_SESSION ["usrname"] = $_POST['usrname'];
    echo "Setting the Session<P>";
   }

// first time visitor
else
   {
    echo "Welcome first time visitor<P>";
    echo "<form action='sess_test1.php' method='Post'>";
    echo "User Name: <input type='text' name='usrname'><br>";
    echo "<input type=submit value='Save Name'<P>";
    echo "</form>";
   }

?>
So, which is better: cookies or sessions? Obviously, the answer is "It Depends." If you want to remember a user id after the browser closes, then you must use cookies. If you want the user to be logged out as soon as they close the browser, then use session data. In terms of security, sessions have the advantage because no sensative data is stored on the client machine.

 

Other System Variables

We have used _POST, _COOKIE, and _SESSION. If we sent our form data to our script via GET instead of the POST method, then we would retrieve form data from the _GET system variable. Two other interesting system variables are _ENV and _SERVER.

Run Example - Print_R for _SERVER and _ENV

 

O b j e c t s

Process_Selection.php
<?php

require_once "Appt_Library";

// Get Info from Form
if ( !is_set ($_POST['fName'] ))
   did not supply a name
   blah blah
$fName = $_POST['fName'];
blah blah

// Create a New Appointment
$myAppt = new studentAppt();
$myAppt->setNames($fName, $lName);
$myAppt->setDayTime($day,$time);

// Remove Time Slot and Save Appt
$myAppt->deleteTimeSlot();
$myAppt->saveRecord();

?>
Appt_Library.php
class studentAppt
{
   private $fName, $lName;
   private $apptDay, $apptTime;
   
   // * * * * * * * * * * * * * * * * * * * * * * * * * *
   __construct ()
   {
      blah blah blah
   }
   __destruct ()
   {
      blah blah blah
   }
   
   // * * * * * * * * * * * * * * * * * * * * * * * * * *
   function setNames ($param1, $param2)
   {
      $this->fName = $param1;
      $this->lName = $param2;
   }
   function setDayTime ($param1, $param2)
   {
      $this->apptDay = $param1;
      $this->apptTime = $param2;
   }

   // * * * * * * * * * * * * * * * * * * * * * * * * * *
   function getDayTime()
   {
      SELECT * FROM appointments WHERE ...
      ...
      return array (this->$apptDay, this->$apptTime);
   }
   
   // * * * * * * * * * * * * * * * * * * * * * * * * * *
   function saveRecord()
   {
      INSERT INTO appointments VALUES ( $fName, $lName, $apptDay, $apptTime );
   }
   
   // * * * * * * * * * * * * * * * * * * * * * * * * * *
   function isExistingRecord()
   {
      SELECT * FROM appointments WHERE ...
      if ($record_count == 0)
         return false;
      else
         return true;
   }
   
   // * * * * * * * * * * * * * * * * * * * * * * * * * *
   function deleteTimeSlot()
   {
      DELETE FROM timeslots WHERE day=$apptDay && time=$apptTime;
   }
Find_Appt.php
require_once "Appt_Library";

. . .
process the form
. . .

// create a new appointment instance
$myAppt = new studentAppt();
$myAppt->setNames($fName, $lName);

// is that appt in the system?
if ($myAppt->isExistingRecord())
   {
    $dayTime = $myAppt->getDayTime();
    echo "Your appointment is at $dayTime[1] on $dayTime[0]";
   }
else
   {
    echo "Could NOT find your appointment.";
   }