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--- eg-259:lecture18 [2008/12/01 08:20] – eechris
+++ eg-259:lecture18 [2013/03/08 18:04] (current) – [PHP for Web Applications] eechris
@@ Line 1: / Line 1: @@
+~~SLIDESHOW~~
+====== PHP for Web Applications ======
+**Supplementary Material**
+Provided for Reference. This material is no longer taught on this module.
+**Lecturer**: [[C.P.Jobling@Swansea.ac.uk|Dr Chris P. Jobling]].
+Using PHP for web applications development.
+===== PHP for Web Applications =====
+We conclude our review of the Basics of PHP with a discussion of its use in creating web applications.
+----
+Based on Chapter 12 of Robert W. Sebasta, //Programming the World-Wide Web//, 3rd Edition, Addison Wesley, 2006. and Chapter 12 of Chris Bates, //Web Programming: Building Internet Applications//, 3rd Edition, John Wiley, 2006.
+===== Contents of this Lecture =====
+//PHP for web applications with examples//
+    * [[eg-259:lecture18#queries_and_query_strings|Queries and Query Strings]]
+    * [[eg-259:lecture18#form_handling|Form Handling]]
+    * [[eg-259:lecture18#files|Files]]
+    * [[eg-259:lecture18#storing_information_about_client_state|Storing Information about Client State]]
+    * [[eg-259:lecture18#session_tracking|Session Tracking]]
+The [[eg-259:examples:php1#example_from_lecture_18|Examples for PHP for Web Applications]].
+===== Learning Outcomes ====
+//At the end of this lecture you should be able to answer these questions//:
+   - How can the value of a form element be accessed by a PHP script?
+   - What is a file variable?
+   - What is a file pointer?
+   - What does an ''fopen'' function return if it fails?
+   - Explain the parameters and actions of the ''fread'' function.
+===== Learning Outcomes (continued) =====
+//At the end of this lecture you should be able to answer these questions//:
+   - What is returned by the ''fwrite'' function?
+   - How can a cookie be created in a PHP script?
+   - How can a script determine whether a particular cookie exists?
+   - How can a variable be saved in a session?
+===== Queries and Query Strings =====
+  * Parameters sent to a Web Application from a web browser take the form of a //query string//
+  * The //query string// is either appended to the URI in a GET request as in:
+     GET /webapp.cgi?query_string HTTP/1.1
+     Host: some.host.com
+      :
+  * or is carried in the payload of a POST request as in:
+     POST /webapp.cgi HTTP/1.1
+     Host: some.host.com
+      :
+     query_string
+===== Processing GET rquests =====
+  * Web server passes two environment variables to helper application
+  * ''$REQUEST_METHOD=GET'' and ''$QUERY_STRING=query_string''
+  * The query string will be content of ''$QUERY_STRING'' (everything in resource name after query marker ''?'')
+===== A Real GET request =====
+  * //From [[http://localhost/beer_get.html|beer example]]//
+  GET /cgi-bin/echo_params.cgi?colour=light&taste=malty HTTP/1.1
+  Host: localhost
+  User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.0; en-GB; rv:1.8.1.9) Gecko/20071025 Firefox/2.0.0.9 Creative ZENcast v2.00.14
+  Accept: text/xml,application/xml,application/xhtml+xml,text/html;q=0.9,text/plain;q=0.8,image/png,*/*;q=0.5
+  Accept-Language: en-gb,en;q=0.5
+  Accept-Encoding: gzip,deflate
+  Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7
+  Keep-Alive: 300
+  Connection: keep-alive
+  Referer: http://localhost/beer_get.html
+----
+  * Web application is ''/cgi-bin/echo_params.cgi''
+  * Host is ''localhost''
+  * Query string is ''colour=light&taste=malty''
+  * Although data comes from a form (//referer// is http://localhost/beer_get.html), request is equivalent to and indistinguishable from URI: http://localhost/cgi-bin/echo_params.cgi?colour=light&taste=malty.
+===== Processing POST requests =====
+  * Data passed to helper application in //environment variables// and //standard input//
+  * ''$REQUEST_METHOD=POST''
+  * ''$CONTENT_LENGTH'' gives size of payload
+  * ''$CONTENT_TYPE'' is type of data: usually ''application/x-www-form-urlencoded''
+  * Query string is ''$CONTENT_LENGTH'' bytes read from //standard input//
+===== A Real POST request =====
+  * //Also from [[http://localhost/beer_post.html|beer example]]//
+  POST /cgi-bin/echo_params.cgi HTTP/1.1
+  Host: localhost
+  User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.0; en-GB; rv:1.8.1.9) Gecko/20071025 Firefox/2.0.0.9 Creative ZENcast v2.00.14
+  Accept: text/xml,application/xml,application/xhtml+xml,text/html;q=0.9,text/plain;q=0.8,image/png,*/*;q=0.5
+  Accept-Language: en-gb,en;q=0.5
+  Accept-Encoding: gzip,deflate
+  Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7
+  Keep-Alive: 300
+  Connection: keep-alive
+  Referer: http://localhost/beer_post.html
+  Content-Type: application/x-www-form-urlencoded
+  Content-Length: 24
+  colour=light&taste=malty
+----
+  * Web application is ''/cgi-bin/echo_params.cgi''
+  * ''Host'' is ''localhost''
+  * ''Content-Type'' is ''application/x-www-form-urlencoded''
+  * ''Content-Length'' is 24 bytes
+  * Query string is ''colour=light&taste=malty'' (is ASCII 24 bytes in length)
+===== Query String Format =====
+    * A query string includes names and values of HTML form elements (widgets)
+    * Widget values are always coded as strings
+    * The form of a name/value pair in a query string is:
+      name=value
+    * If the form has more than one widget, their values are separated with ampersands:
+      milk=2&payment=visa
+===== URL Specification =====
+  * The specification for URLs ([[http://www.rfc-editor.org/rfc/rfc1738.txt|RFC 1738]], Dec. '94) limits the use of allowed characters in URLs to only a limited subset of the US-ASCII character set:
+> "...Only alphanumerics ''[0-9a-zA-Z]'', the special characters "''$-_.+!*'(),''" , and reserved characters used for their reserved purposes may be used unencoded within a URL."
+  * Any source of general text that appears in an HTML page that may be represented in a URL has to be encoded to ensure that illegal characters do not appear.
+  * This includes widget names, and widget values.
+===== URL Encoding =====
+    * Performed automatically by Browser on form submission
+    * Each special character is encoded as a percent sign and a two-character hexadecimal number (the ASCII code for the character)
+    * Some browsers code spaces as plus signs, rather than as ''%20''
+    * You should URL encode any text that will be sent to the browser in a form widget, or in the ''action'', ''src'', ''href'', etc.
+----
+For more more information on URL encoding see ((Brian Wilson, URL Encoding (or: 'What are the "%20" codes in URLs?'), Index DOT Html, URL: http://www.blooberry.com/indexdot/html/topics/urlencoding.htm))
+===== URL Encoding – Examples =====
+  * URL encode general text (e.g. from file input or results of a previous form submission)
+<code php>
+  <?php
+    echo '<a href="mycgi?foo=', urlencode($userinput), '">';
+  ?>
+</code>
+  * URL encode user input, then convert results into valid HTML (e.g. & -> &amp;)
+<code php>
+  <?php
+    $query_string = 'foo=' . urlencode($foo) . '&bar=' . urlencode($bar);
+    echo '<a href="mycgi?' . htmlentities($query_string) . '">';
+  ?>
+</code>
+===== PHP and Query Data =====
+    * PHP takes care of extracting the query parameters for you
+    * It maps the HTTP request fields into PHP variables
+    * It extracts the query string from the HTTP request, extracts the name/value pairs and places them into an array.
+    * Array ''$_GET'' will contain data for GET method and ''$_POST'' will contain data passed by the POST method
+       * value subscripts are the widget names
+    * This is transparent and it does not matter whether GET or POST method is used to transmit the form data
+===== Query parameters =====
+    * If the query string has ''colour=light&taste=malty''
+    * ''$_POST["colour"]'' will return ''"light"'' and ''$_POST["taste"]'' will return ''"malty"''
+    * Query matching will also turn check box group ''colour=red&colour=blue'' to an array so that ''$_POST["colour"]'' returns the right thing.
+===== Form Handling =====
+    * Simple in PHP
+    * Forms could be handled by the same document that creates the form, but that may be confusing
+    * Better to separate "view" from data handling
+===== Example – Popcorn Sales =====
+   * //The Form Page (just HTML)// : [[/~eechris/eg-259/examples/lecture18/popcorn3.html|popcorn3.html]] ( [[http://localhost/eg-259/examples/lecture18/popcorn3.html|popcorn3.html @ localhost]] )
+<html>
+    <form action = "popcorn3.php"
+    method = "post">
+      <h2> Welcome to Millennium Gymnastics Booster Club Popcorn
+      Sales </h2>
+      <table>
+        <!-- Text widgets for the customer's name and address -->
+        <tr>
+          <td> Buyer's Name: </td>
+          <td>
+          <input type = "text" name = "name"
+          size = "30" required placeholder="Your name"/>
+          </td>
+        </tr>
+        <tr>
+          <td> Street Address: </td>
+          <td>
+          <input type = "text" name = "street"
+          size = "30" required placeholder = "Street"/>
+          </td>
+        </tr>
+        <tr>
+          <td> City, State, Zip: </td>
+          <td>
+          <input type = "text" name = "city"
+          size = "30" required placeholder="City, State, Zip"/>
+          </td>
+        </tr>
+      </table>
+      <p />
+      <table border = "border">
+        <!-- First, the column headings -->
+        <tr>
+          <th> Product </th>
+          <th> Price </th>
+          <th> Quantity </th>
+        </tr>
+        <!-- Now, the table data entries -->
+        <tr>
+          <td> Unpopped Popcorn (1 lb.) </td>
+          <td> $3.00 </td>
+          <td align = "center">
+          <input type = "number" name = "unpop"
+          size = "3" min="0" pattern="\d+" />
+          </td>
+        </tr>
+        <tr>
+          <td> Caramel Popcorn (2 lb. canister) </td>
+          <td> $3.50 </td>
+          <td align = "center">
+          <input type = "number" name = "caramel"
+          size = "3" min="0" pattern="\d+" />
+          </td>
+        </tr>
+        <tr>
+          <td> Caramel Nut Popcorn (2 lb. canister) </td>
+          <td> $4.50 </td>
+          <td align = "center">
+          <input type = "number" name = "caramelnut"
+          size = "3" min="0" pattern="\d+" />
+          </td>
+        </tr>
+        <tr>
+          <td> Toffey Nut Popcorn (2 lb. canister) </td>
+          <td> $5.00 </td>
+          <td align = "center">
+          <input type = "number" name = "toffeynut"
+          size = "3" min="0" pattern="\d" />
+          </td>
+        </tr>
+      </table>
+      <p />
+      <!-- The radio buttons for the payment method -->
+      <h3> Payment Method </h3>
+      <p>
+        <input type = "radio" name = "payment" value = "visa"
+        checked = "checked" />
+        Visa
+        <br />
+        <input type = "radio" name = "payment" value = "mc" />
+        Master Card
+        <br />
+        <input type = "radio" name = "payment"
+        value = "discover" />
+        Discover
+        <br />
+        <input type = "radio" name = "payment" value = "check" />
+        Check
+        <br />
+        <br />
+        <!-- The submit and reset buttons -->
+        <input type = "submit" value = "Submit Order" />
+        <input type = "reset" value = "Clear Order Form" />
+      </p>
+    </form>
+</html>
+----
+<code html>
+<!DOCTYPE html>
+<!-- popcorn3.html - This describes the popcorn sales form -->
+<html lang="en">
+  <head>
+    <meta charset="utf-8" />
+    <title> Popcorn Sales - for PHP handling </title>
+  </head>
+  <body>
+    <form action = "popcorn3.php"
+    method = "post">
+      <h2> Welcome to Millennium Gymnastics Booster Club Popcorn
+      Sales </h2>
+      <table>
+        <!-- Text widgets for the customer's name and address -->
+        <tr>
+          <td> Buyer's Name: </td>
+          <td>
+          <input type = "text" name = "name"
+          size = "30" required placeholder="Your name"/>
+          </td>
+        </tr>
+        <tr>
+          <td> Street Address: </td>
+          <td>
+          <input type = "text" name = "street"
+          size = "30" required placeholder = "Street"/>
+          </td>
+        </tr>
+        <tr>
+          <td> City, State, Zip: </td>
+          <td>
+          <input type = "text" name = "city"
+          size = "30" required placeholder="City, State, Zip"/>
+          </td>
+        </tr>
+      </table>
+      <p />
+      <table border = "border">
+        <!-- First, the column headings -->
+        <tr>
+          <th> Product </th>
+          <th> Price </th>
+          <th> Quantity </th>
+        </tr>
+        <!-- Now, the table data entries -->
+        <tr>
+          <td> Unpopped Popcorn (1 lb.) </td>
+          <td> $3.00 </td>
+          <td align = "center">
+          <input type = "number" name = "unpop"
+          size = "3" min="0" pattern="\d+" />
+          </td>
+        </tr>
+        <tr>
+          <td> Caramel Popcorn (2 lb. canister) </td>
+          <td> $3.50 </td>
+          <td align = "center">
+          <input type = "number" name = "caramel"
+          size = "3" min="0" pattern="\d+" />
+          </td>
+        </tr>
+        <tr>
+          <td> Caramel Nut Popcorn (2 lb. canister) </td>
+          <td> $4.50 </td>
+          <td align = "center">
+          <input type = "number" name = "caramelnut"
+          size = "3" min="0" pattern="\d+" />
+          </td>
+        </tr>
+        <tr>
+          <td> Toffey Nut Popcorn (2 lb. canister) </td>
+          <td> $5.00 </td>
+          <td align = "center">
+          <input type = "number" name = "toffeynut"
+          size = "3" min="0" pattern="\d" />
+          </td>
+        </tr>
+      </table>
+      <p />
+      <!-- The radio buttons for the payment method -->
+      <h3> Payment Method </h3>
+      <p>
+        <input type = "radio" name = "payment" value = "visa"
+        checked = "checked" />
+        Visa
+        <br />
+        <input type = "radio" name = "payment" value = "mc" />
+        Master Card
+        <br />
+        <input type = "radio" name = "payment"
+        value = "discover" />
+        Discover
+        <br />
+        <input type = "radio" name = "payment" value = "check" />
+        Check
+        <br />
+        <br />
+        <!-- The submit and reset buttons -->
+        <input type = "submit" value = "Submit Order" />
+        <input type = "reset" value = "Clear Order Form" />
+      </p>
+    </form>
+  </body>
+</html>
+</code>
+===== Example – Popcorn Sales Receipt =====
+    * //The results page -- HTML with embedded PHP//: popcorn3.php
+----
+<code php>
+<!DOCTYPE html>
+<!-- popcorn3.php - Processes the form described in
+popcorn3.html
+-->
+<html lang="en">
+  <head>
+    <meta charset="utf-8" />
+    <title> Process the popcorn3.html form </title>
+  </head>
+  <body>
+    <?php
+// Get form data values
+$unpop=$_POST["unpop"];
+$caramel=$_POST["caramel"];
+$caramelnut=$_POST["caramelnut"];
+$toffeynut=$_POST["toffeynut"];
+$name=$_POST["name"];
+$street=$_POST["street"];
+$city=$_POST["city"];
+$payment=$_POST["payment"];
+// If any of the quantities are blank, set them to zero
+if($unpop=="")
+$unpop=0;
+if($caramel=="")
+$caramel=0;
+if($caramelnut=="")
+$caramelnut=0;
+if($toffeynut=="")
+$toffeynut=0;
+// Compute the item costs and total cost
+$unpop_cost=3.0*$unpop;
+$caramel_cost=3.5*$caramel;
+$caramelnut_cost=4.5*$caramelnut;
+$toffeynut_cost=5.0*$toffeynut;
+$total_price=$unpop_cost+$caramel_cost+$caramelnut_cost+$toffeynut_cost;
+$total_items=$unpop+$caramel+$caramelnut+$toffeynut;
+// Return the results to the browser in a table
+    ?>
+    <h4> Customer: </h4>
+    <?php
+print("$name <br /> $street <br /> $city <br />");
+    ?>
+    <p />
+    <p />
+    <table border = "border">
+      <caption>
+        Order Information
+      </caption>
+      <tr>
+        <th> Product </th>
+        <th> Unit Price </th>
+        <th> Quantity Ordered </th>
+        <th> Item Cost </th>
+      </tr>
+      <tr align = "center">
+        <td> Unpopped Popcorn </td>
+        <td> $3.00 </td>
+        <td><?php print("$unpop");?></td>
+        <td><?php printf("$ %4.2f",$unpop_cost);?></td>
+      </tr>
+      <tr align = "center">
+        <td> Caramel Popcorn </td>
+        <td> $3.50 </td>
+        <td><?php print("$caramel");?></td>
+        <td><?php printf("$ %4.2f",$caramel_cost);?></td>
+      </tr>
+      <tr align = "center">
+        <td> Caramel Nut Popcorn </td>
+        <td> $4.50 </td>
+        <td><?php print("$caramelnut");?></td>
+        <td><?php printf("$ %4.2f",$caramelnut_cost);?></td>
+      </tr>
+      <tr align = "center">
+        <td> Toffey Nut Popcorn </td>
+        <td> $5.00 </td>
+        <td><?php print("$toffeynut");?></td>
+        <td><?php printf("$ %4.2f",$toffeynut_cost);?></td>
+      </tr>
+    </table>
+    <p />
+    <p />
+    <?php
+print("You ordered $total_items popcorn items <br />");
+printf("Your total bill is: $ %5.2f <br />",$total_price);
+print("Your chosen method of payment is: $payment <br />");
+    ?>
+  </body>
+</html>
+</code>
+  * Output
+<html>
+        <h4> Customer: </h4>
+     <br />  <br />  <br />    <p /> <p />
+<table border = "border">
+      <caption> Order Information </caption>
+      <tr>
+        <th> Product </th>
+        <th> Unit Price </th>
+        <th> Quantity Ordered </th>
+        <th> Item Cost </th>
+      </tr>
+      <tr align = "center">
+        <td> Unpopped Popcorn </td>
+        <td> $3.00 </td>
+        <td> 0 </td>
+        <td> $ 0.00        </td>
+      </tr>
+      <tr align = "center">
+        <td> Caramel Popcorn </td>
+        <td> $3.50 </td>
+        <td> 0 </td>
+        <td> $ 0.00        </td>
+        </tr>
+      <tr align = "center">
+        <td> Caramel Nut Popcorn </td>
+        <td> $4.50 </td>
+        <td> 0 </td>
+        <td> $ 0.00        </td>
+      </tr>
+      <tr align = "center">
+        <td> Toffey Nut Popcorn </td>
+        <td> $5.00 </td>
+        <td> 0 </td>
+        <td> $ 0.00        </td>
+      </tr>
+    </table>
+    <p /> <p />
+    You ordered 0 popcorn items <br />Your total bill is: $  0.00 <br />Your chosen method of payment is:  <br />
+</html>
+===== Files =====
+    * PHP can:
+          * Deal with any files on the server
+          * Deal with any files on the Internet, using either HTTP or FTP
+    * Instead of filehandles, PHP associates a variable with a file, called the //file variable// (for program reference)
+    * A file has a //file pointer// (where to read or write)
+===== Opening a File =====
+    * Command to open a file and assign to a file variable:
+<code php>
+  $fptr = fopen(filename, use_indicator)
+</code>
+===== File use indicators =====
+^ Indicator ^ Purpose ^
+| ''r'' | read only, from the beginning |
+| ''r+'' | read and write, from the beginning |
+| ''w'' | write only, from the beginning (also creates the file, if necessary) |
+| ''w+'' | read and write, from the beginning (also creates the file, if necessary) |
+| ''a'' | write only, at the end, if it exists (creates the file, if necessary) |
+| ''a+'' | read and write, read at the beginning, write at the end |
+===== File opening and closing =====
+   * Because //fopen// could fail, use it with die:
+<code php>
+  $file_var = fopen("testdata.dat", "r") or
+    die ("Error - testdata.dat cannot be opened");
+</code>
+    * Use ''file_exists(filename)'' to determine whether file exists before trying to open it
+    * Use ''fclose(file_var)'' to close a file
+===== File use cases =====
+  - [[#read_all_or_part_of_the_file_into_a_string_variable|Read all or part of the file into a string variable]]
+  - [[#read_the_lines_of_the_file_into_an_array|Read the lines of the file into an array]]
+  - [[#read_one_line_from_the_file|Read one line from the file]]
+  - [[#read_one_character_at_a_time|Read one character at a time]]
+===== Read all or part of the file into a string variable =====
+<code php>
+  $str = fread(file_var, number_of_bytes)
+</code>
+  * To read the whole file, use ''filesize(file_name)'' as the second parameter
+===== Read the lines of the file into an array =====
+<code php>
+  $file_lines = file(file_name)
+</code>
+  * Need not open or close the file
+===== Read one line from the file =====
+<code php>
+  $line = fgets(file_var, number_of_bytes)
+</code>
+   * Reads characters until //eoln//, //eof//, or ''number_of_bytes'' characters have been read
+===== Read one character at a time =====
+<code php>
+  $ch = fgetc(file_var)
+</code>
+  * Control reading lines or characters with //eof// detection using ''feof'' (''TRUE'' for ''eof''; ''FALSE'' otherwise):
+<code php>
+  while( ! feof($file_var) ) {
+    $ch = fgetc($file_var);
+  }
+</code>
+===== Writing to files =====
+    * To write to a file use:
+<code php>
+  $bytes_written = fwrite(file_var, string)
+</code>
+    * ''fwrite'' returns the number of bytes it wrote
+    * Files can be locked (to avoid interference from concurrent accesses) with ''flock''((PHP Manual Page: [[http://uk3.php.net/flock|Flock]]))
+===== Storing Information about Client State =====
+    * A session is the time span during which a browser interacts with a particular server
+    * The HTTP protocol is stateless
+    * But, there are several reasons why it is useful for the server to relate a request to a session
+          * Shopping carts for many different simultaneous customers
+          * Customer profiling for advertising
+          * Customized interfaces for specific clients
+    * Approaches to storing client information:
+          * Store it on the server -- often too much to store!
+          * Store it on the client machine -- this works
+===== Session Tracking with Cookies =====
+    * A cookie is a small object of information consisting of a name and a textual value
+    * Cookies are created by some software system on the server
+    * Every HTTP communication between the browser and the server includes information in its header about the message
+    * At the time a cookie is created, it is given a lifetime
+    * Every time the browser sends a request to the server that created the cookie, while the cookie is still alive, the cookie is included
+    * A browser can be set to reject all cookies
+===== Baking Cookies =====
+    * Create a cookie with setcookie:
+<code php>
+  setcookie(cookie_name, cookie_value, lifetime)
+</code>
+    * e.g.:
+<code php>
+  setcookie("voted", "true", time() + 86400);
+</code>
+    * Cookies must be created before any other HTML is created by the script
+----
+<note>
+//Lifetime// is measured in seconds. The value 86400 is 24 hours. The PHP function ''time()'' returns the number of seconds since the "//UNIX epoch date//" [Midnight GMT, 1st January 1970]. Thus the use of ''time() + 86400'' creates a cookie that expires 24 hours from the time it was set.
+</note>
+===== Consuming Cookies =====
+    * Cookies are obtained in a script the same way form values are obtained, using the ''$_COOKIES'' array
+===== Session Tracking =====
+    * For session tracking, PHP creates and maintains a session tracking id
+    * Create the id with a call to ''session_start'' with no parameters
+    * Subsequent calls to ''session_start'' retrieves any session variables that were previously registered in the session
+===== Session Tracking =====
+    * To create a session variable, use the global array ''$_SESSION''
+===== Session Tracking: Example =====
+    * To count number of pages visited in a web site, put the following code in all documents:
+<code php>
+  <?php session_start(); // must be called before any HTML is output
+  ?>
+  :
+  <?php
+     if (!IsSet($_SESSION['page_number']))
+        $_SESSION['page_number'] = 1;
+     print("You have now visited " . $_SESSION['page_number'] . " pages <br />");
+     $_SESSION['page_number']++;
+  ?>
+</code>
+===== Summary of this Lecture =====
+//PHP for web applications with examples//
+    * [[eg-259:lecture18#queries_and_query_strings|Queries and Query Strings]]
+    * [[eg-259:lecture18#form_handling|Form Handling]]
+    * [[eg-259:lecture18#files|Files]]
+    * [[eg-259:lecture18#storing_information_about_client_state|Storing Information about Client State]]
+    * [[eg-259:lecture18#session_tracking|Session Tracking]]
+The [[eg-259:examples:php1#examples_from_lecture_18|Examples for PHP for Web Applications]].
+===== Learning Outcomes ====
+//At the end of this lecture you should be able to answer these questions//:
+   - How can the value of a form element be accessed by a PHP script?
+   - What is a file variable?
+   - What is a file pointer?
+   - What does an ''fopen'' function return if it fails?
+   - Explain the parameters and actions of the ''fread'' function.
+===== Learning Outcomes (continued) =====
+//At the end of this lecture you should be able to answer these questions//:
+   - What is returned by the ''fwrite'' function?
+   - How can a cookie be created in a PHP script?
+   - How can a script determine whether a particular cookie exists?
+   - How can a variable be saved in a session?
+===== Homework Exercise =====
+Write, test, and debug (if necessary) a PHP script for the following function. Write functions and the code to test them.
+  - //Parameter//: A file variable of a file of text, where the words are separated by spaces or colons. //Return value//: The word that appears most often in the file.
+There are more exercises [[eg-259:homework:18|here]] and in the [[eg-259:cw2|second coursework]].
+===== What's Next? =====
+**Database Access through the Web**
+  * [[eg-259:lecture19#relational_databases|Relational Databases]]
+  * [[eg-259:extras:dbandsql|Introduction to SQL]] (not examined)
+  * [[eg-259:lecture19#architectures_for_database_access|Architectures for Database Access]]
+  * [[eg-259:lecture19#the_mysql_database_system|Introducing MySQL]]
+  * [[eg-259:lecture19#database_access_with_php_mysql|Database Access with PHP and MySQL]]
+[[eg-259:lecture17|Previous Lecture]] | [[eg-259:home]] | [[eg-259:lecture19|Next Lecture]]