A Programmer’s Introduction to PHP 4.0 phần 8 pps

• Simple template #1: embedding PHP in HTML • Simple template #2: using INCLUDE files to separate components • Advanced templating through the complete division of design and code • The

// will be substituted into the file contents, taking the place // of the corresponding variable

Expanding the Template Class

Of course, this template class is rather limited, although it does the trick nicely for

projects that need to be created in a hurry The nice thing about using an

object-oriented implementation strategy is that you can easily add functionality without

worrying about potentially “breaking” existing code For example, suppose you

wanted to create a method that retrieved values from a database for later

tem-plate substitution Although slightly more complicated than the file_parser()

method, which just substitutes globally-accessible variable values, an SQL-based

file parser can be written with just a few lines and encapsulated in its own

method In fact, I create one of these parsers in the address book project at the

conclusion of this chapter

Templates

Several modifications could be made to this template class, the first likelybeing the consolidation of register_file() and register_variables() This wouldautomatically add the variables in each registered file Of course, you will alsowant to insert error-checking functionality to ensure that invalid file and variablenames are not registered.

You are also likely to begin thinking about how this system could beenhanced Consider the following enhancement questions How would you create

a method that worked with entire arrays? Included Files? I think that you’ll find iteasier than it first seems As a reference, check out the implementation I createdfor an SQL-parser in the address book project at the end of this chapter You caneasily transform this general methodology into whatever implementation youdesire

This basic templating strategy has been implemented in several languagesand is certainly not a new concept Therefore, you can find a wealth of informa-tion on the Web pertaining to template implementations Two particularly inter-esting resources are this set of related articles, written with JavaScript in mind:

• http://developer.netscape.com/viewsource/long_ssjs/long_ssjs.html

• http://developer.netscape.com/viewsource/schroder_template/schroder_template.html

The following article touches upon templates as it applies to Java ServerPages:

• http://www-4.ibm.com/software/webservers/appserv/doc/guide/asgdwp.html

There are also quite a few PHP implementations that follow this templatingstrategy Several of the more interesting ones include:

• PHPLib Base Library (http://phplib.netuse.de)

• Richard Heyes’s Template Class (http://www.heyes-computing.net)

• Fast Template (http://www.thewebmasters.net/php/)The PHP resource site PHPBuilder (http://www.phpbuilder.com) also contains

a few interesting tutorials regarding template manipulation Also check out PHPClasses Repository (http://phpclasses.UpperDesign.com) Several similar tem-plating implementations are there

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Drawbacks to This Templating System

While this form of templating fulfills its purpose of completely separating the

code from the design, it is not without its disadvantages I’ll highlight these

disad-vantages here

Resulting Unfounded Belief in “Silver Bullet” Solution

While templates can aid in clearly defining the boundaries of a project in terms of

coding and design, they are not a substitute for communication In fact, they

won’t even operate correctly without concise communication between both

par-ties about exactly what information will be templated in the application As is the

case with any successful software project, a thorough survey of the application

specifications should always be drawn up before even one line of PHP is coded

This will greatly reduce the possibility for later miscommunication, resulting in

unexpected template parsing results

Performance Degradation

The dependence on file parsing and manipulation will cause the templating

sys-tem to suffer a loss in performance in terms of speed Exactly what the degree of

this loss is depends on a number of factors, including page size, SQL query size (if

any), and machine hardware In many cases, this loss will be negligible; however

there may be instances where it will be noticeable if it becomes necessary to

simultaneously manipulate several template files in high-traffic situations

Designer Is Still PHP-Impaired

One of the main reasons for creating this system at all lies in the fact that it could

be problematic if the designer comes into contact with the code when editing the

look and feel of the page In an ideal environment, the designer would also be a

programmer or at least know general programming concepts, such as a variable,

loop, and conditional A designer who is not privy to this information stands to

gain nothing from using templates except education in a relatively useless syntax

(the syntax used to delimit variable keywords) Therefore, regardless of what your

final verdict is on using this form of page templating, I strongly recommend

tak-ing time to begin educattak-ing the designer on the finer points of the PHP language

(or better, buy the designer a copy of this book!) This results in a win-win

situa-tion for both parties, as the designer will learn an extra skill, and in doing so,

become an even more valuable member of the team The programmer wins, as

this person will be an extra brain to pick for new programming ideas, perhaps

even a particularly valuable one, since chances are that the designer will look at

things from a different perspective than the typical programmer would

Templates

Project: Create an Address Book

Although templating systems are well suited for a variety of Web applications,they are particularly useful in datacentric applications in which formatting isimportant One such application is an address book Think about what a conven-tional (paper-based) address book looks like: each page looks exactly the same,save for perhaps a letter denoting which set of last names the particular page isreserved for The same kind of idea could apply to a Web-based address book Infact, formatting is even more important in this case, since it might be necessary toexport the data to another application in a particularly rigorous format This kind

of application works great with the templating system, since the designer is left tocreate a single page format that will be used for all 26 letters of the alphabet

To begin, you must decide what kind of data you want to store in the addressbook and how this data is to be stored Of course, the most plausible choice for astorage media would be a database, since this also facilitates useful features such

as searching and ordering data I’ll use a MySQL database to store the addressinformation The table looks like this:

mysql>CREATE table addressbook (

last_name char(35) NOT NULL, first_name char(20) NOT NULL, tel char(20) NOT NULL, email char(55) NOT NULL );

Of course, you can add street address, city, and state columns I’ll use thisabbreviated table for sake of illustration

Next, I’ll play the role of designer and create the templates For this project,two templates are required The first template, shown in Listing 12-8, could beconsidered the “parent” template

Listing 12-8: Parent address book template, entitled “book.html”

<table cellpadding=2 cellspacing=2 width=600>

<h1>Address Book: {letter}</h1>

<tr><td>

<a href="index.php?letter=a">A</a> | <a href="index.php?letter=b">B</a> |

<a href="index.php?letter=c">C</a> | <a href="index.php?letter=d">D</a> |

<a href="index.php?letter=e">E</a> | <a href="index.php?letter=f">F</a> |

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<a href="index.php?letter=g">G</a> | <a href="index.php?letter=h">H</a> |

<a href="index.php?letter=i">I</a> | <a href="index.php?letter=j">J</a> |

<a href="index.php?letter=k">K</a> | <a href="index.php?letter=l">L</a> |

<a href="index.php?letter=m">M</a> | <a href="index.php?letter=n">N</a> |

<a href="index.php?letter=o">O</a> | <a href="index.php?letter=p">P</a> |

<a href="index.php?letter=q">Q</a> | <a href="index.php?letter=r">R</a> |

<a href="index.php?letter=s">S</a> | <a href="index.php?letter=t">T</a> |

<a href="index.php?letter=u">U</a> | <a href="index.php?letter=v">V</a> |

<a href="index.php?letter=w">W</a> | <a href="index.php?letter=x">X</a> |

<a href="index.php?letter=y">Y</a> | <a href="index.php?letter=z">Z</a>

As you can see, the bulk of this file is given to the links displaying each letter

of the alphabet Clicking a particular letter, the user will be presented with all

per-sons stored in the address book having a last name beginning with that letter

There are also three delimited variable names: page_title, letter, androws.addresses The purpose of the first two variables should be obvious: the title

of the page and the letter of the address book currently used to retrieve address

information, respectively The third variable refers to the child template and is

used to specify which table configuration file should be inserted into the parent I

say “table configuration file” because, in a complex page, you might be

simultane-ously using several templates, each employing HTML tables for formatting data

Therefore, “rows” specifies that a table template will be inserted, and “addresses”

tells us that it is the table used to format addresses

The second template, shown in Listing 12-9, is the “child” template, because

it will be embedded in the parent Why this is necessary will soon become clear

Listing 12-9: Child address book template, entitled “rows.addresses”

There are four delimited variable names in Listing 12-9: last_name,first_name, telephone, and email The meanings of each should be obvious It isimportant to notice that this file only contains table row (<tr>…</tr>) and tablecell (<td>…</td>) tags This is because this file will be repeatedly inserted into thetemplate, one time for each address retrieved from the database Since therows.addressesvariable name is enclosed in table tags in Listing 12-8, the HTMLformatting will parse correctly To illustrate how this works, take a look at Figure12-1, which is essentially a screenshot of the completed address book in address.Then examine Listing 12-10, which contains the source code for that screen shot.You’ll see that the rows.addresses file is used repeatedly in the source code.

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Figure 12-1 Screenshot of the address book in action

Listing 12-10: Source code for Figure 12-1

href="index.php?letter=l">L</a> | <a href="index.php?letter=m">M</a> | <a

href="index.php?letter=n">N</a> | <a href="index.php?letter=o">O</a> | <a

href="index.php?letter=p">P</a> | <a href="index.php?letter=q">Q</a> | <a

href="index.php?letter=r">R</a> | <a href="index.php?letter=s">S</a> | <a

href="index.php?letter=t">T</a> | <a href="index.php?letter=u">U</a> | <a

href="index.php?letter=v">V</a> | <a href="index.php?letter=w">W</a> | <a

href="index.php?letter=x">X</a> | <a href="index.php?letter=y">Y</a> | <a

As you can see, there are apparently two persons having a last name that

begins with F stored in the address book, Bobby Fries and Pierre Frenchy

There-fore, two table rows have been inserted in the table

The design process for the address book project is complete Now, I’ll don thehat of a coder You’ll be surprised to know that there are no changes to the tem-

plate.classfile in Listing 12-7, save for one new method, address_sql() This

method is displayed in Listing 12-11

Templates

Listing 12-11: SQL parsing method, address_sql()

class template { VAR $files = array();

VAR $variables = array();

VAR $sql = array();

VAR $opening_escape = '{';

VAR $closing_escape = '}';

VAR $host = "localhost";

VAR $user = "root";

VAR $pswd = "";

VAR $db = "book";

VAR $address_table = "addressbook";

function address_sql($file_id, $variable_name, $letter) { // Connect to MySQL server and select database

mysql_connect($this->host, $this->user, $this->pswd)

or die("Couldn't connect to MySQL server!");

mysql_select_db($this->db) or die("Couldn't select MySQL database!"); // Query database

$query = "SELECT last_name, first_name, tel, email

FROM $this->address_table WHERE last_name LIKE '$letter%'";

$result = mysql_query($query);

// Open "rows.addresses" file and read contents into variable.

$fh = fopen("$variable_name", "r");

$file_contents = fread($fh, filesize("rows.addresses") );

// Perform replacements of delimited variable names with table data while ($row = mysql_fetch_array($result)) :

} // end template.class

The comments in Listing 12-11 should suffice for understanding themechanics of what is taking place However, there are still a few important points

to make First, notice that the rows.addresses file is opened only once An

alterna-tive way to code this method would be to repeatedly open and close the

rows.addresses file, replacing information each time and appending it to the

$complete_tablevariable However, this would be highly inefficient coding

prac-tice Therefore, take some time to review how the loop is used to continuously

append new table information to the $complete_table variable

Templates

A second point to make about Listing 12-11 is that five new class attributesare used: $host, $user, $pswd, $db, and $address_table Each of these pertains toinformation that the MySQL server requires, and the meaning of each should beobvious If it isn’t obvious, take a moment to read through Chapter 11, “Data-bases.”

All that’s left to do now is code the file that triggers the template parsing Thisfile is shown in Listing 12-12 By clicking one of the letter links

(index.php?letter=someletter) in book.html (Listing 12-8), this file will be called,

in turn regenerating the book.html file with appropriate information

Listing 12-12: Template parser index.php

<?

include("template.class");

$page_title = "Address Book";

// The default page will retrieve persons having last name beginning with 'a'

effi-What’s Next?

This chapter introduced a particularly useful concept of both PHP and Web gramming in general: advanced template usage It began with a synopsis of thetwo templating systems covered thus far, simple variable substitution via PHPembedding, and the use of INCLUDE files to separate page components I thenintroduced the third and most advanced template strategy, which completelyseparates the code from the design of the page The remainder of the chapter was

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spent examining a class built to implement this type of template, concluding with

a practical implementation of the template system, using a Web-based address

book as an example This example also built on the simple template class,

imple-menting an SQL parser

In particular, the following topics were discussed in this chapter:

• Why templates?

• Simple template #1: embedding PHP in HTML

• Simple template #2: using INCLUDE files to separate components

• Advanced templating through the complete division of design and code

• The template class

• File registration

• Variable registration

• File parsing

• File printing

• Disadvantages to using templates

• Address book project that expands on the default class, implementing anSQL parser

Next chapter, I continue the discussion of dynamic Web application ment, introducing how cookies and session tracking can add a new degree of user

develop-interactivity to your Web site!

Templates

C H A P T E R 1 3 Cookies and Session

Tracking

The ability to track users and customize user information based on personal

pref-erences has become both one of the hottest and most debated features to be

offered on the Web While the advantages of being able to offer users services

based on exactly what they desire are obvious, many questions have been raised

regarding privacy in terms of the ramifications of being able to “follow” a user as

that user navigates from page to page, and even from site to site

Barring privacy concerns, the process of tracking user information throughcookies or other technologies can be immensely beneficial to both the user and

the site offering these services It is to the user’s benefit that these services provide

the opportunity to customize content, weeding out any information that may be

uninteresting or useless This capability is also highly beneficial to the site

admin-istrators, as tracking user preferences and habits opens up a whole new realm of

possibilities for user interaction, including targeted marketing and a vastly

supe-rior analysis of the popularity of their onsite content On the

commerce-domi-nated Web, these capabilities are by now practically the de facto standard

This idea of tracking a user while navigating through your site can be defined

as session tracking Given the vast amount of knowledge that could be gained

from introducing session tracking into your site architecture, it could be said that

the advantages of session tracking and providing customized content far

out-weigh the disadvantages With that said, this could hardly be considered a

com-plete PHP textbook without devoting a chapter to PHP’s session-tracking

capabili-ties In this chapter, I introduce several concepts closely intertwined with session

tracking, namely, session cookies and their uses, unique session identification

numbers, before concluding the chapter with a synopsis of PHP’s predefined

ses-sion-tracking configuration and predefined functions

What Is a Cookie?

A cookie is nothing more than a small parcel of information that is sent by a Web

server and stored on a client browser This can be advantageous to the developer

because useful data regarding the user session can be stored and then later

retrieved, resulting in the creation of a state of persistence between the client and

server Cookies are commonly used by many Internet sites as a means to enhanceboth user experience and site efficiency, providing a way to track user navigation,actions, and preferences The ability to store this information is a key feature forsites offering such services as online shopping, site personalization, and targetedadvertising.

Due to the usercentric purpose of cookie usage, the key piece of informationstored is likely to be a unique user identification number (UIN) This ID is subse-quently stored in a database and is used as the key for retrieving any informationstored in the database that is mapped to this UIN Of course, it is not mandatorythat the cookie is used to store a UIN; you could store anything you like in thecookie, provided that its total size does not surpass four kilobytes (4096 bytes)

Cookie Components

Interestingly, other pieces of information are also stored in the cookie, enablingthe developer to tailor its usage in terms of domain, time frame, path, and secu-rity Here are descriptions of the various cookie components:

• name—The cookie name is a mandatory parameter because the name is

the parameter from which the cookie is referenced The cookie name can

be essentially thought of in terms of a variable name

• value—A cookie value is simply a piece of data mapped to the cookie name.

This could be a user identification number, background color, date, thing

any-• expiration date—This date defines the lifetime of the cookie Once this

timestamp equals the current date and time, the cookie will expire and berendered unusable According to cookie specifications, inclusion of theexpiration date is optional However, PHP’s cookie-setting functionalityrequires that this expiration date is set According to the cookie specifica-tions, if an expiration date is not included, the cookie will expire at the end

of the user session (that is, when the user exits the site)

• domain—This is the domain that both created and can read the cookie

If a domain has multiple servers and would like all servers to be able to access the same cookie, then the domain could be set in the form of phprecipes.com In this case all potential third-level domains falling underthe PHPrecipes site, such as wap.phprecipes.com or news.phprecipes.com,would have access to the cookie For security reasons, a cookie cannot beset for any domain other than the one mapped to the server attempting to

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set the cookie This parameter is optional If it is not included, it will default

to the domain name from which the cookie is emanating

• path—The path setting specifies the URL path from which the cookie is

valid Any attempt to retrieve a cookie from outside of this path will fail

Setting path is optional If it is not set, then the path will be set to the path

of the document from which the cookie is created

• security—This determines whether or not the cookie can be retrieved in a

nonsecure setting Because the cookie will be primarily used in a nonsecuresetting, this optional parameter will default to FALSE

Although all cookies must abide by the same set of syntax rules when they areset, the cookie storage format is browser dependent For example, Netscape Com-

municator stores a cookie in a format similar to the following:

.phprecipes.com FALSE / FALSE 971728956 bgcolor blue

In Internet Explorer, the same cookie would be stored as:

newline character found at the end of each line, causing them to appear as

squares in the cookie document

Cookies and Session Tracking

NOTE Internet Explorer stores its cookie information in a folder aptly tled “Cookies,” while Netscape Communicator stores it in a single file enti- tled “cookies.” Just perform a search on your drive to find these files.

If you took a moment to read the introduction to cookies, you are alreadyfamiliar with the parameters in the setcookie() syntax If you’ve skipped aheadand are not familiar with the mechanics of persistent cookies, I suggest that youreturn to the beginning of this section and read through the introduction, as all ofthe setcookie() parameters are introduced there.

Before proceeding, I ask that you read the following sentence not once, not

twice, but three times A cookie must be set before any other page-relevant

infor-mation is sent to the browser Write this 500 times on a blackboard, get a tattoostating this rule, teach your parrot to say it: I don’t care, just get it straight In otherwords, you cannot just set a cookie where you wish in a Web page It must be sent

before any browser-relevant information is sent; otherwise it will not work.

Another important restriction to keep in mind is that you cannot set a cookieand then expect to use that cookie in the same page Either the user must refreshthe page (don’t count on it), or you will have to wait until the next page requestbefore that cookie variable can be used

This example illustrates how setcookie() is used to set a cookie containing auser identification number:

• This cookie is only accessible via the phprecipes.com domain.

• This cookie is accessible via a nonsecured protocol

The next example, shown in Listing 13-1, illustrates how a cookie can be used

to store page-formatting preferences, in this case the background color Notice

how the cookie will only be set if the form action has been executed.

Listing 13-1: Storing a user’s favorite background color

<form action="<? print $PHP_SELF; ?>" method="post">

What's your favorite background color?

page will be set to the value specified by the variable $bgcolor Otherwise, an

Cookies and Session Tracking

HTML form will appear, prompting the user to specify a favorite backgroundcolor Once the color is specified, subsequent reloading of the page or traversal toany page using the cookie value $bgcolor will be recognized.

Interestingly, you can also use array notation to specify cookie names Youcould specify cookie names as uid[1], uid[2], uid[3], and so on, and then lateraccess these values just as you would a normal array Check out Listing 13-2 for anexample of how this works

Listing 13-2: Assigning cookie names according to array index value

<?

setcookie("phprecipes[uid]", "4139b31b7bab052", time()+3600);

setcookie("phprecipes[color]", "black", time()+3600);

setcookie("phprecipes[preference]", "english", time()+3600);

if (isset ($phprecipes)) { while (list ($name, $value) = each ($phprecipes)) { echo "$name = $value<br>\n";

} }

?>

Executing this script results in the following output, in addition to three cookiesbeing set on the user’s computer:

uid = 4139b31b7bab052 color = black

preference = english

Perhaps the most common use of cookies is for storage of a user tion number that will be later used for retrieving user-specific information Thisprocess is illustrated in the next listing, where a UIN is stored in a MySQL data-base The stored information is subsequently retrieved and used to set variouspieces of information regarding the formatting of the page

identifica-To set the stage for the next listing, assume that a table entitled user_inforesides on a database named user The user_info table contains three pieces of

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NOTE Although the use of array-based cookies may seem like a great idea for storing all kinds of information, keep in mind that certain browsers (such as Netscape Communicator) limit the number of cookies to 20 per domain.

information: a user ID, first name, and email address This table was created using

the following syntax:

mysql>create table user_info (

com-name, and email address) has already been inserted into the database To

elimi-nate the need for the user to later log in, the user ID (set to 15 in Listing 13-3 for

the sake of illustration) is stored on the user’s computer by way of a cookie

Listing 13-3: Retrieving user information from a database

<?

if (! isset($userid)) :

$id = "15";

setcookie ("userid", $id, time()+3600);

print "A cookie containing your userID has been set on your machine Please refresh the page to retrieve your user information";

else:

@mysql_connect("localhost", "web", "4tf9zzzf")

or die("Could not connect to MySQL server!");

@mysql_select_db("user") or die("Could not select user database!");

print "Hi ".$row["fname"].",<br>";

print "Your email address is ".$row["email"];

mysql_close();

endif;

?>

Listing 13-3 highlights just how useful cookies can be for identifying users

The above scenario could be applied to any number of situations, ranging from

eliminating the need to log in to effectively tracking user preferences

Cookies and Session Tracking

The listing in the next section, “Unique Identification Numbers,” illustratesthe complete process of user registration and subsequent storage of the uniqueuser ID.

Unique Identification Numbers

By now you are probably curious just how easy it is to create a unique UIN Putyour college calculus books away; there is no need for funky 17th-century algo-rithms PHP provides an easy way to create a unique UIN through its predefinedfunction uniqid()

The function uniqid() generates a 13-character unique identification ber based on the current time Its syntax is:

num-int uniqid (string prefix [, boolean lcg])

The input parameter prefix can be used to begin the UIN with a particular stringvalue Since prefix is a required parameter, you must designate at least an emptyvalue If set to TRUE, the optional input parameter lcg will cause uniqid() to pro-duce a 23-character UIN To quickly create a unique ID, just call uniqid() using anempty value as the sole input parameter:

$uniq_id = uniqid("");

// Some 13 character value such as ' 39b3209ce8ef2' will be generated.

Another way to create a unique ID is to prepend the derived value with astring, specified in the input parameter prefix, as shown here:

$uniq_id = uniqid("php", TRUE);

// Some 16 character value such as 'php39b3209ce8ef2' will be generated.

Given the fact that uniqid() creates its UIN based on the current time of thesystem, there is a remote possibility that it could be guessed Therefore, you maywant to ensure that its value is truly random by first randomly choosing a prefixusing another of PHP’s predefined functions, rand() The following exampledemonstrates this usage:

srand ((double) microtime() * 1000000);

Chap-The function srand() acts to initiate the random number generator If youwant to ensure that rand() consistently produces a random number, you must

execute srand() first Placing rand() as an input parameter to uniqid() will result

in rand() first being executed, returning a prefix value to uniqid(), which will

then execute, producing a UIN that would be rather difficult to guess

Armed with the knowledge of how to create unique user IDs, you can nowcreate a practical user registration scheme On first request of the script in Listing

13-4, the user is greeted with a short form requesting a name and email address

This information will be then inserted along with a generated unique ID into the

table user_info, first described along with Listing 13-3 A cookie containing this

unique ID is then stored on the user’s computer Any subsequent visit to the page

will prompt the script to query the database based on the unique user ID stored

in the cookie, displaying the user information to the screen

Listing 13-4: A complete user registration process

<?

// build form

$form = "

<form action=\"Listing13-4.php\" method=\"post\">

<input type=\"hidden\" name=\"seenform\" value=\"y\">

Your first name?:<br>

<input type=\"text\" name=\"fname\" size=\"20\" maxlength=\"20\" value=\"\"><br>

Your email?:<br>

<input type=\"text\" name=\"email\" size=\"20\" maxlength=\"35\" value=\"\"><br>

<input type=\"submit\" value=\"Register!\">

</form>

";

// If the form has not been displayed and the user does not have a cookie.

if ((! isset ($seenform)) && (! isset ($userid))) :

print $form;

// If the form has been displayed but the user information

// has not yet been processed

elseif (isset ($seenform) && (! isset ($userid))) :

srand ((double) microtime() * 1000000);

$uniq_id = uniqid(rand());

// connect to the MySQL server and select the users database

@mysql_pconnect("localhost", "web", "4tf9zzzf")

or die("Could not connect to MySQL server!");

@mysql_select_db("user") or die("Could not select user database!");

Cookies and Session Tracking

// declare and execute query

$query = "INSERT INTO user_info VALUES('$uniq_id', '$fname', '$email')";

$result = mysql_query($query) or die("Could not insert user information!"); // set cookie "userid" to expire in one month.

setcookie ("userid", $uniq_id, time()+2592000);

print "Congratulations $fname! You are now registered! Your user information will be displayed on each subsequent visit to this page.";

// else if the cookie exists, use the userID to extract // information from the users database

elseif (isset($userid)) : // connect to the MySQL server and select the users database

@mysql_pconnect("localhost", "web", "4tf9zzzf")

or die("Could not connect to MySQL server!");

@mysql_select_db("user") or die("Could not select user database!");

// declare and execute query

$query = "SELECT * FROM user_info WHERE user_id = '$userid'";

$result = mysql_query($query) or die("Could not extract user information!");

$row = mysql_fetch_array($result);

print "Hi ".$row["fname"].",<br>";

print "Your email address is ".$row["email"];

endif;

?>

The judicious use of several if conditionals makes it possible to use one script

to take care of each step of the registration and subsequent user recognition cess There are three scenarios involved in this script:

pro-• The user has not seen the form and does not have a valid cookie This is thestep where the user is presented with the form

• The user has filled in the form and does not yet have a valid cookie This isthe step where the user information is entered into the database, and thecookie is set, due to expire in one month

• The user returns to the script If the cookie is still valid (has not expired),the cookie is read in and the relevant information is extracted from thedatabase

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The general process shown in Listing 13-4 could of course be applied to any

data-base This illustrates, on a very basic level, how many of the larger sites are able to

apply user-specified preferences to their site, resulting in a “tailor-made” look for

For more information regarding cookies and their usage, take a moment to read

through a few of the resources that I’ve gleaned from the Web:

user-spe-cookies can not be solely relied on since users can set their browsers to refuse to

accept cookies Thankfully, PHP offers an alternative methodology for storing

per-sistent information; This method is called session tracking and is the subject of

the next section

Session Handling

A session is best defined as the period of time beginning when a user enters your

site and ending when the user exits Throughout this session, you may wish to

assign various variables that will accompany the user while navigating around

your site, without having to manually code a bunch of hidden forms or appended

URL variables This otherwise tedious process becomes fairly easy with session

handling.

Consider the following scenario Using session handling, a user entering yoursite would be assigned a unique session id (SID) This SID is then sent to the user’s

browser in a cookie entitled PHPSESSID If cookie support is disabled or not

sup-ported, this SID can be automatically appended to all local URLs throughout the

user session At the same time, a file with the same name as the SID is stored on

Cookies and Session Tracking