LIS651 lecture 3 taming PHP

Thomas Krichel 2007-04-15 LIS651 lecture 3taming PHP

functions • The PHP function reference is available on its web site http://php.net/quickref.php. It shows the impressive array of functions within PHP. • But one of the strengths of PHP is that you can create your own functions as you please. • If you recreate one of the built-in functions, your own function will have no effect.

simplest function function beer_print { print "beer\n"; } beer_print() ; // prints: “beer” and newline

A more practical example • Stephanie Rubino was an English teacher and objects to sentences like You have ordered 1 bottles of Grosswald Pils. • Let us define a function rubino_print(). It will take three arguments • a number to check for plural or singular • a word for the singular • a word for the plural

a function and its arguments • declare the arguments to the function in parenthesis function rubino_print ($number, $singular,$plural) { if($number == 1) { print "one $singular"; } else { print "$number $plural"; } } rubino_print(3,'woman','women'); // prints: “3 women”

default arguments • Sometimes you want to allow a function to be called without giving all its arguments. You can do this by declaring a default value, using an equal sign in the function list function thomas_need($thing='beer') { print "Thomas needs $thing.\n"; } thomas_need(); // prints: “Thomas needs beer.” thomas_need('vodka'); // prints: “Thomas needs vodka”.

rubino_print using common plurals function rubino_print ($num, $sing,$plur=1) { if($num == 1) { print "one $sing"; } elseif($plur ==1) { print "$num $sing"."s"; } else { print "$num $plur"; } } rubino_print(6,'beer') // prints: “6 beers”

return value • Up until now we have just looked at the side effect of a function. • "return" is a special command that returns a value. • It takes the return value as a parameter return $result; • When return is used, the function is left. Example function good_beer () { return 'Festbock'; } $beer=good_beer; print $beer ; // prints: “Festbock”.

rubino_print with return function rubino_print ($number, $singular,$plural) { if($number == 1) { return "one $singular"; } return "$number $plural"; } $order=rubino_print(2,"beer","beers"); print "you ordered $order\n"; // prints: you ordered 2 beers.

utility function for database queries function mysql_fetch_all($query) { $r=@mysql_query($query); if($err=mysql_error()) { return $err; } if( mysql_num_rows($r) ) { while($row=mysql_fetch_array($r)) { $result[]=$row; } return $result; } }

usage example my $query="SELECT * FROM my_table"; if(is_array($rows=mysql_fetch_all($query)) { // do something } else { if (! is_null($rows)) { die("Query failed!");} }

visibility of variables • Variables used inside a function are not visible from the outside. Example $beer="Karlsberg"; function yankeefy ($name='Sam Adams') { $beer=$name; } yankeefy(); print $beer; // prints: Karlsberg • The variable inside the function is something different than the variables outside.

accessing global variables. • There are two ways to change a global variable, i.e. one that is defined in the main script. • One is just to call it as $GLOBAL['name'] wherename is the name of the global variable. function yankeefy ($name="Sam Adams"){ $GLOBALS['beer']="name"; } • The other is to change it outside a function definition. • Example in brewer_quiz.php

working with many source files • Many times it is useful to split a PHP script into several files. • PHP has two mechanisms. • require(file) requires the to be included. If the file is not there, PHP exits with an error. • include(file) includes the file.

require() and include() • Both assume that you leave PHP. Thus within your included file you can write simple HTML. • If you want to include PHP in your included file, you have to surround it by <?php and ?>, just like in a PHP script. • Here is an example to use include to build the basic web page.

top.html <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> <html> <head><title>$title</title> <meta http-equiv="content-type" content="text/html; charset=UTF-8"/> <link rel="stylesheet" type="text/css" href="main.css"/> </head> <body>

bottom.html <p id="validator"> <a href="http://validator.w3.org/check?uri=referer"><img style="border: 0pt" src="http://wotan.liu.edu/valid-xhtml10.png" alt="Valid XHTML 1.0!" height="31" width="88" /></a> </p> </body> </html>

validated.php <?php $title="my basic page\n"; include("top.html"); print "<div>hello, world</div>"; include("bottom.html"); ?>

trouble • $title in the top.html is not understood as the title. It reads as $title, which means "idiot" for your web user. • Even if you replace $title with <?php $title ?> $title is empty. The definition from the outer file is not seen in the included file. • So you have to split into three files, and print the title in the main file. I leave that to you to figure out.

login.php & create_account.php • Both require a database that has three fields • id which is an auto_increment int acting as a handle • username is the username of the account. it must be unique and this is enforced by mySQL • password is a varchar(41) because the sha1 of the password is stored. This is 40 chars long.

sessions • You will recall that HTTP is a stateless protocol. Each request/response is self-contained. • Statefulness is crucial in Web applications. Otherwise users have to authenticate every time they access a new page. • Traditionally, one way to create statefulness is to use cookies. • PHP uses cookies to create a concept of its own, sessions, that makes it all very easy.

cookies • A cookie is a piece of attribute/value data. A server can send cookies as value of a HTTP header Set-Cookie:. Multiple headers may be sent. • When the client visits the web site again, it will send the cookie back to the server with a HTTP header Cookie:

Set-Cookie • Set-Cookie: name=value; [expires= date;] [path=path;] [domain= domain] [secure] • where • name= is the variable name set in the cookie • value= is the variable's value • date= is a date when the cookie expires • path= restricts the cookie to be sent only when requests to a path starting with path are made • domain= restricts the sending of the cookie to a certain domain • secure restricts transmission to https

Cookies: • The browser compares the request it wants to make with the URL and the domain that sent the cookie. • If the path is not set the cookie will only be sent to a request with the originating URL. • If the cookie matches the request a request header of the form Cookie: name1=value1 ; name2=value2 is sent.

sessions • Sessions are a feature of PHP. PHP remembers a session through a special cookie PHPSESSID. • To activate the sessions, include session_start(); at the beginning of your script, before any printing has been done. • One a session is active, you have a special super-global variable $_SESSION. Session data is stored in special files on wotan.

$_SESSION • This is an array where you can read and set variables that you want to keep during the session. if($_SESSION[user_name]) { print "welcome $_SESSION[user_name]"; } else { // show users login form print login_form(); }

ending sessions • At 9 and 39 past each hour, wotan deletes all session files that have not been changed for 24 minutes or more. • If you want to remove a session yourself, you can call session_destroy() in your script. • An example is in visit.php.

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LIS651 lecture 3 taming PHP