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LIS651 lecture 3 taming PHP Thomas Krichel 2007-04-15
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LIS651 lecture 3
taming PHP
Thomas Krichel
2007-04-15
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 likeYou 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
parenthesisfunction rubino_print ($number, $singular,$plural) {
if($number == 1) {
print "one $singular";
}
else {
print "$number $plural";
}
}
rubino_print(3,'woman','women'); // prints: “3 women”
default arguments
• Sometimes you want to allow a function to be called without giving all its arguments. You can do this by declaring a default value, using an equal sign in the function listfunction thomas_need($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 $order\n";
// prints: you ordered 2 beers.
utility function for database queriesfunction mysql_fetch_all($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 $GLOBAL['name'] where name is the name of the global variable.function yankeefy ($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.
http://openlib.org/home/krichel
Thank you for your attention!
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