PHP-03-Functions.ppt

PHP Functions / Modularity
Dr. Charles Severance
www.wa4e.com

Why Functions?
• PHP has lots of built-in functions that we use all the
time.
• We write our own functions when our code reaches a
certain level of complexity.

To function or not to function...
• Organize your code into “paragraphs” - capture a complete
thought and “name it”.
• Don’t repeat yourself - make it work once and then reuse it.
• If something gets too long or complex, break up logical
chunks and put those chunks in functions.
• Make a library of common stuff that you do over and over -
perhaps share this with your friends...

Built-In Functions...
• Much of the power of PHP comes from its built-in functions.
• Many are modeled after C string library functions (i.e.
strlen()).
echo strrev(" .dlrow olleH"); echo
str_repeat("Hip ", 2); echo
strtoupper("hooray!");
echo strlen("intro");
echo "n";
Hello world.
Hip Hip
HOORAY!
5

Defining Your Own Functions
We use the function keyword to define a function, we name the
function and take optional argument variables. The body of the
function is in a block of code { }
function greet() {
print "Hellon";
}
greet();
greet();
Hello
Hello

Choosing Function Names
• Much like variable names - but do not start with a dollar sign
• Start with a letter or underscore - consist of letters, numbers,
and underscores ( _ )
• Avoid built-in function names
• Case does not matter – but please do not take advantage of
this

Return Values
Often a function will take its arguments, do some computation,
and return a value to be used as the value of the function call in
the calling expression. The return keyword is used for this.
function greeting() {
return "Hello";
}
print greeting() . " Glennn";
print greeting() . " Sallyn";
Hello Glenn
Hello Sally

Arguments
Functions can choose to accept optional arguments. Within the
function definition the variable names are effectively “aliases” to the
values passed in when the function is called.
function howdy($lang) {
if ( $lang == 'es' ) return "Hola";
if ( $lang == 'fr' ) return "Bonjour";
return "Hello";
}
print howdy('es') . " Glennn";
print howdy('fr') . " Sallyn";
Hola Glenn
Bonjour Sally

Optional Arguments
Arguments can have defaults, and so can be omitted.
function howdy($lang='es') {
if ( $lang == 'es' ) return "Hola";
if ( $lang == 'fr' ) return "Bonjour";
return "Hello";
}
print howdy() . " Glennn";
print howdy('fr') . " Sallyn";
Hola Glenn
Bonjour Sally

Call By Value
• The argument variable within the function is an “alias” to the
actual variable.
• But even further, the alias is to a *copy* of the actual variable
in the function call.
function double($alias) {
$alias = $alias * 2;
return $alias;
}
$val = 10;
$dval = double($val);
echo "Value = $val Doubled = $dvaln";
Value = 10 Doubled = 20

Call By Reference
Sometimes we want a function to change one of its arguments,
so we indicate that an argument is “by reference” using ( & ).
function triple(&$realthing) {
$realthing = $realthing * 3;
}
$val = 10;
triple($val);
echo "Triple = $valn";
Triple = 30

http://php.net/manual/en/function.sort.php

Variable Scope
• In general, variable names used inside of function code do
not mix with the variables outside of the function to avoid
unexpected side effects if two programmers use the same
variable name in different parts of the code.
• We call this “name spacing” the variables. The function
variables are in one “name space” whilst the main variables
are in another “name space”.
http://php.net/manual/en/language.variables.scope.php

Normal Scope (isolated)
function tryzap() {
$val = 100;
}
$val = 10;
tryzap();
echo "TryZap = $valn";
TryZap = 10
http://php.net/manual/en/language.variables.superglobals.php
Except for $_GET

Global Scope (shared)
function dozap() {
global $val;
$val = 100;
}
$val = 10;
dozap();
echo "DoZap = $valn";
DoZap = 100
Use this wisely, young
Jedi...

Global Variables – Use Rarely
• Passing variable in as parameter
• Passing value back as return value
• Passing variable in by reference
• If you use global variables, use long names with nice
unique prefixes
global $LastOAuthBodyBaseString;
global $LAST_OAUTH_BODY_BASE_STRING;

Coping with Missing Bits
Sometimes, depending on the version or configuration of a
particular PHP instance, some functions may be missing. We can
check that...
if (function_exists("array_combine")){
echo "Function exists";
} else {
echo "Function does not exist";
}
This allows for evolution.

http://php.net/manual/en/function.array-key-exists.php

One Heck of a Function…
• PHP is a very configurable system and has lots of capabilities
that can be plugged in.
• The phpinfo() function prints out the internal configuration
capabilities of your particular PHP installation,
<?php
phpinfo();
?>

Including Files in PHP
• include "header.php"; - Pull the file in here
• include_once "header.php"; - Pull the file in here unless it
has already been pulled in before
• require "header.php"; - Pull in the file here and die if it is
missing
• require_once "header.php"; - You can guess what this
means...
• These can look like functions - require_once("header.php");

https://github.com/csev/wa4e
http://www.wa4e.com/

<?php
require "top.php";
require "nav.php";
?>
<div id="container">
<h1>Web Applications...</h1>
.
.
.
</div>
<?php
require "foot.php";
index.php

<?php
require "top.php";
require "nav.php";
?>
<div id="container">
<iframeheight="4600" width="100%" frameborder="0"
marginwidth="0"marginheight="0" scrolling="auto"src="software.php">
</iframe>
</div>
<?php
require "foot.php";
install.php

Summary
• Built-in functions
• Making new functions
• Arguments - pass by value and pass by reference
• Including and requiring files
• Checking to see if functions are present

Acknowledgements / Contributions
These slides are Copyright 2010- Charles R. Severance
(www.dr-chuck.com) as part of www.wa4e.com and made
available under a Creative Commons Attribution 4.0 License.
Please maintain this last slide in all copies of the document to
comply with the attribution requirements of the license. If
you make a change, feel free to add your name and
organization to the list of contributors on this page as you
republish the materials.
Initial Development: Charles Severance, University of Michigan
School of Information
Insert new Contributors and Translators here including names
and dates
Continue new Contributors and Translators here

PHP-03-Functions.ppt

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