PHP: Libraries

Derek Bridge

Department of Computer Science,
University College Cork

PHP: Libraries

Aims:

to learn how to build and use a library of useful PHP functions
to review the advantages of using functions and libraries of functions

Headers and footers

Suppose you have a huge web site and every page in your site has the same header and footer
- same DOCTYPE, similar head/title/link elements, same skiplink, same logo/banner, same permanent navigation,…
- same copyright notice, same links to legal disclaimers/ conditions of use/ privacy notices,…
That's a lot of duplication
Class exercise: Why is that a problem?

Example of simple header and footer

Simple header

<!DOCTYPE html>
<html lang="en">
    <head>
        <meta charset="utf-8" />
        <title>...</title>
        <link rel="stylesheet" href="…" />
    </head>

    <body>
        <h1>…</h1>

Simple footer

        <footer>
            <small>
                &copy; 2013 National University of Nerdland
            </small>
        </footer>
    </body>
	
</html>

Functions for headers and footers

We could define functions to output the header and footer
- See next slide for output_header
- Class exercise: Define output_footer
Put these function definitions in a separate file called, e.g., output_functions.php
Each web page in our web site is changed as follows:
- it is no longer a static web page (.html)
- it is now a dynamic web page (.php)
- it switches into interpret mode and uses the PHP command require_once to load the file of functions
- at some point (early), it switches into interpret mode and invokes the output_header function
- at some point (late), it switches into interpret mode and invokes the output_footer function

Definition of a simple `output_header` function

function output_header( $title, $stylesheet )
{
    echo 
        '<!DOCTYPE html>
         <html lang="en">
         <head>
         <meta charset="utf-8" />';
    echo "<title>{$title}</title>";
    echo "<link rel=\"stylesheet\" href=\"{$stylesheet}\" />";
    echo 
        '</head>
         <body>';
    echo "<h1>{$title}</h1>";
}

Example of a typical web page, e.g. `alchemy.php`

<?php
    require_once('output_functions.php');
    output_header( 'Department of Alchemy', 'nerdland.css' );
?>

    <p>
        Welcome to the Department of Alchemy at the National University 
        of Nerdland! We're great, we are.
    </p>
    
<?php
    output_footer( 'National University of Nerdland' );
?>

Libraries

We could add lots more useful functions for outputting common HTML elements into the output_functions.php file to turn it into a useful 'library'
- E.g. we could include output_paragraph (see earlier lecture)
- E.g. we could include output_submit_button to echo submit buttons for when the programmer is producing a form (see next slide)
- Class exercise: Define output_reset_button that will echo reset buttons
- Class exercise: Define output_textfield that will echo text fields. Your function could have the following prototype:
  void output_textfield( $id, $label, $name, $size, $maxlength, $value, $is_disabled )
- Others, e.g.: output_unordered_list,…

Definition of an `output_submit_button` function

function output_submit_button( $button_label ) 
{
    echo "<input type=\"submit\" name=\"submit\" value=\"{$button_label}\" />";
}

This is `pockets.php`, the new version of `pockets.html`

<?php
    require_once('output_functions.php');
    output_header( "What's in your pocket?", 'pockets.css' );
?>

    <form action="process.php" method="get">
<?php
    output_textfield('firstname', 'Firstname: ', 'firstname', 25, 25, '', false);
    output_textfield('surname', 'Surname: ', 'surname', 25, 25, '', false);
    output_textfield('num_1c_coins', 'One cents: ', 'num_1c_coins', 3, 3, '0', false); 
    output_textfield('num_2c_coins', 'Two cents: ', 'num_2c_coins', 3, 3, '0', false);
    …
    output_textfield('num_50e_notes', 'Fifty euros: ', 'num_50e_notes', 3, 3, '0', false);
    output_submit_button('Compute');
    output_reset_button('CLEAR');
?>
    </form>
    
<?php
    output_footer('University College Cork');
?>

Libraries

We could have other libraries (files) that contain useful functions for
- validating user data (see later lectures)
- making database connections (see later lectures)
- performing user authentication (login, logout, etc.)
- …

Advantages of functions and libraries

Easier programming
- coincides with the idea of breaking a problem down into more easily-solvable subproblems
Greater readability
- detail is encapsulated within well-named functions
- the whole script may now be shorter (less repetition)
Greater maintainability
- due to greater readability
- with less repetition, less risk of inconsistent changes
Greater testability
- each function can be independently tested and debugged
- with less repetition, less code to test
Greater re-usability
- by using libraries, the above advantages are spread across many programs that you write
- by using libraries, you have building blocks, so you can avoid 'reinventing the wheel'

Pointers for advanced students

Lookup the keywords include, include_once and require as alternatives to require_once

PHP: Libraries

Derek Bridge

Department of Computer Science, University College Cork

PHP: Libraries

Headers and footers

Example of simple header and footer

Functions for headers and footers

Definition of a simple output_header function

Example of a typical web page, e.g. alchemy.php

Libraries

Definition of an output_submit_button function

This is pockets.php, the new version of pockets.html

Libraries

Advantages of functions and libraries

Pointers for advanced students

Department of Computer Science,
University College Cork

Definition of a simple `output_header` function

Example of a typical web page, e.g. `alchemy.php`

Definition of an `output_submit_button` function

This is `pockets.php`, the new version of `pockets.html`