PHP Reusing Code and Writing Functions

1. PHP Reusing Code and Writing Functions

2. Reusing Code. Functions. • Topics: • Code inclusion using require() and include() • Defining functions • Managing function parameters • Passing-by-reference vs. passing-by-value • Parameters default values • Variable-length parameter lists • Understanding variable scope in functions • Using functions to return values • Using recursive functions • Anonymous functions

3. Reusing Code - why? • Advantages: • Reduces costs • Reusing eliminates time spent to design, code, test, debug a new piece of software. • Increases reliability • Existing, mature code is usually more reliable than new code: it has already been thoroughly tested, possible defects have been discovered during testing (and use), and have been fixed. • Improves consistency • Existing code is already consistent with the other parts of the system: in terms of user interfaces, interfaces with other systems.

4. Modularity - why? • … has a favorable impact on program development: • Allows program to be divided into logical pieces: • Level of difficulty grows with the size and complexity of a program • Divide work among programmers • Easier to debug when modules are tested alone fully first, then integrated systematically • Easier to read, especially when commented correctly. • Easier to modify, isolating modules to change • Allows for reuse (avoiding redundant code); when an algorithm or computation is done over and over, it can be put in a method.

5. Code Inclusion • PHP allows to reuse any type of code (not only functions, classes): Can insert code from a file into your PHP script with include (‘filename’); require (‘filename’); • Statements include() & require() are similar, except when they fail: • include() construct just gives a warning if failing to include file • require() construct gives a fatal error, that will cause program to terminate • Can also use variations include_once() or require_once() to avoid problems with redundancy; ex. redefining same function • Slower than include()/require()

6. Fail_include.php • http://www.nku.edu/~frank/csc301/Examples/PHP_Functions/fail_include_php.pdf • http://www.nku.edu/~frank/csc301/Examples/PHP_Functions/fail_include.php

7. Code Inclusion • The files loaded using include / require can contain everything that is normally used in a PHP file: PHP statements, PHP functions, PHP classes, HTML code, client-side scripting • PHP code still has to be placed within PHP tags • Filename extensions: • When include()/require() is used in a PHP script: the loaded file becomes part of the PHP script and is executed as such → as if the loaded file’s contents replaced the include()/require() statement • PHP does not look at the filename extension of an included file •  include files can have any extension, if not to be used directly. • Usually: .php or .inc (note: if located in the web document tree, their content can be seen in clear!)

8. Main.php • http://www.nku.edu/~frank/csc301/Examples/PHP_Functions/main_php.pdf • http://www.nku.edu/~frank/csc301/Examples/PHP_Functions/reusable_php.pdf • http://www.nku.edu/~frank/csc301/Examples/PHP_Functions/main.php

9. Home.html • http://www.nku.edu/~frank/csc301/Examples/PHP_Functions/home.html • http://www.nku.edu/~frank/csc301/Examples/PHP_Functions/home.php • http://www.nku.edu/~frank/csc301/Examples/PHP_Functions/home_php.pdf • http://www.nku.edu/~frank/csc301/Examples/PHP_Functions/header_php.pdf • http://www.nku.edu/~frank/csc301/Examples/PHP_Functions/footer_php.pdf

10. Code Inclusion • The include files can be dynamic and generate on-the-fly parts of the page • Apache or PHP can be configured to automatically load specific pages / files before and after every page, even for individual directories (applications) •  include() statements not needed in this case • Not on cscdb…