PHP: Code Reuse & Functions

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1 Course: Internet Programming Universiteti i Prishtinës PHP: Code Reuse & Functions Prof. Assoc. Lule Ahmedi

2 Code Reuse The main motto in software engineering: Reuse, reuse, reuse, Benefits: Reduced costs: Instead of developing from the scratch, re-use existing code If commercial code, trade carefully Careful if modifications to the existing reused code required - might cost much more than writing from the scratch Reliability: Mature in-use code vs. fresh code Lines of code already existing to prevent or resolve defects Consistency: Code already proved to interact well with the external users / systems Program modularly to make code re-usable

3 include() and require() or Load a file into a PHP script statements: Similar to #include statement in C or C++ What when file cannot be included (it doesn t exist, or server doesn t permit to access it)? only a warning (E_WARNING) displayed and execution continues a fatal error (E_ERROR) displayed and execution stops

4 include_once() and require_once() & Identical to and except If file has already been included, will not be included/required again versions: Avoids loss in time in redundantly including same file(s) Protects from accidentally including same function library twice which may lead to Erroneously redefining functions & causing errors Example: functionx defined differently in included files file2 and file3 Prevents from deadlock inclusion Example: file1 includes file2, file2 includes file3, file3 includes file1,..

5 Including Files: Options Comparison Example: Let include & Let in turn include included twice within!! Use or to avoid such situations Nevertheless, if you aim to yourself avoid such situations, use or which are then faster

6 Including Files: Issues and can be deadly What if the file included contained the line: Good news: latest releases of PHP no longer support access of remote files via include Bad news: for each of functions below, PHP code inside the target file is still executed! Caution. If nonstandard extension files like (stands for files to include) used, and stored in web accessible tree: When users directly browse them => code displayed in plain text, including any passwords Therefore: Store included files outside document tree, or Configure your web server to process certain extensions like.inc (default is.php) to proceed as PHP as well

7 Include Common Code Across Site and and common elements Similar to master file in ASP.NET) useful to include templates Example: include and within ( ignores PHP code - renamed) to show same common parts of a Website across all pages In case changes required in, one single file changed to reflect all pages in the site

8 Include Common Code Across Site (cont) Use instead if file is plain text or HTML, no PHP lines Will echo file content without parsing it Important safety measure if using user-provided text Use ) & Requires configuration in like: Optionally, create & configure file to affect your directory only with: Advantage over configuration in : No need to restart the web server & no administrator access required Drawback: files are read and parsed each time a file in that directory is requested rather than just once at startup => performance penalty

9 Writing Functions in PHP User-defined functions, or built-in functions (rich PHP libraries) Format: is not case sensitive (variable names are) Convention: all lowercase; Letters, digits, _ ; But $name() also valid a variable function whose name is the value of the $name variable No parameter or return types (e.g., in C/C++ ) All variables declared inside functions are local

10 Writing Functions in PHP - Example

11 Function Parameters Multiple parameters, pass by value or pass by reference, default values # and order of parameters matters If # parameters > 1, may only leave out parameters from right

12 Functions Variable # of Parameters Three helper functions: to find out how many parameters have been passed and what their values are

13 Function Overloading! Defaults Overloaded functions Same functions with different parameters NOT supported: in PHP, signature of a function based on its name, not its parameters Method overloading within classes YES (later) Default parameter values to overcome it: Simply combine 2 overloaded functions into 1 so that if you call it with no parameter, it uses a default value Once you declare default values, all subsequent parameters must also have defaults

14 Parameters: Pass by Value Default: parameters passed by value to functions A copy of the variable passed: If the parameter modified within the function, the original does not change

15 Parameters: Pass by Reference Function may change content of a passed variable A parameter points the local variable (&) at the same If the parameter modified within the function, the original changes as well

16 Pass by Value vs. Pass by Reference

17 Namespaces An abstract container that contains functions, constants, and classes that you define Advantages of using namespaces: All functions, classes, and constants within a namespace automatically prefixed with the namespace name Unqualified class, function, and constant names are resolved at runtime, with first search taking place in the namespace before moving out to global space For more info & examples, visit:

18 PHP Built-In Functions: Strings - String length - String compare; Returns < 0 if str1 is less than str2; > 0 if str1 is greater than str2, and 0 if they are equal - Return position of character; 0 to strlen(#str) - 1, or FALSE if not found - Substring given positions, - Uppercase or lowercase entire string - Split a string by string; returns an array - Join array elements with a string; returns a string Complete list of string functions

19 PHP Built-In Functions: Arrays Complete list of string functions

20 PHP Built-In Functions: Arithmetics Returns < - Converts a string to an integer - Type casting The usual gang: () or Complete list of math functions

21 References [1] PHP and MySQL Web Development (4th Edition). Luke Welling, Laura Thompson. Addison-Wesley Professional, 2014 [2] Fundamentals of Web Development. Randy Connolly, Ricardo Hoar. Pearson, 2014 php.net Lecture notes of Tufts University, Web Programming, 2011; Advanced Web Programming, 2007

WINTER. Web Development. Template. PHP Variables and Constants. Lecture

WINTER. Web Development. Template. PHP Variables and Constants. Lecture WINTER Template Web Development PHP Variables and Constants Lecture-3 Lecture Content What is Variable? Naming Convention & Scope PHP $ and $$ Variables PHP Constants Constant Definition Magic Constants