Intermediate PHP (2) File Input/Output & User Defined Functions

last week … PHP origins & use Basic Web tier/3-tier architecture with PHP PHP as a scripting language (supporting procedural & oo paradigms) Basic structure & use (statements, variables, control structures, operators) PHP data types - 5 basic – integer, floating-point, string, boolean & NULL & 3 complex - array, hash & object PHP Functions Library (700+) – string handling, input/output, date & time, db interaction, xml processing etc. etc. the exit & die() statements

File Input / Output & Disk Access (1) Reading and Writing to Files Communicating with files follows the pattern of opening a stream to a file, reading from or writing to it, and then closing the stream. fopen(..) : the fopen function opens a file for reading or writing. The function expects the name of a file and a mode e.g. fopen (‘c:/temp/myfile.txt’, ‘r’); which opens a file called ‘myfile.txt’ in the directory ‘c:/temp’ in the “read” mode File read/write modes : rreading only wwrite only, create if necessary, discard previous content aappend to file, create if necessary, start writing at end r+reading and writing w+reading & writing, create if necessary, discard previous content a+reading & writing, create if necessary, start writing at end

Input / Output & Disk Access (2) fclose (resource file) : used to close a file. feof (resource file) : as a file is read, php keeps a pointer to the last place in the file read; the feof function returns true if the end of file is reached. fgetcsv(resource file, integer length, string separator) : used for reading comma-separated data from a file. The optional separator argument specifies the character to separate fileds. If left out, a comma is used. fgets(resource file, integer length) : returns a string that reads from a file. It will attempt to read as many characters – 1 as specified by the length value. A line-break character is treated as a stopping point, as is the end of the file. fwrite(resource file, string data, integer length) : writes a string to a file. The length argument is optional and sets the number of bytes to write.

User Defined Functions (1) Functions are re-usable blocks of code that can referenced over and over again. Arguments can be passed to functions and values can be returned by them. -arguments & return values can be passed by value or reference -PHP can create functions dynamically at run-time (Lambda –Style) -References to functions can be held in variables (or arrays) - allowing functions to be a passed as arguments to other functions - Declaring a function - functions are declared using the function statement, a name and parenthesis () e.g. function my_function() {…..} - functions can accept any number of arguments and these are separated by commas inside the parenthesis e.g. function my_function($arg1, $arg2) {…..}

the following simple function prints out any text passed to it as bold <?php function print_bold($text){ print(" $text "); } print("This Line is not Bold \n"); print_bold("This Line is Bold"); print(" \n"); print("This Line is not Bold \n"); ?> User Defined Functions (2) run code

Calculator example (from last weeks workshop) <?php function calculate($x, $y, $op) { switch($op) { case '+': $prod = $x + $y; break; case '-': $prod = $x - $y; break; case '*': $prod = $x * $y; break; case '/': $prod = $x / $y; break; } return $prod; } $x = 33; $y = 77; $op = '*'; $prod = calculate($x, $y, $op); echo "$x $op $y = $prod"; ?> User Defined Functions (3) run code

- the return statement - at some point the function will finish and is ready to return control to the caller - execution then picks up directly after the point the function was called - it is possible to have multiple return points from a function (but this will reduce code readability) - if a return statement includes an expression, return(expression), the value of the expression will be passed back - see calculator example on previous page & below <?php function makeBold($text){ $text = " $text "; return($text); } print("This Line is not Bold \n"); print(makeBold("This Line is Bold"). " \n"); print("This Line is not Bold \n"); ?> User Defined Functions (4)

- values and references - for most data types, return values are passed by value - for objects, discussed next week, return values are returned by reference - the following function creates a new array of 10 random numbers between 1 and 100 and passes it back as a reference <?php function &get_rand_array() { $a = array(); for($i=0; $i<10; $i++) { $a[] = rand(1,100); } return($a); } $my_new_array = &get_rand_array(); print_r($my_new_array); ?> User Defined Functions (5) run code

User Defined Functions (6) - scope - scoping is way of avoiding name clashes between variables in different functions - each code block belongs to a certain scope - variables within functions have local scope and are private to the function - variables outside a function have a global scope <?php $a = 1; // global scope function test(){ echo $a; // reference to local scope variable } test(); ?> The above example will output nothing because the $a inside the function has local scope

- the global keyword can be used to access variables from the global scope within functions <?php $a = 1; $b = 2; function sum(){ global $a, $b; $b = $a + $b; } sum(); echo $b; ?> - The above script will output 3. By declaring $a and $b global within the function, all references to either variable will refer to the global version. There is no limit to the number of global variables that can be manipulated by a function. (Is it a good idea to use globals in this way?) User Defined Functions (7)

- arguments - functions expect arguments to be preceded by a dollar sign ($) and these are usually passed to the function as values - if an argument has a & sign in front - it is treated as a reference - the following example shows an argument passed as reference <?php function strip_commas(&$text){ $text = str_replace(",", "", $text); } $my_number = "10,000"; stripCommas($my_number); print($my_number); ?> User Defined Functions (8)

-default values - a function can use a default value in an argument using the = sign to precede the argument - consider the following example <?php function setName($FirstName = "John", $LastName = "Smith"){ return "Hello, $FirstName $LastName!\n"; } ?> - So, to greet someone called John Smith, you would just use: setName(); - To greet someone called Tom Davies, you would use: setName("Tom", "Davies"); - To greet someone called Tom Smith, you would use: setName("Tom"); User Defined Functions (9)

recursive functions (1) - recursive functions are functions that call themselves (self-calling) or to be sung to the tune of "When the Moon Hits Your Eye": "When a function calls a function in a Turing machine... that's recu-u-u-u-ursion!" or to put it simply: recursion means anything that references itself. -compare with iteration -example of iteration (print out all the values of an array) <?php for ($i = 0; $i < sizeof($array); $i++) { print $array[$i]; }sizeof ?> User Defined Functions (10)

recursive functions (2) - Mathematically speaking, a factorial (denoted by "!") is the result of a number multiplied by all positive integers less than that number. Non- integer and negative values are considered undefined. Zero factorial (0!), however, is defined as 1. e.g. 6! = 6 * 5 * 4 * 3 * 2 * 1 or 720 <?php function factorial($number) { if ($number < 2) { return 1; } else { return ($number * factorial($number-1)); } } print factorial(6); ?> User Defined Functions (11) run code

anonymous functions (run-time or dynamically created functions) - it is possible for PHP to use the value of an input (e.g. from a form) and change the definition of a function based on the input - example using calculator (last week’s workshop) <?php $add = create_function('$a,$b', 'return $a + $b;'); $subtract = create_function('$a,$b', 'return $a - $b;'); $multiply = create_function('$a,$b', 'return $a * $b;'); $divide = create_function('$a,$b', 'return $a / $b;'); extract($_GET); $fn = ${$op}; echo "$x $op $y = ". $fn($x,$y); ?> - Note the above example also illustrates how you can store a function name in a variable. User Defined Functions (12)

DB connectivity and processing forms processing sessions & cookies next week …