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UFCE8V-20-3 Information Systems Development 3 (SHAPE HK) Lecture 3 PHP (2) : Functions, User Defined Functions & Environment Variables.

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Presentation on theme: "UFCE8V-20-3 Information Systems Development 3 (SHAPE HK) Lecture 3 PHP (2) : Functions, User Defined Functions & Environment Variables."— Presentation transcript:

1 UFCE8V-20-3 Information Systems Development 3 (SHAPE HK) Lecture 3 PHP (2) : Functions, User Defined Functions & Environment Variables

2 last lecture … o PHP origins & use o Basic Web tier/3-tier architecture with PHP o PHP as a scripting language (supporting procedural & oo paradigms) o Basic structure & use (statements, variables, control structures, operators) o PHP data types - 5 basic – integer, floating-point, string, boolean & NULL & 3 complex - array, hash & object o the exit() & die() statements

3 PHP Functions (1) : inbuilt function library (700+) o Basic tasks –String Handling –Mathematics – random numbers, trig functions.. –Regular Expressions –Date and time handling –File Input and Output o And more specific functions for - –Database interaction – - MySQL, Oracle, Postgres, Sybase, MSSQL.. –Encryption –Text translation –Spell-checking –Image creation –XML etc.etc.

4 PHP Functions (2) : some commonly used built-in functions FunctionPurposeExample echo() prints text echo "Hello World"; explode() returns a string as an array split on the specified delimiter $pizza = "piece1 piece2 piece3"; $pieces = explode(" ", $pizza); echo $pieces[1]; // piece2 implode() opposite of explode – joins all the elements of an array using the specified delimiter $array = array('lastname', ' ', 'phone'); $comma_separated = implode(",", $array); //prints lastname, ,phone echo $comma_separated; isset() returns TRUE if a variable exists or FALSE if not isset($a); fopen() opens a file for reading (“r” ) or (“w”) writing. Use in conjunction with fclose. $filename = " myfile.txt " ; $handle = fopen($filename, " r " ); $contents = fread($handle, filesize($filename)); fclose($ini_handle);

5 PHP Functions (3) : user defined functions o Declaring a function - functions are declared using the function statement, a name and parenthesis () e.g function myfunction() {…..} - functions can accept any number of arguments and these are separated by commas inside the parenthesis e.g function myFunction(arg1, arg2) {…..} - the following simple function prints out any text passed to it as bold run example

6 o 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 - example: PHP Functions (4) : user defined functions run example

7 - values and references - for most data types, return values are passed by value - for objects, 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 Functions (5) : user defined functions run example

8 - scope (1) - scoping is way of avoiding 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 The above example will output nothing because the $a inside the function has local scope PHP Functions (6) : user defined functions

9 - the global keyword can be used to access variables from the global scope within functions - 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. PHP Functions (7) : user defined functions run example

10 - arguments - functions expect arguments to 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 Functions (8) : user defined functions run example

11 -default values - a function can use a default value in an argument using the = sign to precede the argument - consider the following example - So, to greet someone called John Smith, you could just use this: setName(); - To greet someone called Tom Davies, you would use this: setName("Tom", "Davies"); - To greet someone called Tom Smith, you would use this: setName("Tom"); PHP Functions (9) : user defined functions

12 Environment & other predefined variables (1) o PHP provides a large number of predefined variables to all scripts. o These variables represent everything from external variables to built-in environment variables, last error messages to last retrieved headers.external variables $GLOBALS $GLOBALS — References all variables available in global scope $_SERVER$_SERVER — Server and execution environment information $_GET$_GET — HTTP GET variables $_POST$_POST — HTTP POST variables $_FILES$_FILES — HTTP File Upload variables $_REQUEST$_REQUEST — HTTP Request variables $_SESSION$_SESSION — Session variables $_ENV$_ENV — Environment variables $_COOKIE$_COOKIE — HTTP Cookies $php_errormsg$php_errormsg — The previous error message $HTTP_RAW_POST_DATA$HTTP_RAW_POST_DATA — Raw POST data $http_response_header$http_response_header — HTTP response headers $argc$argc — The number of arguments passed to script $argv$argv — Array of arguments passed to script

13 o Some predefined variables are available to every script in every scope (both local and global) and these are referred to as Superglobals.Superglobals o For these, there is no need to do global $variable ; to access them within functions or methods. o The superglobals are: Environment & other predefined variables (2) $GLOBALS $_SERVER $_GET $_POST $_FILES $_COOKIE $_SESSION $_REQUEST $_ENV

14 Environment & other predefined variables (3): the $_REQUEST, $_GET & $_POST globals o The most commonly used global variables are $_GET and $_POST which are used to send data from the browser to the server. o $_GET is an associative array (hash) that passes values to the current script using URL parameters. - although the HTTP protocol does not set a limit to how long URL’s can be – different browsers do – so it is considered good practice not to send data that is more than 2000 characters with $_GET - because the values of $_GET can be read in the URL – no data containing sensitive information (like passwords) should be sent using $_GET - $_GET can't be used to send binary data, like images or word documents, just textual data.

15 Environment & other predefined variables (4): $_GET example " method="GET"> Name: Age: checks if either the ‘name’ or ‘age’ params. have values set html form with 3 inputs form method set to ‘GET’ $PHP_SELF returns path and name of current script ** Notice that once the form fields are filled in with values of say ‘Popeye’ and ‘83’, the URL shows as i.e. the parameters are now part of the URL. view script run script

16 o The POST method transfers information via HTTP headers. - the POST method does not have any restriction on data size to be sent. - it can be used to send ASCII as well as binary data. - the data sent by POST method goes through HTTP header so security depends on HTTP protocol. By using Secure HTTP (HTTPS) the data can be secured (to a certain extent). - PHP provides the $_POST associative array to access all the sent data using the POST method. ** Note that the example used in the previous slide can be easily changed to make use of the POST method by simply changing the method="GET" to method="POST". The parameters no longer appear in the URL. o $_REQUEST is an associative array (hash) that by default contains all of the contents of $_GET, $_POST and $_COOKIE together. ($_COOKIE superglobal will be discussed when we consider PHP sessions).array$_GET$_POST$_COOKIE Environment & other predefined variables (5): $_POST & $_REQUEST view scriptview script run scriptrun script

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