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

last week …• PHP origins & use• Basic Web 1.0 2-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 :r reading onlyw write only, create if necessary, discard previous contenta append to file, create if necessary, start writing at endr+ reading and writingw+ reading & writing, create if necessary, discard previous contenta+ 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($text){print("<b>$text</b>");

}

print("This Line is not Bold<br>\n");print_bold("This Line is Bold");print("<br>\n");print("This Line is not Bold<br>\n");

?>

User Defined Functions (2)

run code

• Calculator example (from last weeks workshop)<?phpfunction 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 = "<b>$text</b>";return($text);

}print("This Line is not Bold<br>\n");print(makeBold("This Line is Bold") . "<br>\n");print("This Line is not Bold<br>\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)

<?phpfor ($i = 0; $i < sizeof($array); $i++) {         print $array[$i]; }

?>

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 …