PHP II¶

`print_r`¶

print_r is a function that recursively prints any object passed to it
- It is specifically designed to produce output that is readable by humans
- Very helpful for debugging
An optional second parameter can be set to true to force print_r to return a string rather than printing directly

In [ ]:

print_r(explode(',', "John,Paul,George,Ringo"));

In [ ]:

print_r(explode(',', "John,Paul,George,Ringo"),true);

Arrays¶

Arrays in PHP can either be
- associative
- indexed
Arrays are heterogeneous in PHP
Indexed using square brackets
- indexing starts at 0

Array Syntax¶

Arrays are created by calling the special array function
To initialize an indexed style array, pass the values separated by commas
```
$an_array = array(1,2,3,"Hello")
```
To intialize an associatve array, pass the key-value pairs separated by commas
- Key-value pairs are specified using the sytnax key => value

$assoc_array = array('course'=>'CMSC 433', 'title'=>'Scripting Languages');

In [ ]:

$assoc_array = array('course'=>'CMSC 433',
                     'title'=>'Scripting Languages',
                     'time'=> 11.5);
echo print_r($assoc_array,true);

Adding to an Array¶

To push a new element on the end of an array, assign the new element to the array indexed with empty square brackets
```
$an_array[] = 5;
```
To add a new element and a specific key, assign into the array indexed at that new key

$an_array['new_key'] = 10;

Either of these methods can be used with a previsouly undeclared variable to both create an array and insert one element into it

In [ ]:

$some_numbers = array(0,4,6,1,4,9,0,22);
$some_numbers[] = 100;
echo print_r($some_numbers,true)

In [ ]:

$ascii = array('A' => 65, 'B' => 66, 'a' => 97);
$ascii['b'] = 98;
echo print_r($ascii,true);

In [ ]:

$ascii = array('A' => 65, 'B' => 66, 'a' => 97);
$ascii[] = 98;
echo print_r($ascii,true);

Array Functions¶

For a full list of array functions, see the PHP manual
Some example functions:
- range
- count
- list
- array_slice
- array_chunk

Array Functions¶

For a full list of array functions, see the PHP manual
Some example functions:
- array_key_exists
- in_array
- shuffle
- array_sum
- sort

In [ ]:

echo print_r(range(1,10) ,true);

In [ ]:

## Range in PHP must take two parameters!
echo print_r(range(10),true);

In [ ]:

echo print_r(range(1,10,4),true);

In [ ]:

count(range(1,10));

In [ ]:

$info = array('coffee', 'brown', 'caffeine');
list($drink, $color, $power) = $info;
echo $drink;
echo $color;
echo $power;

In [ ]:

$my_range = range(1,10);
echo print_r(array_slice($my_range,3,7),true);

In [ ]:

echo print_r(array_slice($my_range,-4,6),true);

In [ ]:

echo print_r(array_chunk($my_range,2),true);

In [ ]:

array_key_exists('Dog',range(0,10));

In [ ]:

array_key_exists('Dog',array('Dog' => 40, 'Cat' => 20))

In [ ]:

in_array(10,range(0,10));

In [ ]:

in_array(10,range(0,5));

In [ ]:

in_array(10,array('ten' => 10, 'twenty' => 20));

In [ ]:

in_array(0,array('ten' => 10, 'twenty' => 20));

In [ ]:

shuffle(range(1,10));

In [ ]:

shuffle($my_range);
echo print_r($my_range,true);

In [ ]:

array_sum(array(1,2,3,"5",2.4));

Extract and Compact¶

extract and compact are two functions that allow you to convert from and to arrays respecitively
Rather than return anything, extract creates new variables with names based on the keys in the array
compact on the other hand takes a list of strings, and looks for variables with those names, creating an array out of them
- How would you write your own compact function?

In [ ]:

$info = array('school'=>'UMBC',
              'department'=>'CSEE',
              'building'=>'ITE');
extract($info);
echo print_r($info,true);
echo "The $department department of $school is located in $building";

In [ ]:

$name = 'Raúl González Blanco';
$position = "Forward";
$nationality = "Spanish";
$player = compact('name','position','nationality');
echo print_r($player,true);

Multi-Dimensional Arrays¶

Mutli-Dimensional arrays are fairly well supported in PHP
- You could make an array of arrays manually
Just like with a one-dimensional array, you can assign directly to mutliple indices with out ever declaring something as an array

In [ ]:

$matrix[0][] = 10;
$matrix[1][1] = 20;
$matrix[1]['Key'] = 30;
$matrix[1][] = 3;
$matrix[][][] = 40;
#shift($matrix,10);
echo print_r($matrix,true);

Loops¶

PHP has all the standard looping constructs
- While
- Do-While
- For
It also has a specific foreach construct
```
foreach($array as $element){
}
```

In [ ]:

$i = 10;
while($i > 0)
{
    echo $i;
    $i--;
}

In [ ]:

$i = 10;
do
{
    echo $i;
    $i--;
}while($i > 0); #Note the Semicolon

In [ ]:

for($i = 0; $i < 10; $i++){
echo $i;
}

In [ ]:

$to_loop = array('a', 'b', 'c', 'd', 'e');
foreach($to_loop as $el){
echo $el;
}

In [ ]:

$to_loop = array('a'=>97, 'b'=>98, 'c'=>99, 'd'=>100, 'e'=>101);
foreach($to_loop as $el){
echo $el;
}

In [ ]:

$to_loop = array('a'=>97, 'b'=>98, 'c'=>99, 'd'=>100, 'e'=>101);
foreach($to_loop as $k => $el){
echo $k, $el;
}

Function Definitions¶

Function in PHP are declared using the keyword function
- The parameters also use the $ notation
Function definitions can appear anywhere in a file
- Must be defined before they are used
Support returning by reference

In [ ]:

function my_first_function(){
    echo "Hello from inside a function";
}
my_first_function();
my_first_function();

In [ ]:

function someMath($number1, $number2){
    echo $number1 * $number2;
}
someMath(1,2);

In [ ]:

function someMath2($number1, $number2){
    return $number1 * $number2;
}
someMath2(1,2);

Scope Refresher¶

Remember in PHP scope is global, except in functions where it is local
- In functions, things in global scope aren't in scope either
We can modifiy the scope of a variable using two different keywords
- global
- static

In [ ]:

function scope_tester() {
        $a .= " World!";
        echo "a in scope_tester(): $a";
    }
$a = "Hello";
echo "a before scope_tester(): ", $a;
scope_tester();
echo "a after scope_tester(): ", $a;

In [ ]:

function scope_tester2() {
        $a .= " World!";
        echo "a in scope_tester(): $a";
    }
global $a;
$a = "Hello";
echo "a before scope_tester2(): ", $a;
scope_tester2();
echo "a after scope_tester2(): ", $a;

In [ ]:

function scope_tester3() {
        global $a;
        $a .= " World!";
        echo "a in scope_tester(): $a";
    }
$a = "Hello";
echo "a before scope_tester3(): ", $a;
scope_tester3();
echo "a after scope_tester3(): ", $a;

In [ ]:

function counter() {
        static $n = 0;
        $n++;
        return $n;
    }
echo counter();
echo counter();
echo counter();

Pass-by-Value and Pass-by-reference¶

By default PHP passes parameters by value
- Even arrays
- This is fine in most instances
If you want your function to modify a variable (like shuffle does), append an ampersand & before the variable in the definition
- Can't pass literals by reference

In [ ]:

function change_array($arr){
    $arr[0] = 20;
    echo $arr[0];
}
$my_array = range(0,10);
echo $my_array[0];
change_array($my_array);
echo $my_array[0];

In [ ]:

function change_array_correct(&$arr){
    $arr[0] = 20;
    echo $arr[0];
}
$my_array = range(0,10);
echo $my_array[0];
change_array_correct($my_array);
echo $my_array[0];

In [ ]:

change_array_correct(range(0,10));

Default Parameters¶

PHP allows default parameters, following the conventions of most languages that do so
- Optional parameters must appear after all non-optional parameters
- Parameters not pass will use their default value

In [ ]:

function say_hello($who = "World"){
    echo "Hello $who!";
}
say_hello();
say_hello("Class");

In [ ]:

function custom_range($end, $start = 0){
return range($start,$end);
}
echo print_r(custom_range(4),true);
echo print_r(custom_range(4,1),true);

Return¶

Just as with parameters, PHP allows values to be returned by either copy or reference
- By default, values that are returned are copied
To return by reference, place an amperstand (&) before the function name in the declaration
```
function &name(....)
{
}
```

In [ ]:

function getFredReturnByValue() {
    global $names;
    return $names[0];
}

function & getFredReturnByRef() {
    global $names;
    return $names[0];
}

$names = array("Fred", "Barney", "Wilma", "Betty");

In [ ]:

$fred = getFredReturnByValue();
echo $fred;
$fred = 'Bam Bam';
$fred = getFredReturnByValue();
echo $fred;

In [ ]:

$fred =& getFredReturnByRef();
echo $fred;
$fred = 'Bam Bam';
$fred =& getFredReturnByRef();
echo $fred;

Varags¶

To use a variable number of arguments in PHP, don't change the function signature at all
Inside the function, call the function func_get_args
- This returns an array holding the additional arguments

In [ ]:

function maximum() {
    $args = func_get_args();
    $max = $args[0];
    for($i = 1, $n = count($args); $i < $n; $i++) {
      $max = $args[$i] > $max ? $args[$i] : $max;
    }
    return $max;
  }
echo maximum(1,2,300,4,5,6);

Anonymous Functions¶

Since PHP 5.3, truly anoymous functions have been supported
To write one, provide the parameters directly after the function keyword
- This can be saved to a variable if you'd like, or passed directly to another function

In [ ]:

$max = function($a,$b){
    return ($a > $b)?$a:$b;
}; #Note the semicolon
$max(1,2);

Reading Files¶

PHP file reading can be done in a traditional manner using a file pointer
- fopen(file_name)
PHP also has numerous special functions meant to help with reading files
- file_get_contents(name)
- file(name)

In [ ]:

if($fp = fopen('hello.sh','r')){
    while($line = fgets($fp)){
        echo htmlspecialchars($line);
    }
}else{
    echo "Can't read file";
}

In [ ]:

htmlspecialchars(file_get_contents('hello.sh'));

In [ ]:

$contents = file('hello.sh');
echo print_r($contents,true);

Writing Files¶

Just as with reading files, PHP allows files to be written using
- The traditional file handle way
- A simplified function
  - file_put_contents (Since PHP 5 on)

In [ ]:

if($fp = fopen('hello.txt','w')){
    fwrite($fp, "Hello");
    fwrite($fp, " World\n");
    fwrite($fp, "You need to include new lines explicitly\n");
    fclose($fp); 
}else{
    echo "Can't open file";
}

In [ ]:

if($fp = fopen('hello.txt','a')){
    fwrite($fp, "Hello");
    fwrite($fp, " World\n");
    fwrite($fp, "You need to include new lines explicitly\n");
    fclose($fp); 
}else{
    echo "Can't open file";
}

In [ ]:

file_put_contents("hello.txt","This\nWrites\nIt\nAll at once!")

In [ ]:

file_put_contents("hello.txt","This\nWrites\nIt\nAll at once!",FILE_APPEND)

In [ ]:

file_put_contents("range.txt",range(0,20));

Locking Files¶

In general, you should expect your PHP script to be running multiple copies of itself at once
- Lots of people are going to be on your website constantly
When you lock a file in PHP, it only prevents other PHP processes from accessing it

In [ ]:

if($fp = fopen('hello.txt','a')){
    if(flock($fp,LOCK_EX)){
    fwrite($fp, "Hello");
    fwrite($fp, " World\n");
    fwrite($fp, "You need to include new lines explicitly\n");
    flock($fp,LOCK_UN);
    fclose($fp); }
    else{
     echo "Couldn't get lock";
    }
}else{
    echo "Can't open file";
}

In [ ]:

file_put_contents("range.txt",range(0,20),LOCK_EX);

Externalizing Code¶

To pull in code from another location, there are several functions PHP provides
- include(file_name) - Includes and evaluates the file
- require(file_name) - Includes and evaluates the file, killing the script if unable to do so
- include_once(file_name) - Only include and evaluate this file one time
- require_once(file_name) - Only require this file one time

In [ ]:

include 'header.php'; #same as include('header.php')

In [ ]:

include 'I dont exist';

In [ ]:

require 'I dont exist';

In [ ]:

include_once 'header.php';
include_once 'header.php';

PHP II¶

print_r¶

Arrays¶

Array Syntax¶

Adding to an Array¶

Array Functions¶

Array Functions¶

Extract and Compact¶

Multi-Dimensional Arrays¶

Loops¶

Function Definitions¶

Scope Refresher¶

Pass-by-Value and Pass-by-reference¶

Default Parameters¶

Return¶

Varags¶

Anonymous Functions¶

Reading Files¶

Writing Files¶

Locking Files¶

Externalizing Code¶

`print_r`¶