Php Reserved Words

Front 1

and

Back 1

a logical operator,
This key word is use with if statements. The code block will only be executed when TWO or more conditions links by this logical and keyword are BOTH true. These two symbols && are identical to the keyword and.

Hint 1

$a = 3;
$b = 7;

if (a== 3 and b == 7) {

// these statements executed
// only when BOTH a=3 and
// b = 7

}

Front 2

array

Back 2

Declares an array type.

An array type stores an organized list of information, sometimes, key/ value pairs.

Hint 2

<?php
$fruits = array (
"fruits" => array("a" => "orange", "b" => "banana", "c" => "apple"),
"numbers" => array(1, 2, 3, 4, 5, 6),
"holes" => array("first", 5 => "second", "third")
);
?>

Front 3

as

Back 3

use with

foreach ( as )

The foreach construct provides an easy way to iterate over arrays. foreach works only on arrays and objects, and will issue an error when you try to use it on a variable with a different data type or an uninitialized variable.

Front 4

break

Back 4

break ends execution of the current for, foreach, while, do-while or switch structure.

Hint 4

<?php
$arr = array('one', 'two', 'three', 'four', 'stop', 'five');
while (list(, $val) = each($arr)) {
if ($val == 'stop') {
break; /* You could also write 'break 1;' here. */
}
echo "$val<br />\n";
}

/* Using the optional argument. */

$i = 0;
while (++$i) {
switch ($i) {
case 5:
echo "At 5<br />\n";
break 1; /* Exit only the switch. */
case 10:
echo "At 10; quitting<br />\n";
break 2; /* Exit the switch and the while. */
default:
break;
}
}
?>

Front 5

callable

Back 5

Callbacks can be denoted by callable type hint as of PHP 5.4. This documentation used callback type information for the same purpose.

Some functions like call_user_func() or usort() accept user-defined callback functions as a parameter. Callback functions can not only be simple functions, but also object methods, including static class methods.

Passing

A PHP function is passed by its name as a string. Any built-in or user-defined function can be used, except language constructs such as: array(), echo, empty(), eval(), exit(), isset(), list(), print or unset().

Hint 5

<?php

// An example callback function
function my_callback_function() {
echo 'hello world!';
}

// An example callback method
class MyClass {
static function myCallbackMethod() {
echo 'Hello World!';
}
}

// Type 1: Simple callback
call_user_func('my_callback_function');

// Type 2: Static class method call
call_user_func(array('MyClass', 'myCallbackMethod'));

// Type 3: Object method call
$obj = new MyClass();
call_user_func(array($obj, 'myCallbackMethod'));

// Type 4: Static class method call (As of PHP 5.2.3)
call_user_func('MyClass::myCallbackMethod');

// Type 5: Relative static class method call (As of PHP 5.3.0)
class A {
public static function who() {
echo "A\n";
}
}

class B extends A {
public static function who() {
echo "B\n";
}
}

call_user_func(array('B', 'parent::who')); // A
?>

Front 6

case

Back 6

Always used with a switch statement to designate one condition of a variable that that will lead to code block being executed.

The switch statement is similar to a series of IF statements on the same expression. In many occasions, you may want to compare the same variable (or expression) with many different values, and execute a different piece of code depending on which value it equals to. This is exactly what the switch statement is for.

Hint 6

<?php
if ($i == 0) {
echo "i equals 0";
} elseif ($i == 1) {
echo "i equals 1";
} elseif ($i == 2) {
echo "i equals 2";
}

switch ($i) {
case 0:
echo "i equals 0";
break;
case 1:
echo "i equals 1";
break;
case 2:
echo "i equals 2";
break;
}
?>

Front 7

catch

Back 7

PHP 5 has an exception model similar to that of other programming languages. An exception can be thrown, and caught ("catched") within PHP. Code may be surrounded in a try block, to facilitate the catching of potential exceptions. Each try must have at least one corresponding catch block. Multiple catch blocks can be used to catch different classes of exceptions. Normal execution (when no exception is thrown within the try block, or when a catch matching the thrown exception's class is not present) will continue after that last catch block defined in sequence. Exceptions can be thrown (or re-thrown) within a catch block.

When an exception is thrown, code following the statement will not be executed, and PHP will attempt to find the first matching catch block. If an exception is not caught, a PHP Fatal Error will be issued with an "Uncaught Exception ..." message, unless a handler has been defined with set_exception_handler().

The thrown object must be an instance of the Exception class or a subclass of Exception. Trying to throw an object that is not will result in a PHP Fatal Error.

Hint 7

<?php
function inverse($x) {
if (!$x) {
throw new Exception('Division by zero.');
}
else return 1/$x;
}

try {
echo inverse(5) . "\n";
echo inverse(0) . "\n";
} catch (Exception $e) {
echo 'Caught exception: ', $e->getMessage(), "\n";
}

// Continue execution
echo 'Hello World';
?>

Front 8

class

Back 8

A class is a collection of variables and functions working with these variables. Variables are defined by var and functions by function. A class is defined using the following syntax:

Hint 8

<?php
class Cart {
var $items; // Items in our shopping cart

// Add $num articles of $artnr to the cart

function add_item($artnr, $num) {
$this->items[$artnr] += $num;
}

// Take $num articles of $artnr out of the cart

function remove_item($artnr, $num) {
if ($this->items[$artnr] > $num) {
$this->items[$artnr] -= $num;
return true;
} elseif ($this->items[$artnr] == $num) {
unset($this->items[$artnr]);
return true;
} else {
return false;
}
}
}
?>

Front 9

clone

Back 9

Creating a copy of an object with fully replicated properties is not always the wanted behavior. A good example of the need for copy constructors, is if you have an object which represents a GTK window and the object holds the resource of this GTK window, when you create a duplicate you might want to create a new window with the same properties and have the new object hold the resource of the new window. Another example is if your object holds a reference to another object which it uses and when you replicate the parent object you want to create a new instance of this other object so that the replica has its own separate copy.

An object copy is created by using the clone keyword (which calls the object's __clone() method if possible). An object's __clone() method cannot be called directly.

Hint 9

<?php
class SubObject
{
static $instances = 0;
public $instance;

public function __construct() {
$this->instance = ++self::$instances;
}

public function __clone() {
$this->instance = ++self::$instances;
}
}

class MyCloneable
{
public $object1;
public $object2;

function __clone()
{
// Force a copy of this->object, otherwise
// it will point to same object.
$this->object1 = clone $this->object1;
}
}

$obj = new MyCloneable();

$obj->object1 = new SubObject();
$obj->object2 = new SubObject();

$obj2 = clone $obj;


print("Original Object:\n");
print_r($obj);

print("Cloned Object:\n");
print_r($obj2);

?>

Front 10

const

Back 10

Class Constants

It is possible to define constant values on a per-class basis remaining the same and unchangeable. Constants differ from normal variables in that you don't use the $ symbol to declare or use them.

The value must be a constant expression, not (for example) a variable, a property, a result of a mathematical operation, or a function call.

It's also possible for interfaces to have constants. Look at the interface documentation for examples.

As of PHP 5.3.0, it's possible to reference the class using a variable. The variable's value can not be a keyword (e.g. self, parent and static).

Hint 10

<?php
class MyClass
{
const constant = 'constant value';

function showConstant() {
echo self::constant . "\n";
}
}

echo MyClass::constant . "\n";

$classname = "MyClass";
echo $classname::constant . "\n"; // As of PHP 5.3.0

$class = new MyClass();
$class->showConstant();

echo $class::constant."\n"; // As of PHP 5.3.0
?>

Front 11

continue

Back 11

continue

(PHP 4, PHP 5)

continue is used within looping structures to skip the rest of the current loop iteration and continue execution at the condition evaluation and then the beginning of the next iteration.

Hint 11

<?php
while (list($key, $value) = each($arr)) {
if (!($key % 2)) { // skip odd members
continue;
}
do_something_odd($value);
}

$i = 0;
while ($i++ < 5) {
echo "Outer<br />\n";
while (1) {
echo "Middle<br />\n";
while (1) {
echo "Inner<br />\n";
continue 3;
}
echo "This never gets output.<br />\n";
}
echo "Neither does this.<br />\n";
}
?>

Front 12

declare

Back 12

(PHP 4, PHP 5)

The declare construct is used to set execution directives for a block of code. The syntax of declare is similar to the syntax of other flow control constructs:

declare (directive)
statement
The directive section allows the behavior of the declare block to be set. Currently only two directives are recognized: the ticks directive (See below for more information on the ticks directive) and the encoding directive (See below for more information on the encoding directive).

Note: The encoding directive was added in PHP 5.3.0

The statement part of the declare block will be executed - how it is executed and what side effects occur during execution may depend on the directive set in the directive block.

The declare construct can also be used in the global scope, affecting all code following it (however if the file with declare was included then it does not affect the parent file).

Hint 12

<?php
// these are the same:

// you can use this:
declare(ticks=1) {
// entire script here
}

// or you can use this:
declare(ticks=1);
// entire script here
?>

Front 13

default

Back 13

This is used with a switch statement as a catch all option.

A special case is the default case. This case matches anything that wasn't matched by the other cases.

Hint 13

<?php
switch ($i) {
case 0:
echo "i equals 0";
break;
case 1:
echo "i equals 1";
break;
case 2:
echo "i equals 2";
break;
default:
echo "i is not equal to 0, 1 or 2";
}
?>

Front 14

die()

Back 14

(PHP 4, PHP 5)

die — Equivalent to exit

Hint 14

<?php
function error_msg($text) {
# add other stuff you may want here
$hello_var = 'hello'; //example of addon to beginning
$goodbye_var = 'goodbye'; //example of addon to end
die($hello_var.'<br />'.$text.'<br />'.$goodbye_var);
}

error_msg('how are you?');
?>

Outputs:
hello
how are you?
goodbye

Front 15

do

Back 15

part of do-while

do-while loops are very similar to while loops, except the truth expression is checked at the end of each iteration instead of in the beginning. The main difference from regular while loops is that the first iteration of a do-while loop is guaranteed to run (the truth expression is only checked at the end of the iteration), whereas it may not necessarily run with a regular while loop (the truth expression is checked at the beginning of each iteration, if it evaluates to FALSE right from the beginning, the loop execution would end immediately).

Hint 15

<?php
$i = 0;
do {
echo $i;
} while ($i > 0);
?>

Front 16

echo

Back 16

(PHP 4, PHP 5)

echo — Output one or more strings

Report a bug
Description

void echo ( string $arg1 [, string $... ] )
Outputs all parameters.

echo is not actually a function (it is a language construct), so you are not required to use parentheses with it. echo (unlike some other language constructs) does not behave like a function, so it cannot always be used in the context of a function. Additionally, if you want to pass more than one parameter to echo, the parameters must not be enclosed within parentheses.

echo also has a shortcut syntax, where you can immediately follow the opening tag with an equals sign. This short syntax only works with the short_open_tag configuration setting enabled.

Hint 16

<?php
echo "Hello World";

echo "This spans
multiple lines. The newlines will be
output as well";

echo "This spans\nmultiple lines. The newlines will be\noutput as well.";

echo "Escaping characters is done \"Like this\".";

// You can use variables inside of an echo statement
$foo = "foobar";
$bar = "barbaz";

echo "foo is $foo"; // foo is foobar

Front 17

else

Back 17

(PHP 4, PHP 5)

Often you'd want to execute a statement if a certain condition is met, and a different statement if the condition is not met. This is what else is for. else extends an if statement to execute a statement in case the expression in the if statement evaluates to FALSE. For example, the following code would display a is greater than b if $a is greater than $b, and a is NOT greater than b otherwise:

Hint 17

<?php
if ($a > $b) {
echo "a is greater than b";
} else {
echo "a is NOT greater than b";
}
?>

Front 18

elseif

Back 18

(PHP 4, PHP 5)

elseif, as its name suggests, is a combination of if and else. Like else, it extends an if statement to execute a different statement in case the original if expression evaluates to FALSE. However, unlike else, it will execute that alternative expression only if the elseif conditional expression evaluates to TRUE. For example, the following code would display a is bigger than b, a equal to b or a is smaller than b:

Hint 18

(PHP 4, PHP 5)

elseif, as its name suggests, is a combination of if and else. Like else, it extends an if statement to execute a different statement in case the original if expression evaluates to FALSE. However, unlike else, it will execute that alternative expression only if the elseif conditional expression evaluates to TRUE. For example, the following code would display a is bigger than b, a equal to b or a is smaller than b:

Front 19

empty()

Back 19

(PHP 4, PHP 5)

empty — Determine whether a variable is empty

Report a bug
Description

bool empty ( mixed $var )
Determine whether a variable is considered to be empty. A variable is considered empty if it does not exist or if its value equals FALSE. empty() does not generate a warning if the variable does not exist.

Hint 19

<?php
$var = 0;

// Evaluates to true because $var is empty
if (empty($var)) {
echo '$var is either 0, empty, or not set at all';
}

// Evaluates as true because $var is set
if (isset($var)) {
echo '$var is set even though it is empty';
}
?>

Front 20

enddeclare

Back 20

declare

(PHP 4, PHP 5)

The declare construct is used to set execution directives for a block of code. The syntax of declare is similar to the syntax of other flow control constructs:

declare (directive)
statement
The directive section allows the behavior of the declare block to be set. Currently only two directives are recognized: the ticks directive (See below for more information on the ticks directive) and the encoding directive (See below for more information on the encoding directive).

Note: The encoding directive was added in PHP 5.3.0

The statement part of the declare block will be executed - how it is executed and what side effects occur during execution may depend on the directive set in the directive block.

The declare construct can also be used in the global scope, affecting all code following it (however if the file with declare was included then it does not affect the parent file).

Front 21

endfor

Back 21

(PHP 4, PHP 5)

PHP offers an alternative syntax for some of its control structures; namely, if, while, for, foreach, and switch. In each case, the basic form of the alternate syntax is to change the opening brace to a colon (:) and the closing brace to endif;, endwhile;, endfor;, endforeach;, or endswitch;, respectively.

Front 22

endif

Back 22

(PHP 4, PHP 5)

PHP offers an alternative syntax for some of its control structures; namely, if, while, for, foreach, and switch. In each case, the basic form of the alternate syntax is to change the opening brace to a colon (:) and the closing brace to endif;, endwhile;, endfor;, endforeach;, or endswitch;, respectively.

<?php if ($a == 5): ?>
A is equal to 5
<?php endif; ?>
In the above example, the HTML block "A is equal to 5" is nested within an if statement written in the alternative syntax. The HTML block would be displayed only if $a is equal to 5.

The alternative syntax applies to else and elseif as well. The following is an if structure with elseif and else in the alternative format.

Front 23

eval

Back 23

(PHP 4, PHP 5)

eval — Evaluate a string as PHP code

Hint 23

<?php
$string = 'cup';
$name = 'coffee';
$str = 'This is a $string with my $name in it.';
echo $str. "\n";
eval("\$str = \"$str\";");
echo $str. "\n";
?>
The above example will output:
This is a $string with my $name in it.
This is a cup with my coffee in it.

Front 24

exit()

Back 24

Terminates execution of the script. Shutdown functions and object destructors will always be executed even if exit is called.

exit is a language construct and it can be called without parentheses if no status is passed.

Hint 24

<?php

//exit program normally
exit;
exit();
exit(0);

//exit with an error code
exit(1);
exit(0376); //octal

?>

Front 25

extends

Back 25

used with the keyword class to make it a sub-class of another class. The class that uses the extends keyword is known as the child class or sub-class. The class the was extended is called the parent class or super class.

class

A class is a collection of variables and functions working with these variables. Variables are defined by var and functions by function. A class is defined using the following syntax:

Hint 25

class Foo {
static function bar() { echo 'yep, this is Foo::bar'; }
}

class Bar extends Foo { }

Front 26

final

Back 26

Final Keyword

PHP 5 introduces the final keyword, which prevents child classes from overriding a method by prefixing the definition with final. If the class itself is being defined final then it cannot be extended.

Hint 26

<?php
class BaseClass {
public function test() {
echo "BaseClass::test() called\n";
}

final public function moreTesting() {
echo "BaseClass::moreTesting() called\n";
}
}

class ChildClass extends BaseClass {
public function moreTesting() {
echo "ChildClass::moreTesting() called\n";
}
}
// Results in Fatal error: Cannot override final method BaseClass::moreTesting()
?>