变量和变量作用域 | PHP 基础知识

Create Variable in PHP

The rules when you create variables in PHP:

1. Variable declaration with dollar ($) followed by variable name
2. Variable name must start with a letter or underscore (_)
3. Variable name is case-sensitive

Valid variables:

$name = "Gunawan"; //valid
$Name = "Gunawan"; //valid
$_name = "Gunawan; //valid

Not valid variables:

$4name = "Gunawan"; //not valid
$user-name = "Gunawan"; //not valid
$this = "Gunawan"; //not valid

Variable Scope

PHP has 3 variable scopes:

1. Global
2. Local
3. Static

Global scope

$name = "Gunawan";

function get_name() {
echo $name; // not valid
}

get_name();

To access a global variable within a function you must declare a global variable with the keyword 'global' within a function.

$name = "Gunawan";

function get_name() {
global $name;
echo $name; // valid
}

get_name();

Use Array GLOBALS to Access Global Variable

The second way to access global variables is to use a global array.

$name = "Gunawan";

function get_name() {
echo $GLOBALS['name']; // valid
}

get_name();

Static Variable

function test() {
static $number = 0;
echo $number;
$number++;
}

Variable Super Global in PHP:

1. $GLOBALS
2. $_SERVER
3. $_GET
4. $_POST
5. $_FILES
6. $_COOKIE
7. $_SESSION
8. $_REQUEST
9. $_ENV

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