Summary of PHP Global Variables

Introduction to PHP Global Variables

PHP global variables are built-in variables that are available in all scopes throughout a script. They provide a way to access data that is common to multiple parts of an application.

Key Concepts

• Global Scope: Variables declared outside of any function or class are in the global scope and can be accessed anywhere in the script.
• Superglobals: PHP provides several built-in superglobal arrays that are always accessible, regardless of scope. These include:
  • $_GET: Contains data sent to the script via URL parameters (query string).
  • $_POST: Contains data sent to the script via HTTP POST method.
  • $_COOKIE: Contains cookie data sent to the script.
  • $_SESSION: Used to store session variables.
  • $_FILES: Contains information about files uploaded through a form.
  • $_SERVER: Contains information about headers, paths, and script locations.
  • $_GLOBALS: A global associative array that holds all global variables.

Using Global Variables

To access a global variable inside a function, you need to use the global keyword:

Example

$globalVar = "I am a global variable";

function testGlobal() {
    global $globalVar; // Declare the variable as global
    echo $globalVar;   // Access the global variable
}

testGlobal(); // Outputs: I am a global variable

Conclusion

PHP global variables are essential for data sharing across different parts of a script. Understanding superglobals and the global keyword is crucial for effective PHP programming. These variables help maintain state and manage data flow in web applications.