PHP $GLOBALS
Global Variables in PHP: Understanding and Implementation
Introduction:
Learn about global variables in PHP and how they allow you to access data from anywhere in your script. This lesson covers the basics of using global variables, provides examples, and discusses best practices. Gain insights into creating PHP applications with practical demonstrations.
In PHP, $GLOBALS is a superglobal variable that is used to access global variables from anywhere in a script, regardless of the scope.
It is an associative array where each key is the name of a global variable, and the corresponding value is the data stored in that variable.
Here’s a simple example:
<?php
$x = 10;
$y = 20;
function addGlobalVariables() {
// Accessing global variables using $GLOBALS
$GLOBALS['sum'] = $GLOBALS['x'] + $GLOBALS['y'];
}
addGlobalVariables();
// Accessing the global variable set in the function
echo $sum; // Outputs 30
?>- In this example, the function addGlobalVariables uses $GLOBALS to access the global variables $x and $y, performs the addition, and stores the result in a new global variable called $sum.
- Outside the function, we can then directly access $sum as it is now a global variable.
It’s important to note that using global variables extensively can make code harder to maintain and debug. It is generally considered good practice to minimize the use of global variables and prefer passing variables explicitly between functions or using other means of encapsulation.
How to Create Global Variables step by step?
- In PHP, global variables are those that can be accessed from anywhere in the script, both within functions and outside of them.
- You can create global variables using the $GLOBALS superglobal or by declaring the variable outside of any function or class.
Here’s a step-by-step guide:
Create Global Variables Using $GLOBALS Superglobal:
Define Global Variables:
Start by declaring your global variables outside of any function or class.
<?php $globalVariable1 = "Hello"; $globalVariable2 = 42; ?>
Access Global Variables Inside a Function:
Use the $GLOBALS superglobal to access the global variables within a function.
<?php
function myFunction() {
echo $GLOBALS['globalVariable1']; // Outputs: Hello
echo $GLOBALS['globalVariable2']; // Outputs: 42
}
myFunction();
?>Declaring Global Variables out side the function or class
Create Global Variables
You can also declare global variables outside functions or classes.
<?php $globalVariable1 = "Hello"; $globalVariable2 = 42; ?>
Access Global Variables Inside a Function:
Since the variables are declared outside functions, they are accessible globally.
<?php
function myFunction() {
global $globalVariable1, $globalVariable2;
echo $globalVariable1; // Outputs: Hello
echo $globalVariable2; // Outputs: 42
}
myFunction();
?>Remember, while global variables provide a convenient way to share data between different parts of your script, excessive use of global variables can make code harder to understand and maintain.
complete example in html with explanation
- Let’s create a simple HTML file with PHP to demonstrate global variables.
- In this example, we’ll have an HTML form where the can input two numbers.
- When the form is submitted, the PHP script will calculate the sum and display it.
index.php:
<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <meta name="viewport" content="width=device-width, initial-scale=1.0"> <title>Global Variables Example</title> </head> <body> <h2>Sum Calculator</h2> <!-- HTML form --> <form method="post" action="calculate.php"> <label for="num1">Number 1:</label> <input type="text" name="num1" required> <label for="num2">Number 2:</label> <input type="text" name="num2" required> <button type="submit">Calculate Sum</button> </form> </body> </html>
create :calculate.php:
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Calculation Result</title>
</head>
<body>
<h2>Calculation Result</h2>
<?php
// Check if form is submitted
if ($_SERVER["REQUEST_METHOD"] == "POST") {
// Accessing form data using $_POST
$num1 = $_POST["num1"];
$num2 = $_POST["num2"];
// Validate input (you may want to perform more robust validation)
if (!is_numeric($num1) || !is_numeric($num2)) {
echo "<p>Please enter valid numbers.</p>";
} else {
// Creating a global variable to store the sum
$GLOBALS['sum'] = $num1 + $num2;
// Displaying the result
echo "<p>Sum of $num1 and $num2 is: " . $GLOBALS['sum'] . "</p>";
}
} else {
// If form is not submitted, display a message
echo "<p>Please submit the form to calculate the sum.</p>";
}
?>
<p><a href="index.php">Go back to the form</a></p>
</body>
</html>Explanation:
index.php:
This is the main HTML file with a form that takes two numbers as input.
The form’s action attribute is set to “calculate.php,” which is the script that will handle the form submission.
calculate.php:
- This script receives the form data using $_POST.
- It checks if the form is submitted using $_SERVER[“REQUEST_METHOD”].
- Validates the input (ensures that the entered values are numeric).
- If validation passes, it calculates the sum and stores it in the global variable $GLOBALS[‘sum’].
- The result is displayed, and there is a link to go back to the form.
You can run this example by saving these files in the same directory and accessing index.php in a web browser. Enter two numbers in the form, submit it, and the calculated sum will be displayed on the result page.
Another example
- Let’s create another example where we have a global variable to keep track of the number of times a button is clicked.
- This example will consist of an HTML page with a button.
- Each time the button is clicked, it will trigger a PHP script to update and display the click count using a global variable.
Create :index.php:
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Click Counter</title>
</head>
<body>
<h2>Click Counter</h2>
<p>Click the button to increase the count:</p>
<!-- HTML button -->
<button onclick="updateCount()">Click me</button>
<!-- Display the click count using PHP -->
<p>Click count: <?php echo $GLOBALS['clickCount']; ?></p>
<!-- JavaScript function to trigger the PHP script -->
<script>
function updateCount() {
// Use AJAX to call the PHP script asynchronously
var xhr = new XMLHttpRequest();
xhr.open("GET", "updateCount.php", true);
xhr.send();
// Update the count displayed on the page (optional)
var currentCount = parseInt(document.getElementById("clickCount").innerText);
document.getElementById("clickCount").innerText = currentCount + 1;
}
</script>
</body>
</html>Create :updateCount.php:
<?php
// Initialize the click count if it doesn't exist
if (!isset($GLOBALS['clickCount'])) {
$GLOBALS['clickCount'] = 0;
}
// Increment the click count
$GLOBALS['clickCount']++;
// You can perform other operations here if needed
// Optionally, you can send a response (e.g., for AJAX requests)
echo "Click count updated to: " . $GLOBALS['clickCount'];
?>Explanation:
index.php:
- This HTML file includes a button that, when clicked, triggers a JavaScript function (updateCount) to make an asynchronous request to the updateCount.php script.
- It also displays the current click count using PHP (<?php echo $GLOBALS[‘clickCount’]; ?>).
updateCount.php:
- This PHP script initializes the click count if it doesn’t exist and increments it each time the script is called.
- It can perform additional operations if needed.
To run this example, save these files in the same directory, and open index.php in a web browser. Each time you click the button, the click count will increase, and the updated count will be displayed on the page without refreshing.
An application by this lesson with explanation
- Let’s create another simple PHP application that uses global variables to store information.
- This application will have a form to collect details, and upon submission, it will display the entered information on the page.
index.php:
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title> Information App</title>
</head>
<body>
<h2> Information App</h2>
<!-- HTML form -->
<form method="post" action="processForm.php">
<label for="name">name:</label>
<input type="text" name="name" required>
<label for="email">Email:</label>
<input type="email" name="email" required>
<button type="submit">Submit</button>
</form>
<!-- Display information using PHP -->
<?php
if (isset($GLOBALS['Info'])) {
echo "<h3>Entered Information:</h3>";
echo "<p>name: " . $GLOBALS['Info']['name'] . "</p>";
echo "<p>Email: " . $GLOBALS['Info']['email'] . "</p>";
}
?>
</body>
</html>
processForm.php:
<?php
// Initialize the information array if it doesn't exist
if (!isset($GLOBALS['Info'])) {
$GLOBALS['Info'] = [];
}
// Process the form data and store it in the global variable
if ($_SERVER["REQUEST_METHOD"] == "POST") {
$name = $_POST["name"];
$email = $_POST["email"];
// You can perform additional validation if needed
// Store the information in the global variable
$GLOBALS['Info'] = [
'name' => $name,
'email' => $email,
];
}
// Redirect back to the main page
header("Location: index.php");
exit;
?>Explanation:
index.php:
- This is the main page of our application with an HTML form to collect information.
- The form’s action attribute is set to “processForm.php,” which is the script that will handle form submission.
- The PHP code below the form checks if the global variable $Info is set and displays the entered information if available.
processForm.php:
- This script initializes the global variable $Info as an empty array if it doesn’t exist.
- It processes the form data submitted through the POST method, stores it in the global variable, and then redirects back to the main page (index.php).
To run this application:
- Save the above code for index.php and processForm.php into two separate files in the same directory.
- Open index.php in a web browser.
- Enter a name and email in the form and click “Submit.”
- The entered information will be displayed on the page.
This example demonstrates the use of global variables to store information across requests. However, keep in mind that in more complex applications, using global variables may not be the most optimal approach, and other methods like sessions or databases may be more suitable.
Quiz about PHP and global variables
Here’s a quiz about PHP and global variables.
Each question has multiple-choice answers, and the correct answer is indicated with the (Correct) tag.
1-What is a global variable in PHP?
a. A variable declared inside a function
b. A variable accessible from anywhere in the script (Correct)
c. A variable with a global scope
2-Which PHP superglobal is used to access global variables inside a function?
a. $GLOBALS (Correct)
b. $_POST
c. $_GET
3-When using global variables, what is a potential drawback?
a. Increased code readability
b. Code organization becomes more straightforward
c. Maintenance challenges and potential conflicts (Correct)
4-What is the purpose of the $GLOBALS superglobal?
a. To store session data
b. To access global variables from anywhere in the script (Correct)
c. To retrieve form data
5-In PHP, how can you declare a global variable outside of a function?
a. $globalVar;
b. global $globalVar; (Correct)
c. var $globalVar;
6-What is a good practice when working with global variables in PHP?
a. Use global variables extensively for simplicity
b. Minimize the use of global variables and prefer other means of encapsulation (Correct)
c. Always declare variables within functions
7-In the example, how is the sum calculated in the addGlobalVariables function?
a. Using a local variable
b. Using a session variable
c. Using the $GLOBALS superglobal (Correct)
8-What is the role of updateCount.php in the second example?
a. Displays the click count
b. Handles form submission
c. Updates the global variable and sends a response (Correct)
9-What is the purpose of the JavaScript function updateCount in the second example?
a. Validates form data
b. Sends an AJAX request to updateCount.php (Correct)
c. Displays the click count on the page
10-In the second example, what does the line:
document.getElementById(“clickCount”).innerText = xhr.responseText; do?
a. Retrieves the click count from the server
b. Updates the displayed click count on the page (Correct)
c. Clears the click count
11-What is the significance of header(“Location: index.php”); in processForm.php?
a. Displays an error message
b. Redirects back to the main page (Correct)
c. Ends the script execution
12-In the third example, what type of form input is used for the “Email” field?
a. text
b. email (Correct)
c. input
13-What does the line $GLOBALS[‘Info’] = [] do in processForm.php?
a. Declares a global variable
b. Initializes the global variable as an empty array (Correct)
c. Displays information
14-Why might using global variables in larger applications be less recommended?
a. Global variables improve code organization
b. Global variables may lead to maintenance challenges and potential conflicts (Correct)
c. Global variables speed up the execution of scripts
15-What is one alternative to using global variables for storing information across requests?
a. Cookies
b. Sessions (Correct)
c. Local variables