PHP Checkbox
Summary: in this tutorial, you will learn how to use PHP to process a form with one or more checkboxes.
A quick introduction to the checkbox element
A checkbox allows you to select a single value for submission in a form. To create a checkbox, you use the input element with the type checkbox as follows:
<input type="checkbox" name="checkbox_name" value="checkox_value">Code language: HTML, XML (xml)
A checkbox has two states: checked and unchecked.
If you check the checkbox and submit the form using the POST method, the $_POST associative array will contain an element whose key is checkbox_name and value is checkbox_value.
echo $_POST['checkbox_name']; // 'checkbox_value'Code language: PHP (php)
However, if you uncheck the checkbox and submit the form, the $_POST won’t have any element with key checkbox_name. It means that the following expression returns false:
isset($_POST['checkbox_name'])Code language: PHP (php)
To check if a checkbox is checked, you can also use the filter_has_var() function like this:
if(filter_has_var(INPUT_POST,'checkbox_name')) {
// ...
}Code language: JavaScript (javascript)
The filter_has_var() function returns true if the checkbox_name exists in the INPUT_POST.
A checkbox has no label. Therefore, you should always use a checkbox with a <label> element like this:
<input type="checkbox" name="agree" id="agree">
<label for="agree">I agree</label>Code language: HTML, XML (xml)
In this example, the value of the for attribute of the <label> element is the same as the value of the id attribute of the checkbox. When you associate a label with a checkbox, you can click the label to check or uncheck the checkbox.
Another way to associate a checkbox with a label is to place the checkbox inside the label like this:
<label>
<input type="checkbox" name="agree"> I agree
</label>Code language: HTML, XML (xml)
In this case, you don’t need to specify the id for the checkbox and the for attribute for the label.
A simple PHP checkbox example
We’ll create a simple form with one checkbox and a submit button.
First, create the following directory and file structure:
.
├── css
│ └── style.css
├── inc
│ ├── .htaccess
│ ├── get.php
│ └── post.php
└── index.phpCode language: plaintext (plaintext)
| File | Directory | Description |
|---|---|---|
| index.php | . | Contain the main logic that loads get.php or post.php depending on the HTTP request method |
| header.php | inc | Contain the header code |
| footer.php | inc | Contain the footer code |
| get.php | inc | Contain the code for showing a form with a checkbox when the HTTP request is GET. |
| post.php | inc | Contain the code for handling POST request |
| .htaccess | inc | Prevent direct access to the files in the inc directory |
| style.css | css | Contain the CSS code |
index.php
Second, add the following code to the index.php file:
require __DIR__ . '/inc/header.php';
$errors = [];
$request_method = $_SERVER['REQUEST_METHOD'];
if ($request_method === 'GET') {
require __DIR__ . '/inc/get.php';
} elseif ($request_method === 'POST') {
require __DIR__ . '/inc/post.php';
}
if ($errors) {
require __DIR__ . '/inc/get.php';
}
require __DIR__ . '/inc/footer.php';
Code language: PHP (php)
The index.php loads the form from the get.php file if the HTTP request method is GET. And it loads the post.php file if the form is submitted.
The $errors variable is used to store error messages.
header.php
Third, place the following code to the header.php file:
<html lang="en"><head>
<meta charset="UTF-8" />
<meta name="viewport" content="width=device-width, initial-scale=1.0" />
<title>PHP Checkbox</title>
<link rel="stylesheet" href="css/style.css">
</head>
<body class="center">
<main>
Code language: HTML, XML (xml)
footer.php
Fourth, the footer.php file contains the enclosing tags corresponding to the opening tags from the header.php file:
</main>
</body></html>
Code language: HTML, XML (xml)
get.php
Fifth, create a form in the get.php file:
<form action="<?php echo htmlspecialchars($_SERVER['PHP_SELF']) ?>" method="post">
<div>
<label for="agree"> <input type="checkbox" name="agree" value="yes" id="agree" /> I agree to the <a href="#" title="term of service"> Term of Service</a></label>
<small class="error"><?php echo $errors['agree'] ?? '' ?>
</small>
</div> <div>
<button type="submit">Join Us</button>
</div>
</form>
Code language: PHP (php)
post.php
Sixth, add the following code to the post.php file to sanitize and validate the form data:
// sanitize the value
$agree = filter_input(INPUT_POST, 'agree', FILTER_SANITIZE_STRING);
// check against the valid value
if ($agree) {
echo 'Thank you for joining us!';
} else {
$errors['agree'] = 'To join us, you need to agree to the TOS.';
}
Code language: PHP (php)
Summary
- Use the
isset()orfilter_has_var()to check if a checkbox is checked or not.