What are the best practices for handling form submissions and data validation in PHP to prevent common errors like undefined constants?

When handling form submissions in PHP, it is crucial to validate user input to prevent common errors like undefined constants. To avoid this issue, always check if the form fields are set before using them in your code. This can be done using the isset() function to ensure that the data is present before processing it. 

if(isset($_POST['submit'])) {
    $username = isset($_POST['username']) ? $_POST['username'] : '';
    $email = isset($_POST['email']) ? $_POST['email'] : '';
    
    // Validate and process the form data here
}

Keywords

form submissions data validation PHP undefined constants error prevention

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