How can PHP developers handle special characters like single quotes (') in user input to prevent errors or unexpected behavior?

Special characters like single quotes (') in user input can cause errors or unexpected behavior in PHP applications, especially if the input is directly used in SQL queries or output to the browser. To prevent this, PHP developers can use functions like addslashes() or mysqli_real_escape_string() to escape special characters before using the input in SQL queries. Another option is to use htmlspecialchars() to encode special characters before outputting the user input to the browser.

// Example of using mysqli_real_escape_string to handle single quotes in user input
$user_input = $_POST['user_input'];
$escaped_input = mysqli_real_escape_string($connection, $user_input);

// Example of using htmlspecialchars to handle special characters in user input before outputting to the browser
echo htmlspecialchars($user_input);