In PHP, what are some common functions used to validate and filter user input before processing it further?

When dealing with user input in PHP, it is essential to validate and filter the data to prevent security vulnerabilities such as SQL injection or cross-site scripting attacks. Some common functions used for this purpose are filter_var(), htmlspecialchars(), and mysqli_real_escape_string(). These functions help sanitize and validate user input before processing it further. 

// Example of using filter_var() to validate user input
$user_input = $_POST['user_input'];
$filtered_input = filter_var($user_input, FILTER_SANITIZE_STRING);
```

```php
// Example of using htmlspecialchars() to filter user input
$user_input = $_POST['user_input'];
$filtered_input = htmlspecialchars($user_input, ENT_QUOTES, 'UTF-8');
```

```php
// Example of using mysqli_real_escape_string() to validate user input
$user_input = $_POST['user_input'];
$filtered_input = mysqli_real_escape_string($connection, $user_input);

Keywords

filter_var htmlspecialchars preg_match filter_input validation

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