如何用PHP正则表达式验证输入字符串是否为IPv4地址格式

$ipv4_regex = "/^([01]?[0-9]{1,2}|2[0-4][0-9]|25[0-5]).([01]?[0-9]{1,2}|2[0-4][0-9]|25[0-5]).([01]?[0-9]{1,2}|2[0-4][0-9]|25[0-5]).([01]?[0-9]{1,2}|2[0-4][0-9]|25[0-5])$/";

function validate_ipv4_address($ipv4_string) {
  $ipv4_regex = "/^([01]?[0-9]{1,2}|2[0-4][0-9]|25[0-5]).([01]?[0-9]{1,2}|2[0-4][0-9]|25[0-5]).([01]?[0-9]{1,2}|2[0-4][0-9]|25[0-5]).([01]?[0-9]{1,2}|2[0-4][0-9]|25[0-5])$/";
  return preg_match($ipv4_regex, $ipv4_string);
}

// Example usage:
$valid_ipv4_address = "192.168.1.1";
$invalid_ipv4_address = "192.168.1.333";

if(validate_ipv4_address($valid_ipv4_address)) {
  echo "$valid_ipv4_address is a valid IPv4 address";
} else {
  echo "$valid_ipv4_address is not a valid IPv4 address";
}

if(validate_ipv4_address($invalid_ipv4_address)) {
  echo "$invalid_ipv4_address is a valid IPv4 address";
} else {
  echo "$invalid_ipv4_address is not a valid IPv4 address";
}