mysqli_real_escape_string() expects parameter 1 to be mysqli, null given code example

Example: mysqli_real_escape_string() expects parameter 1 to be mysqli

$con=mysqli_connect("xxx","xxx","xxx","xxx");

// Check connection
if (mysqli_connect_errno())
  {
  echo "Failed to connect to MySQL: " . mysqli_connect_error();
 }
// pass $con to mysqli_escape_string() function 
$name = mysqli_real_escape_string(trim($_POST["name"]), $con);