PHP: Check that characters in a variable are alpha numeric using ereg

<?php
// Example 1
$text = "onlyalphanumericcharacters012345";
if (ereg('[^A-Za-z0-9]', $text))
{ 
      echo "This contains characters other than letters and numbers";
}
else { 
       echo "This contains only letters and numbers";   
}

// Example 2
$text = "mixedcharacters012345&../@";
if (ereg('[^A-Za-z0-9]', $text))
{
     echo "This contains characters other than letters and numbers";
}
else {
     echo "This contains only letters and numbers";   
}
?>