<!DOCTYPE html>
<html>
<body>
<?php
$str = 'one,two,three,four';
// 零 limit
print_r(explode(',',$str,0));
// 正的 limit
print_r(explode(',',$str,2));
// 负的 limit
print_r(explode(',',$str,-1));
?>
</body>
</html>