使用五种以上方式获取一个文件的扩展名

//1)
function get_ext1($file_name)
{
        return strrchr($file_name, '.');
}

//2)
function get_ext2($file_name)
{
        return substr($file_name, strrpos($file_name, '.'));
}

//3)
function get_ext3($file_name)
{
        return array_pop(explode('.', $file_name));
}

//4)
function get_ext4($file_name)
{
        $p = pathinfo($file_name);
        return $p['extension'];
}

//5)
function get_ext5($file_name)
{
        return strrev(substr(strrev($file_name), 0, strpos(strrev($file_name), '.')));
}