使用PHP自带的处理函数获取文件拓展名jpg或者.jpg

$file_name='abc.jpg';
function get_ext1($file_name){
    return strchr($file_name,'.');
}

function get_ext2($file_name){
    return substr($file_name,strpos($file_name,'.'));
}

function get_ext3($file_name){
    $array = explode('.',$file_name);
    return array_pop($array);
}

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

function get_ext5($doc){
    $a = strrev(substr(strrev($doc),0,strpos(strrev($doc),'.')));
    return $a;
}
echo get_ext5($file_name);
echo get_ext4($file_name);
echo get_ext3($file_name);
echo get_ext2($file_name);
echo get_ext1($file_name);