renaming while uploading??

i had a photo gallery for users where users can upload many photos..
I am writing an script that renames the files while uploading as

$new_filename=$user_id."_"."uniqueNO";
$new_add=$new_filename.".jpg";
rename($old_add,$new_add);
problem??
>how to generate "uniqueNO" that never repeats?
>is there any function??
>this script changes any file extension to .jpg...is that good or else?
Plz help in solving above questions....
Thank U

uploaded files are given a unique name in the tmp directory reachable by $_FILES['nameofthefileinputformelement']['tmp_name']. I don't remember if it keeps the extension or not.

I believe it does keep the extension, but I could be wrong. Also, for a unique id, you could write a functon, or use uniqid() (http://www.php.net/function.uniqid).

My win version of php assigna all files the *.tmp extension.

I threw this into my friends script, which is what you are doing (I think) you can adjust the code obviously, though.


// Grab extension from filename and create random id.
$ext = substr($file_name, strpos($file_name, ".")+1, strlen($file_name));
$new_file_name = substr(md5(uniqid(microtime())), 0, 8).".".$ext;


The random ID part is bigger then it really needs to be, but thats what he originally had, didn't want to mess with it.