php在目录中创建文件

The below code checks for a directory 'dat'; if it ins't there, it creates one. That part works just fine; what I need is for it to write a file to said directory where AJAX can read it from.

Here's the php...

//checks for 'dat' directory; if false, creates it, if true, does nothing.
$dir = 'c:\wamp\www\dat';
if(file_exists($dir)){
return;
}
else{
mkdir ('C:\wamp\www\dat',0700);
}
//writes chats to file
$data = fopen($dir. "/chatlog". date('d'). '.txt', 'a+');
fwrite($data, $speak);
fclose($data);
}

And here's the AJAX; I don't need as much help here as I do above, but I won't complain if you provide the help for the AJAX below, mainly in getting it to read from the file within the 'dat' directory...

xhr.open("GET","chatlog<?php /*stamps the chatlog file with date (numerical day only)*/ echo     date("d");?>.txt",true);

Your PHP script is running inside www, then, your file you be created there.

If you want to create the file inside the directory www/dat, just change this line

$file = "chatlog". date('d'). ".txt";

for this one

$file = 'dat\chatlog'. date('d'). '.txt';