locating general file path

[jaymoore_299]

When I want to refer to a file in the main directory I have to use something like this:
$a1=function_name("/usr/www/virtual/username/www.domain.com/file.txt",9);

Since the file is in my main folder for the domain, is there a more general way to refer to the file without writing out all the "/usr/www/virtual/username/" part?

Something like this
$a1=function_name("$_Find_main_domain_path()file.txt",9);

and it would always refer to that particular file in the main directory regardless what domain it is in.

[devinemke]

you can use $_SERVER['DOCUMENT_ROOT'] if available

[jazz_snob]

I often define a constant and put it in the config script that gets included w/ every page:

define( 'DATA', '/path/to/my/data/directory');

then I can say, for example

fopen( DATA . '/myfile', 'a' );

Since its a defined constant I don't have to worry about visibility (scope) using it inside classes or function calls.