DBF: Read columnnames

I use this code to get values from a DBF file:

$db_file = "test.dbf";
dbase_open ($db_file, 2);
$user = dbase_get_record ($db, 1);

Only when I do this I can't get the columnnames from the dbf file.
I also tried to use:
$fieldnames = array_keys($user);
But this gave me numeric values.

Does someone know how I could read the columnnames from a
DBF file?