preprocessor callbacks

   I am implementing a preprocessor callback. I use the virtual function
InclusionDirective( .. , ..) to stop whenever a #include is found. What I
want is to stop whenever a new file is entered and get the location of the
first line in that file. I tried using FileChanged() and checked
FileChangeReason == EnterFile but it stops at some unexpected locations too.
Is there a way to find the first location of the first line of the file
being included when you stop at InclusionDirective?