I have also needed this functionality. It is my belief that there is no such functionality in Boost.Filesystem. I have coded simple routine that works on the tiny subset of platforms and filesystems that I am currently targeting. I find that I need this functionality frequently. I would like to see such functionality added to Boost.Filesystem. I'm pretty sure that there are enormous difficulties when one considers symbolic links etc. However perhaps if the difficulties in addressing these challenges prove to be insurmountable we could provide an implementation with some strong pre-conditions.
 

Regards,
Neil Groves