During the switch from Filesystem V2 to V3 I was bit by the new operator<<( basic_ostream<...> ) behaviour. The problem is that in V3 the path gets quoted when being output to the stream (and '&' is used as an escape character). This breaks the invariant which used to hold until now: std::stringstream stream; stream << path; assert( stream.str() == path.string() ); I have made the adjustments to my code, but I find this behaviour a bit surprising and was interested in the rationale for this decision. I could not find it on the Boost Filesystem home page. The only reason I could fathom is so that one can do this: std::stringstream stream; stream << path1 << path2; stream >> path3 >> path4; assert( path1 == path3 ); assert( path2 == path4 ); If so - I know several platforms where this will generally fail, as both & and " are legal characters in file names. Thank you for your response.