Hi. I'm attaching a patch for libs/iostreams/src/mapped_file.cpp which corrects the mapped_file_source::operator!() operator. It seems to have been erroneously returning true in case the implementation object exists but has its error_ flag set. Hope this helps. Best regards, Jurko Gospodnetić Index: libs/iostreams/src/mapped_file.cpp =================================================================== --- libs/iostreams/src/mapped_file.cpp (revision 46155) +++ libs/iostreams/src/mapped_file.cpp (working copy) @@ -150,7 +150,7 @@ } bool mapped_file_source::operator!() const -{ return !!pimpl_ || pimpl_->error_; } +{ return !pimpl_ || pimpl_->error_; } BOOST_IOS::openmode mapped_file_source::mode() const { return pimpl_->mode_; }