DCMTK

Complete DCMTK implementation of <system_error> by implementing OFerror_condition compatible to std::error_condition and defining the respective error code constants (at least the subset that is used by DCMTK). Afterwards replace all occurences of platform specific error constants (e.g. EINTR/WSAEINTR) by converting the error code to an error condition that can then be compared with the respective platform independent constant.