REF: replace const char* with std::string

git-svn-id: https://www.nitrc.org/svn/cmtk/trunk@4835 42a5c34f-2066-0410-bec5-ba365beb4995
FIX: replace uninitialized const char* with std::string

git-svn-id: https://www.nitrc.org/svn/cmtk/trunk@4836 42a5c34f-2066-0410-bec5-ba365beb4995