i can create a class with std::string in managed c++ with no problem. however when i try to use std::string in a managed c++ dll, i get the following errors. why is this?'std' : is not a class or namespace name

i added inlcude iostream, but i get a load of other errors if i do this:LINK : error LNK2020: unresolved token (0A000007) _CxxThrowException
LINK : error LNK2020: unresolved token (0A000015) delete
LINK : fatal error LNK1120: 2 unresolved externals