c++ - Stringstream error: cannot access private member declared in class 'std::basic_ios<_Elem,_Traits>' -

in creating simple exception class extension (where can construct error messages more easily), i've isolated error down following simple code:

#include <sstream> #include <string> class mycout { public:     std::stringstream ssout;    // removing gets rid of error     template <typename t> mycout& operator << (const t &x) {         // formatting         return *this;     } };  class myerr : public mycout { public:     using mycout::operator<<; };  int main(int argc, const char* argv[]) {     throw myerr() << "errormsg" << 1;     mycout() << "message formatted";     return 0; } 

which, on compiling, produces error:

1>c:\program files (x86)\microsoft visual studio 10.0\vc\include\sstream(724): error c2248: 'std::basic_ios<_elem,_traits>::basic_ios' : cannot access private member declared in class 'std::basic_ios<_elem,_traits>' 1>          1>          [ 1>              _elem=char, 1>              _traits=std::char_traits<char> 1>          ] 1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\ios(176) : see declaration of 'std::basic_ios<_elem,_traits>::basic_ios' 1>          1>          [ 1>              _elem=char, 1>              _traits=std::char_traits<char> 1>          ] 1>          diagnostic occurred in compiler generated function 'std::basic_stringstream<_elem,_traits,_alloc>::basic_stringstream(const std::basic_stringstream<_elem,_traits,_alloc> &)' 1>          1>          [ 1>              _elem=char, 1>              _traits=std::char_traits<char>, 1>              _alloc=std::allocator<char> 1>          ] 

(in actual fact it's more complex , extends stuff std::runtime_error)

i have seen previous answers state problem arises not passing streams reference, can't see how i'm not.

commenting out std::stringstream ssout fixes issue. why, , how fix underlying problem?

you're throwing exception value, indeed recommended practice. however, means exception gets copied part of throw statement, must have accessible copy constructor. , because have non-copyable member (std::stringstream), must provide own copy ctor.