in C++ , can i create a explicit constructor with all default arguments

i am using VS 2013.

class A{
public:
  std::wstring key;

private:
 explicit A(const std::wstring& k = L"", bool bCondition = false );
}

Its compiling , but failing with below error :

error LNK2001: unresolved external symbol "private: __thiscall A::A(class std::basic_string,class std::allocator > const & ....