当我声明一个类为其他类的成员时，我得到一个错误。错误:在声明朋友时必须使用类键。

I am a C++ rookie and I was experimenting with boost serialization and I wanted to see if it works when a class is declared as a member of another class. But when I compile my code I get loads of errors. I tried declaring baseds as a struct but no change in errors. My code :I am a C++ rookie and I was experimenting with