How much functionality is “acceptable” for a C++ struct?

Question

My first post so please go easy on me!

I know that there\'s no real difference between structs and classes in C++, but a lot of people including me use a struct or class

Answer 1

Another common use of structs is for template stuff and local RAII or functor classes. These are one-off bits of code that are closer to functions than they are to whole classes, and requiring the extra public: declaration is just silly. If you look at boost, you'll see a lot of stuff like this:

template<
      bool C
    , typename T1
    , typename T2
    >
struct if_c
{
    typedef T1 type;
};

It's clearly not a POD (in fact it doesn't hold any data at all). In other cases you can have RAII class that consist of only a constructor/desctructor:

struct LogOnLeavingScope : public NonCopyable
{
    string Message;
    LogOnLeavingScope(const string &message) : Message(message) {}
    ~LogOnLeavingScope() { Log(Message); }
];

Functor classes would offer the same argument:

struct Logger
{
    void operator()(const string &message) { Log(message); }
}

I'd say there's no one feature of C++ that implies you should use a class instead of a struct (except maybe virtual functions). It's all about what interface you want to present - use a struct if you are ok with everything being public. If you find you are wanting to add private: sections, that a good sign you really want a class instead of a struct.