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Hallo, is there some easy way in C++ to tell (in compile-time) if a class/struct has no data members? E.g. struct T{}; My first thought was to compare sizeof(T)==0 , but this always seems to be at least 1. The obvious answer would be to just look at the code, but I would like to switch on this. Konrad Rudolph Since C++11, you can use standard std::is_empty trait: https://en.cppreference.com/w/cpp/types/is_empty If you are on paleo-compiler diet, there is a trick: you can derive from this class in another empty and check whether sizeof(OtherClass) == 1 . Boost does this in its is_empty type

I want to access a member of the MainFragment class from PersonAdapter class but none of them are available. I tried making both the classes and the members public and private also but so far nothing worked. I guess I'm missing something obvious but I just can't figure it out. class MainFragment : Fragment() { lateinit var personAdapter: PersonAdapter lateinit var personListener: OnPersonSelected private var realm: Realm by Delegates.notNull() lateinit var realmListener: RealmChangeListener<Realm> override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState:

In C++, why is private the default visibility for members of classes, but public for structs? C++ was introduced as a superset of C. Structs were carried over from C, where the semantics of their members was that of public. A whole lot of C code exists, including libraries that were desired to work with C++ as well, that use structs. Classes were introduced in C++, and to conform with the OO philosophy of encapsulation, their members are private by default. a_m0d Because a class is a usual way of doing object orientation, which means that member variables should be private and have public

I'm new to C++ and from what I learned so far when you call delete on a pointer that points to something created on the heap then whatever is pointed by that pointer gets erased and the memory is freed, right? However when I tried this on a simple class: class MyClass { int _Id; public: MyClass(int id) : _Id(id) { std::cout << "$Constructing the damn thing! " << _Id << std::endl; } ~MyClass() { std::cout << "?Destructing the damn thing! " << _Id << std::endl; } void Go_XXX_Your_Self() { std::cout << "%OooooooooO NOOOOOO! " << _Id << std::endl; delete this; } void Identify_Your_Self() { std:

Why on earth does the following piece of code work? struct A { std::vector<A> subAs; }; A is an incomplete type, right? If there was a vector of A*s I would understand. But here I don't understand how it works. It seems to be a recursive definition. WhiZTiM This paper was adopted into C++17 which allows incomplete types to be used in certain STL containers. Prior to that, it was Undefined Behavior. To quote from the paper: Based on the discussion on the Issaquah meeting, we achieved the consensus to proceed* with the approach – “Containers of Incomplete Types”, but limit the scope to std:

I have the following problem. I have a function from an external library (which cannot be modified) like this: void externalFunction(int n, void udf(double*) ); I would like to pass as the udf function above a function member of an existing class. Please look at the following code: // External function (tipically from an external library) void externalFunction(int n, void udf(double*) ) { // do something } // User Defined Function (UDF) void myUDF(double* a) { // do something } // Class containing the User Defined Function (UDF) class myClass { public: void classUDF(double* a) { // do