virtual-functions

I have two classes: class x { public: virtual void hello() { std::cout << "x" << std::endl; } }; class y : public x { public: void hello() { std::cout << "y" << std::endl; } }; Can someone explain why the following two calls to hello() print different messages? Why don't they both print "y"? Is it because the first one is a copy while the second one actually points to the object in memory? int main() { y a; x b = a; b.hello(); // prints x x* c = &a; c->hello(); // prints y return 0; } Yes, you are right x b = a; Invokes a copy constructor (b IS an 'x') x& b = a; Assigns a reference and will

I'm getting a runtime error ("memory can't be written") that, after inspection through the debugger, leads to the warning in the tittle. The headers are the following: componente.h: #ifndef COMPONENTE_H #define COMPONENTE_H using namespace std; class componente { int num_piezas; int codigo; char* proovedor; public: componente(); componente(int a, int b, const char* c); virtual ~componente(); virtual void print(); }; #endif // COMPONENTE_H complement.h implementation #include "Componente.h" #include <string.h> #include <iostream> componente::componente() { num_piezas = 0; codigo = 0; strcpy

I have a bunch of systems, lets call them A, B, C, D, E, F, G, H, I, J . They all have similar methods and properties. Some contain the exact same method and properties, some may vary slightly and some may vary a lot. Right now, I have a lot of duplicated code for each system. For example, I have a method called GetPropertyInformation() that is defined for each system. I am trying to figure out which method would be the best approach to reduce duplicate code or maybe one of the methods below is not the way to go: Interface public Interface ISystem { public void GetPropertyInformation(); /

I have this code: class Class { public: virtual void first() {}; virtual void second() {}; }; Class* object = new Class(); object->first(); object->second(); delete object; that I compile with Visual C++ 10 with /O2 and have this disassembly: 282: Class* object = new Class(); 00403953 push 4 00403955 call dword ptr [__imp_operator new (4050BCh)] 0040395B add esp,4 0040395E test eax,eax 00403960 je wmain+1Ch (40396Ch) 00403962 mov dword ptr [eax],offset Class::`vftable' (4056A4h) 00403968 mov esi,eax 0040396A jmp wmain+1Eh (40396Eh) 0040396C xor esi,esi 283: object->first(); 0040396E mov eax

I have a confusion about the inheriting the virtual property of a method. Let's suppose we have 4 classes: class A, class B, class C and class D. The classes are inherited by this way: A -> B -> C -> D, where A is the base class. By this time, I'm sure about this: Beginning the class method declaration with virtual in a base class (class A), makes the method virtual for all classes derived from the base class, including the derived ones of the derived classes. (B and C class methods determined to be virtual). The confusion is here. What if, in the base class A, there wouldn't be any virtual

I have a question, here are two classes below: class Base{ public: virtual void toString(); // generic implementation } class Derive : public Base{ public: ( virtual ) void toString(); // specific implementation } The question is: If I wanna subclass of class Derive perform polymophism using a pointer of type Base , is keyword virtual in the bracket necessary? If the answer is no, what's the difference between member function toString of class Derive with and without virtual? C++03 §10.3/2: If a virtual member function vf is declared in a class Base and in a class Derived, derived directly or

I'm aware that a params modifier (which turns in one parameter of array type into a so-called "parameter array") is specifically not a part of the method signature. Now consider this example: class Giraffid { public virtual void Eat(int[] leaves) { Console.WriteLine("G"); } } class Okapi : Giraffid { public override void Eat(params int[] leaves) { Console.WriteLine("O"); } } This compiles with no warnings. Then saying: var okapi = new Okapi(); okapi.Eat(2, 4, 6); // will not compile! gives an error( No overload for method 'Eat' takes 3 arguments ). Now, I know that the compiler translates the

Why does this happen? http://coliru.stacked-crooked.com/a/e1376beff0c157a1 class Base{ private: virtual void do_run() = 0; public: void run(){ do_run(); } }; class A : public Base { public: // uplift ?? virtual void do_run() override {} }; int main() { A a; a.do_run(); } Why can I override a PRIVATE virtual method as public? According to https://en.cppreference.com/w/cpp/language/virtual#In_detail overwriting a base's virtual member function only care about the function name, parameters, const/volatile-ness and ref qualifier. It doesn't care about return type, access modifier or other things

I'm trying for half an eternity now overriding QWidgets keyPressEvent function in QT but it just won't work. I've to say i am new to CPP, but I know ObjC and standard C. My problem looks like this: class QSGameBoard : public QWidget { Q_OBJECT public: QSGameBoard(QWidget *p, int w, int h, QGraphicsScene *s); signals: void keyCaught(QKeyEvent *e); protected: virtual void keyPressEvent(QKeyEvent *event); }; QSGameBoard is my QWidget subclass and i need to override the keyPressEvent and fire a SIGNAL on each event to notify some registered objects. My overridden keyPressEvent in QSGameBoard.cpp