virtual-functions

问题 Like the title says, e.g. does having 8 derived classes with virtual functions affect performances more than having 2 derived classes? And if so, is the difference negligible? And what about multiple inheritance (non virtual inheritance)? Thanks in advance. 回答1: The common implementation of dynamic dispatch in C++ is by means of a virtual table, which is basically an array of pointers to functions, one for each virtual function in the type. The length of the inheritance chain does not matter,

问题 This question already has answers here : Closed 8 years ago . Possible Duplicate: class has virtual functions and accessible non-virtual destructor I got this code from following a tutorial by thenewboston: #include <iostream> using namespace std; class Enemy { public: virtual void attack(){}; }; class Ninja: public Enemy { public: void attack(){ cout << "ninja attack"<<endl; } }; class Monster: public Enemy { public: void attack(){ cout << "monster attack"<<endl; } }; int main() { Ninja n;

问题 Calling virtual methods in C++ is prohibited, however there are a few situations, where it might be very useful. Consider the following situation - pair of Parent and Child classes. Parent constructor requires a Child class to be instantiated, because it has to initialize it in a special way. Both Parent and Child may be derived, such that DerivedParent uses DerivedChild. There's a problem, however - because in Parent::ctor call from DerivedParent::ctor, base class should have an instance of

问题 Suppose I have a pair of base classes: class A {}; class B { virtual void foo(A* ref); virtual void foo2(A* ref); }; And from them, a few derived classes: class C : virtual public A { int data; }; class D : public B { virtual void foo(A* ref) { ((C*) (ref)).data = 5; } }; class E : virtual public A { int otherData; }; class F : public B { virtual void foo2(A* ref) { ((E*) (ref)).otherData = 6; } }; And finally, we have a class that follows suit, as such: class G : public E, public C { }; with

问题 To begin, I am trying to write a run-of-the-mill, simple Ray Tracer. In my Ray Tracer, I have multiple types of geometries in the world, all derived from a base class called "SceneObject". I've included the header for it here. /** Interface for all objects that will appear in a scene */ class SceneObject { public: mat4 M, M_inv; Color c; SceneObject(); ~SceneObject(); /** The transformation matrix to be applied to all points of this object. Identity leaves the object in world frame. */ void

问题 We can't create an object of an abstract class, right? So how can I call a virtual function which has definition in both abstract base class and derived class? I want to execute the code in abstract base class but currently, I am using derived class's object. class T { public: virtual int f1()=0; virtual int f2() { a = 5; return a } } class DT : public T { public: int f1() { return 10; } int f2() { return 4; } } int main() { T *t; t = new DT(); ............ } Is there any way I can call the

问题 although I've been helped countless times by other questions/answers here, this is my first question here, so don't be too harsh on me! :) I've been learning QT/C++ and let's assume I have something like this: class AbstractMasterClass{ public: virtual void foo(void) = 0; //Pure virtual method } This class will have plenty subclasses, each one of them implementing their own foo() method. And the question is: How can I create a QList which I'll populate with AbstractMasterClass's subclasses?

问题 Consider the following code in C++17: #include <iostream> #include <functional> struct base { base() {std::cout << "base::base" << std::endl;} virtual ~base() {std::cout << "base::~base" << std::endl;} virtual void operator()() {std::cout << "base::operator()" << std::endl;} }; struct derived1: base { derived1() {std::cout << "derived1::derived1" << std::endl;} virtual ~derived1() {std::cout << "derived1::~derived1" << std::endl;} virtual void operator()() {std::cout << "derived1::operator()"

问题 First off I apologize if there is another post out there that answers this, all the similar posts I found dealt with diamond inheritance schemes or defined functions, which this does not. In short, I'm wondering if it is possible to have one class inherit from two other classes where both child classes has a function with the same name and arguments but it is defined in one child class, and pure-virtual in another. Furthermore if I can do this, would invoking the function on the pure-virtual

问题 Consider the following code segment: class Window // Base class for C++ virtual function example { public: virtual void Create() // virtual function for C++ virtual function example { cout <<"Base class Window"<<endl; } }; class CommandButton : public Window { public: void Create() { cout<<"Derived class Command Button - Overridden C++ virtual function"<<endl; } }; int main() { Window *button = new CommandButton; Window& aRef = *button; aRef.Create(); // Output: Derived class Command Button -