Model-View-Controller Explained in C++

5 Comments

1. Damien Rogé

   The View never render anything in your exemple as the Render() function is not the callback given to the model.
   Also, the MVC diagram shows no links between the Model and the View, but in your code the is a strong coupling between these two.
   Am I misunderstanding something ?

   Reply
2. Liam

   Could you explain what the function pointers are doing here? I’m having trouble understanding 1: the typedef syntax in common.h and 2: the purpose of the function pointer in mvc.cpp (and wherever else it is used).

   Reply
3. JC

   Hi ! Thanks for this tutorial.

   As in the previous comment, I also see that “issue” and I changed the code to get only a constant pointer to the model in the view (cf. following code). Therefore, the view doesn’t have a copy of the model and the data always match.

   Does it still respect the MVC design pattern ?
   Maybe, having a copy of the model in the view can also allow some “rendering processing”. For example, having a model which holds a real signal (array of reals), the view can implement a FFT visualization of the corresponding spectrum.

   ——- code ——
   // https://helloacm.com/model-view-controller-explained-in-c/

   #include
   #include
   using namespace std;

   // common.h
   typedef void (*DataChangeHandler)(string newData);

   // model.h
   // Model is responsible for data get and set
   class Model {
   public:
   Model(const string &data) {
   this->SetData(data);
   }
   Model() { } // default constructor
   string Data() const {
   return this->data;
   }

   void SetData(const string &data) {
   this->data = data;
   if (this->event != nullptr) { // data change callback event
   this->event(data);
   }
   }
   // register the event when data changes.
   void RegisterDataChangeHandler(DataChangeHandler handler) {
   this->event = handler;
   }
   private:
   string data = “”;
   DataChangeHandler event = nullptr;
   };

   // view.h
   // View is responsible to present data to users
   class View {
   public:
   View(const Model &model) {
   this->model = &;
   }
   View() {}
   void SetModel(const Model &model) {
   this->model = &;
   }
   void Render() {
   std::cout << "Model Data = " <Data() < no need to update the data held by the
   * view…
   */
   };

   // controller.h
   // Controller combines Model and View
   class Controller {
   public:
   Controller(const Model &model, const View &view) {
   this->SetModel(model);
   this->SetView(view);
   }
   void SetModel(const Model &model) {
   this->model = model;
   }
   void SetView(const View &view) {
   this->view = view;
   }
   // when application starts
   void OnLoad() {
   this->view.Render();
   }
   private:
   Model model;
   View view;
   };

   // mvc.cpp

   void DataChange(string data) {
   cout << "Data Changes: " << data <<endl;
   }

   int main() {
   Model model("Model");
   View view(model);
   // register the data-change event
   model.RegisterDataChangeHandler(&;DataChange);
   // binds model and view.
   Controller controller(model, view);
   // when application starts or button is clicked or form is shown…
   controller.OnLoad();
   model.SetData("Changes"); // this should trigger View to render
   controller.OnLoad();
   return 0;
   }

   Reply
4. QQ

   Hi ! Nice tutorial but I think the C++ code has issue but maybe I’m wrong.

   1/ If you change a little your code
   controller.OnLoad();
   model.SetData(“Changes”);
   return 0;

   By:
   controller.OnLoad();
   model.SetData(“Changes”);
   controller.OnLoad();
   return 0;

   You will see the issue ! The display is:
   Model Data = Model
   Data Changes: Changes
   Model Data = Model

   Instead of:
   Model Data = Model
   Data Changes: Changes
   Model Data = Changes

   2/ The problem is that you call constructors by copy instead of using reference. or address. Replace for example:
   private:
   Model model;
   View view;
   For:
   private:
   Model *model;
   View *view;
   And:
   void SetView(const View &view) {
   this->view = view;
   }
   By:
   void SetView(const View &view) {
   this->view = &view;
   }
   An so long for other classes and methods.

   Reply
   • ACMer

     Thanks! You may be right.
     The purpose of this post is to illustrate the idea of MVC, but thanks for the suggestions

     Reply