Managed C++/CLI

can anybody tell me why the size of an empty class is 1

10-Dec-07 5:11

Another naive poster gets hit with a cold one.

"We make a living by what we get, we make a life by what we give." --Winston Churchill

philiptabraham9-Dec-07 23:19

philiptabraham

9-Dec-07 23:19

can anybody tell me why the size of an empty class is 1.and i also want to know why we cant create an object for an abstract class.

Thanks in advance

Re: can anybody tell me why the size of an empty class is 1 [modified]

George L. Jackson10-Dec-07 3:31

Re: can anybody tell me why the size of an empty class is 1

10-Dec-07 3:31

C++ requires freestanding empty objects to have non-zero size. Most compilers automatically insert a char into "empty" objects to satisfy this. However, if your empty class is a base class then it won't add any size to the derived class object.

See: http://msdn2.microsoft.com/en-us/library/f42z47h2(VS.80).aspx[^]

You cannot create an object directly from an abstract class since it contains virtual method(s) without implementation(s).

"We make a living by what we get, we make a life by what we give." --Winston Churchill

modified on Monday, December 10, 2007 3:25:41 PM

Luc Pattyn10-Dec-07 3:41

Luc Pattyn

10-Dec-07 3:41

Giving them the smallest possible non-zero size makes sure different objects
result in different pointer/reference values, which is what you hope to get isn't it?

Smile | :)

Luc Pattyn [Forum Guidelines] [My Articles]

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Re: can anybody tell me why the size of an empty class is 1 [modified]

Mark Salsbery10-Dec-07 7:59

Mark Salsbery

10-Dec-07 7:59

philiptabraham wrote:
i also want to know why we cant create an object for an abstract class

If you could, the class wouldn't be abstract.

It doesn't make sense to create an object of a class that
has virtual functions that are NULL.

Mark

Mark Salsbery
Microsoft MVP - Visual C++

Java | [Coffee]

modified on Monday, December 10, 2007 3:15:35 PM

Re: can anybody tell me why the size of an empty class is 1

George L. Jackson10-Dec-07 8:36

Re: can anybody tell me why the size of an empty class is 1

10-Dec-07 8:36

Mark Salsbery wrote:
It doesn't make sense to create an object of a class that
doesn't have a complete implementation.

You can make a class non-copyable by declaring a private copy constructor (and assignment operator) without an implementation!

"We make a living by what we get, we make a life by what we give." --Winston Churchill

Mark Salsbery10-Dec-07 9:17

Mark Salsbery

10-Dec-07 9:17

right. badly worded - I changed it a bit. It took a long time
for CP to let me edit it (or reply to you Smile | :)

).

Mark

Mark Salsbery
Microsoft MVP - Visual C++

Java | [Coffee]

MVC Design Pattern - Controller & View problem

atzplzw9-Dec-07 13:55

atzplzw

9-Dec-07 13:55

Hello!

Being new to C++/CLI I'm trying to create a MVC design pattern as a start. Sadly I'm stuck with event management. Here is my code so far:

Controller.h

<br />
#pragma once <br />
#include "Model.h" <br />
#include "View.h" <br />
<br />
public ref class Controller <br />
{ <br />
private: Model^ mainModel; <br />
private: View^ mainView; <br />
<br />
public: Controller(void) { <br />
    mainModel = gcnew Model(); <br />
    mainView = gcnew View(this); <br />
    Application::Run(mainView); <br />
  } <br />
public: System::Void Btn_Open_Click(System::Object^ sender, System::EventArgs^ e) {<br />
    //do something<br />
  }<br />
};<br />

View.h

<br />
#pragma once <br />
//class forward declaration<br />
ref class Controller; <br />
<br />
public ref class View : public System::Windows::Forms::Form <br />
{ <br />
private: Controller^ mainController; <br />
public: View(Controller^ con) { <br />
    mainController = con; <br />
    InitializeComponent(); <br />
  } <br />
InitializeComponent() { <br />
... <br />
this->Btn_Open->Click += gcnew System::EventHandler(this, &mainController::Btn_Open_Click);<br />
...<br />
} <br />

With MCV the controller is responsible for event managment. That's why I choose to create the View with a reference to the controller.
But now I'm stuck with the EventHandler. The code above compiles fine when the last line is commented out. Of course, then there is no event handler.

So what is the correct way to do this? I just want the EventHandler in the View class to call a method in another class. How to do that?

Thanks for your help and suggestions!

Re: MVC Design Pattern - Controller & View problem

George L. Jackson10-Dec-07 14:03

Re: MVC Design Pattern - Controller & View problem

10-Dec-07 14:03

Windows Forms is based partially on MVC design pattern but it is not a pure implementation of it. Thus, you are doomed in implementing MVC with it as your base.

"We make a living by what we get, we make a life by what we give." --Winston Churchill

led mike11-Dec-07 6:56

led mike

11-Dec-07 6:56

atzplzw wrote:
With MCV the controller is responsible for event managment.

Other patterns can be introduced into the MVC design like a Command Pattern. Strictly speaking your controller class does NOT have to be directly hooked to the event of the user interface control.

Also have you seen this[^]?

[Message Deleted]

rogery9-Dec-07 0:28

rogery

9-Dec-07 0:28

[Message Deleted]

Luc Pattyn9-Dec-07 7:13

Luc Pattyn

9-Dec-07 7:13

Hi,

there is an "as" operator that returns either a new reference of the indicated type,
or a null value. Example:

public: Int32 __gc* Compare(Object __gc* object1, Object __gc* object2)
{
    ProcessModule __gc* module1 = (object1 as ProcessModule);
    ProcessModule __gc* module2 = (object2 as ProcessModule);
    return String::Compare(module1->FileName, module2->FileName, true);
}

BTW: the above is Reflector output of an assembly based on C# code.

Smile | :)

Luc Pattyn [Forum Guidelines] [My Articles]

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George L. Jackson9-Dec-07 11:25

9-Dec-07 11:25

C++/CLI does not have an "as" operator like C#. You have to use dynamic_cast or static_cast.

"We make a living by what we get, we make a life by what we give." --Winston Churchill

Luc Pattyn9-Dec-07 12:13

Luc Pattyn

9-Dec-07 12:13

Hi George,

indeed, I have no reference to the "as" keyword in C++, except for the fact
that Reflector uses it. Confused | :confused:

MSDN itself shows how to use casts to simulate C#'s as, as you indicated.

Smile | :)

Luc Pattyn [Forum Guidelines] [My Articles]

Sorry for any delays in replying, I currently don't get e-mail notifications.

George L. Jackson9-Dec-07 11:33

Subclassing a window and not getting all the messages

9-Dec-07 11:33

You can use dynamic_cast:

if (dynamic_cast<TextBox^>(control) != nullptr) // works like the C# is operator
{
  // "control" is a TextBox control.
}

"We make a living by what we get, we make a life by what we give." --Winston Churchill

Dave Calkins7-Dec-07 17:32

Dave Calkins

7-Dec-07 17:32

We're interested in subclassing a window in order to handle window messages (specifically mouse click and movement).

Our current approach is to derive a listener class from NativeWindow, assign it the handle to the window in question, and then set up a message handler to handle the incoming messages.

The behavior we’re seeing is that only a very few windows messages come down to our listener class. (Mainly WM_NCHITTTEST).

Any ideas?

Manage Visual C++.NET to C#.NET

jimmy2shoes7-Dec-07 13:39

jimmy2shoes

7-Dec-07 13:39

Hi fellas

I have a program that is currently wrote in Managed C++ within the MS Visual Studio 2005 environment i was wondering if there is anyway i can migrate it to C#.NET without having to re-code it?

Any help would be majorly appricated fellas

thanks

Dave Doknjas7-Dec-07 14:23

Dave Doknjas

7-Dec-07 14:23

Our C++ to C# Converter utility will get you part of the way there (there will be some adjustments you'll have to make, but the conversion quality is pretty good for Managed C++ or C++/CLI).

David Anton
http://www.tangiblesoftwaresolutions.com
C++ to C# Converter
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C++ to Java Converter
C++ to C++/CLI Converter
Instant C#: VB to C# converter
Instant VB: C# to VB converter
Instant C++: converts C# to C++/CLI and VB to C++/CLI

jimmy2shoes8-Dec-07 0:41

jimmy2shoes

8-Dec-07 0:41

i have been looking at that one mate, i have a good part of it converted by doing it myself and using that software above, only problem is i do not knonw the difference between .CPP files and .h files. there is some of them in my project with the same name for example game.h and game.cpp how would i encorporate them into one c# class??

thanks and sorry for being niave, not a big user of c++

thanks again

Dave Doknjas8-Dec-07 2:53

Dave Doknjas

8-Dec-07 2:53

'C++ to C# Converter' takes care of that. During the conversion, it automatically merges the header file with the same name into the conversion input (in C++, '#include' just inputs the file at the location of the #include before compilation).

jimmy2shoes9-Dec-07 5:26

jimmy2shoes

9-Dec-07 5:26

what happens if there is two header files, i can only select one at a time

thanks