C / C++ / MFC

Re: empty virtual method good practice question ...

11-Dec-02 9:12

I have

//Base Class
class BaseClass
{
//...
 virtual void SomeMethod();
//...
}

class DerivedClass : public BaseClass
{
//...
 virtual void SomeMethod(); // question will be about this ...
//...
}

class AnotherDerivedClass : public DerivedClass
{
//...
 virtual void SomeMethod();
//...
}

When I call AnotherDerivedClass::SomeMethod(), I will usually also call the base class method :

void AnotherDerivedClass::SomeMethod()
{
// do something locally to the derived class ...
 
  DerivedClass::SomeMethod();
}

in one case of class hierarchy, the middle class ( here DerivedClass ), do nothing more than just call the base class :

void DerivedClass::SomeMethod()
{
// nothing except calling base class.
  BaseClass::SomeMethod();
}

Is it good practice to have the DerivedClass::SomeMethod there ? or can I call BaseClass::SomeMethod() from the AnotherDerivedClass::SomeMethod() ?

The question, is it preferable to explicitly create empty virtual method just to call the base class so that I have a knowledge of the chain of ineritance ? or can I "jump" to the base class without going thrue the middle class if it does nothing ?

Thanks.

Max.

Daniel Turini11-Dec-02 9:15

Daniel Turini

11-Dec-02 9:15

Maximilien wrote:
The question, is it preferable to explicitly create empty virtual method just to call the base class so that I have a knowledge of the chain of ineritance ? or can I "jump" to the base class without going thrue the middle class if it does nothing ?
IHMO, this would introduce an unnecessary overhead, only because you don't use a tool to draw the class hierarchy.

I see dumb people

Re: empty virtual method good practice question ...

Maximilien11-Dec-02 9:25

Re: empty virtual method good practice question ...

11-Dec-02 9:25

Daniel Turini wrote:
this would introduce an unnecessary overhead

I know, but since it's not in a performance critical part of the software ( UI ) I can live with this.

Daniel Turini wrote:
, only because you don't use a tool to draw the class hierarchy.

I don't understand what you mean by that ?

Max.

Ranjan Banerji11-Dec-02 9:23

Ranjan Banerji

11-Dec-02 9:23

If DerivedClass is not going to do anything but call the BaseClass virtual function then why even declare this function in this class.

If AnotherDerived will first do some stuff and then call the BaseClass virtual then you still do not need the function in the DerivedClass.

void AnotherDerivedClass::SomeMethod(){<br />
// do something locally to the derived class ...   <br />
   BaseClass::SomeMethod();  //Do this instead of DerivedClass::SomeMethod()<br />
}<br />

What you choose to do should be based on what the program/design requirements are.

Re: empty virtual method good practice question ...

Alvaro Mendez11-Dec-02 9:26

Re: empty virtual method good practice question ...

11-Dec-02 9:26

Good question. Here's my answer:

1. Your AnotherDerivedClass::SomeMethod can always call DerivedClass::SomeMethod. If DerivedClass does not have it, the compiler will automatically call BaseClass's method.

2. You can certainly call BaseClass::SomeMethod from AnotherDerivedClass. (This isn't allowed in Java, by the way).

3. You only need to have a (dummy) DerivedClass::SomeMethod whenever you have another method of the same name with a different set of parameters. Here's the example:

void DerivedClass::SomeMethod()
{
  // nothing except calling base class.  
  BaseClass::SomeMethod();
}
 
void DerivedClass::SomeMethod(int nParam)
{
  // do something here
}

If you didn't have DerivedClass::SomeMethod() in DerivedClass, the compiler would not allow you to call DerivedClass::SomeMethod, either from AnotherDerivedClass or through an instance of the class.

Regards,
Alvaro

Well done is better than well said. -- Benjamin Franklin
(I actually prefer medium-well.)

Maximilien11-Dec-02 9:30

Re: empty virtual method good practice question ...

11-Dec-02 9:30

Alvaro Mendez wrote:
2. You can certainly call BaseClass::SomeMethod from AnotherDerivedClass. (This isn't allowed in Java, by the way).

I don't know Java ? so, in Java I'd have to call the base class method for each derive class ?

Alvaro Mendez wrote:
If you didn't have DerivedClass::SomeMethod() in DerivedClass, the compiler would not allow you to call DerivedClass::SomeMethod, either from AnotherDerivedClass or through an instance of the class.

Yep! that I know!

Thanks

Max.

Alvaro Mendez11-Dec-02 9:35

Re: empty virtual method good practice question ...

11-Dec-02 9:35

Maximilien wrote:
I don't know Java ? so, in Java I'd have to call the base class method for each derive class ?

Well, in Java you can only refer to the class to which you directly derived from, via the super keyword.

Regards,
Alvaro

Well done is better than well said. -- Benjamin Franklin
(I actually prefer medium-well.)

Maximilien11-Dec-02 9:38

11-Dec-02 9:38

Alvaro Mendez wrote:
Well, in Java you can only refer to the class to which you directly derived from, via the super keyword.

Sounds like Apple's ObjectC language, I have to look at ObjectiveC book tonight!

Max.

Char to INT?

Anonymous11-Dec-02 9:09

Anonymous

11-Dec-02 9:09

Hi.

I have a Char which containes a number, example 32. How do I convert the char to INT?

char cTest[100]="32";
int iTest;

now I want to convert the cTest to iTest so it's a integer instead of a char.

Any function which can do this?

thanks for any info.

Alvaro Mendez11-Dec-02 9:12

11-Dec-02 9:12

atoi.

int iTest = atoi(cTest);

Regards,
Alvaro

Well done is better than well said. -- Benjamin Franklin
(I actually prefer medium-well.)

Nitron11-Dec-02 13:23

Nitron

11-Dec-02 13:23

i'll second that.

also, if you need a double, atof:

double data = atof(szData);

- Nitron

"Those that say a task is impossible shouldn't interrupt the ones who are doing it." - Chinese Proverb

Greven11-Dec-02 9:21

Greven

11-Dec-02 9:21

I think the easiest way would be to simply cast it...

iTest = (int)cTest[i];

Wouldn't that work? Unsure | :~

Programming in binary is as easy as 01 10 11.

Alvaro Mendez11-Dec-02 9:29

11-Dec-02 9:29

Nope, it wouldn't work. Only the first character would be converted, and to it's ASCII value -- which is not what he needs.

Regards,
Alvaro

Well done is better than well said. -- Benjamin Franklin
(I actually prefer medium-well.)

Greven11-Dec-02 10:23

Greven

11-Dec-02 10:23

Ah, my mistake... Didn't see the quote around 32... Thought he had an array of char's, not a string.
Blush | :O

Programming in binary is as easy as 01 10 11.

Christian Graus11-Dec-02 10:03

Christian Graus

11-Dec-02 10:03

I generally bring up a console project and test my theory if I'm not sure about advice I am about to give Smile | :)

Christian

No offense, but I don't really want to encourage the creation of another VB developer. - Larry Antram 22 Oct 2002

C# will attract all comers, where VB is for IT Journalists and managers - Michael P Butler 05-12-2002

Again, you can screw up a C/C++ program just as easily as a VB program. OK, maybe not as easily, but it's certainly doable. - Jamie Nordmeyer - 15-Nov-2002

Catching OnSysCommand in own class

Ravi Bhavnani11-Dec-02 9:39

Ravi Bhavnani

11-Dec-02 9:39

If you don't care about performance Smile | :)

you can do:

sscanf (cTest, "%d", &iTest);

/ravi

Let's put "civil" back in "civilization"
http://www.ravib.com
ravib@ravib.com

In Place Server

Anthony988711-Dec-02 9:00

Anthony9887

11-Dec-02 9:00

I'm having troubles modifying the menus for the ole server once embedded into a container document.

Thanks

BtL2711-Dec-02 8:44

BtL27

11-Dec-02 8:44

Hi,

i think this problem may be easy to answer for you.

I have created my own class:

-header-file:

class CTrayIcon : public CWnd
{
public:
CTrayIcon(); // Konstruktor
virtual ~CTrayIcon(); // Dekonstruktor

int AddTrayIcon(HICON pIcon,int iMenu);
protected:
// Overrides
// ClassWizard generated virtual function overrides
//{{AFX_VIRTUAL(CTrayIcon)
//}}AFX_VIRTUAL
protected:
//{{AFX_MSG(CTrayIcon)
afx_msg void OnSysCommand(UINT nID, LPARAM lParam);
//}}AFX_MSG
DECLARE_MESSAGE_MAP()
};

The Class-Wizard automatically adds the function OnSysCommand to the header and of course to the cpp. Now, i do not know, what i must do, that all messages of the dlg-window(main-dialog-window), especially WM_SYSCOMMAND, can catch in my class ?

Re: Catching OnSysCommand in own class

Alvaro Mendez11-Dec-02 9:04