C / C++ / MFC

Re: Sir, Why Virtual Constructor doesn't exist ? Whereas we have virtual Destructor.

1-Aug-06 4:45

if you know what virtual is made for, you would understand that the behavior of a type constructor shouldn't (actually, cannot) be changed/overriden by a child...

on the other side, destructors should always be virtual, so that when destructing a variable, it starts by the child destruction, and then, the base class destruction...

TOXCCT >>> GEII power

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Zac Howland1-Aug-06 4:55

Zac Howland

1-Aug-06 4:55

toxcct wrote:
on the other side, destructors should always be virtual

Not always, just any time you are writing a class that is meant (or allows for) a class to be derived from it. The STL containers do not have virtual destructors because they are not meant to be base classes.

Basically, any time you have a virtual function in your class, you should declare your destructor as virtual.

As for the OP ... the way constructors work does not provide a need for virutal constructors. When an object is created, its allocation is started from the most base class and then works down towards the desired derived class. In other words, if you have a heirarchy where A is derived from B is derived from C, and you declare a variable of type A, the constructor for C is called, then B, and finally A.

If you decide to become a software engineer, you are signing up to have a 1/2" piece of silicon tell you exactly how stupid you really are for 8 hours a day, 5 days a week

Zac

Re: Sir, Why Virtual Constructor doesn't exist ? Whereas we have virtual Destructor.

toxcct1-Aug-06 4:59

Re: Sir, Why Virtual Constructor doesn't exist ? Whereas we have virtual Destructor.

1-Aug-06 4:59

Zac Howland wrote:
Not always, just any time you are writing a class that is meant (or allows for) a class to be derived from it. The STL containers do not have virtual destructors because they are not meant to be base classes.

Basically, any time you have a virtual function in your class, you should declare your destructor as virtual.

actually, this is what i meant. you're not obliged to put every dtors virtual, but as there's no pb to declare them virtual if their class is not derived, and as they should be virtual when the class is derived, then, ,it's more easy to always declare a destructor virtual... Wink | ;)

TOXCCT >>> GEII power

[VisualCalc 3.0 updated ][Flags Beginner's Guide new! ]

Zac Howland1-Aug-06 5:11

Zac Howland

1-Aug-06 5:11

toxcct wrote:
actually, this is what i meant. you're not obliged to put every dtors virtual, but as there's no pb to declare them virtual if their class is not derived

The only problem is that if there are no derived classes (or your class is not meant to allow for derived classes), it is a HUGE overhead to declare it virtual (which causes a v-table to be created for that object).

If you decide to become a software engineer, you are signing up to have a 1/2" piece of silicon tell you exactly how stupid you really are for 8 hours a day, 5 days a week

Zac

Re: Sir, Why Virtual Constructor doesn't exist ? Whereas we have virtual Destructor.

Warren Stevens1-Aug-06 5:13

Warren Stevens

1-Aug-06 5:13

Zac Howland wrote:
Basically, any time you have a virtual function in your class, you should declare your destructor as virtual.

I've always thought of this as a defect in C++, and yet another reason for people to say (rightly in this case) that C++ is too complex.

For legacy-code reasons it's probably too late now, but it really should have been an error if you 1) add a virtual function 2) write a destructor and not make it virtual.

Sigh | :sigh:

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Re: Sir, Why Virtual Constructor doesn't exist ? Whereas we have virtual Destructor.

toxcct1-Aug-06 5:19

Re: Sir, Why Virtual Constructor doesn't exist ? Whereas we have virtual Destructor.

1-Aug-06 5:19

matter of performances...

BTW, you'd better know what you do when you code, complex is the language or not Wink | ;)

TOXCCT >>> GEII power

[VisualCalc 3.0 updated ][Flags Beginner's Guide new! ]

Zac Howland1-Aug-06 5:23

Zac Howland

1-Aug-06 5:23

Warren D Stevens wrote:
I've always thought of this as a defect in C++, and yet another reason for people to say (rightly in this case) that C++ is too complex.

For legacy-code reasons it's probably too late now, but it really should have been an error if you 1) add a virtual function 2) write a destructor and not make it virtual.

I've never really had a problem with this (and I have always failed to see why others have a problem with it). If you declare a function virtual in your class, make your destructor virtual as well. If you have no virtual functions, no need to declare your destructor virtual. I can't remember if Microsoft's compiler does this, but I do know that Intel's and GNU both give you a warning (when you have your warning level set to the highest setting) if you have a class with a virtual member function and no virtual destructor.

It should not be an error because it is valid (as far as the standard is concerned), but it is bad practice since it causes lots of bugs. If you made this into an error, you would have to do the same for things like using new without a corresponding delete.

If you decide to become a software engineer, you are signing up to have a 1/2" piece of silicon tell you exactly how stupid you really are for 8 hours a day, 5 days a week

Zac

Re: Sir, Why Virtual Constructor doesn't exist ? Whereas we have virtual Destructor.

David Crow1-Aug-06 4:56

David Crow

1-Aug-06 4:56

CodeVarma wrote:
Why Virtual Constructor doesn't exist ?

Virtual implies partial information. In other words, only the interface is known as opposed to the exact object type. You need complete information about an object in order to create it.

"Money talks. When my money starts to talk, I get a bill to shut it up." - Frank

"Judge not by the eye but by the heart." - Native American Proverb

Tab Control using 'CTabCtrl'?

Andy Rama1-Aug-06 4:39

1-Aug-06 4:39

Hi to all,
How I can use "Tab Control" in a Dialog?
I had searched for it, but the method was to create a new Class inherited from 'CTabCtrl'.
Can't I use simple Member Variable for "Tab Control" of 'CTabCtrl' type in that Dialog?

Thanks & Best Regards,
Aniket Salunkhe

Hamid_RT1-Aug-06 4:53

1-Aug-06 4:53

Hope I understood your question
you can insert a tab from ToolBax in your form and declare a variable for it and now you can use from it and see http://www.codeproject.com/tabctrl/(General)[^]

WhiteSky

Andy Rama1-Aug-06 20:32

1-Aug-06 20:32

WhiteSky wrote:
Hope I understood your question

Take an example that in Dialog I have a ComboBox 'IDC_COMBO1'. Let member variable attached to it is 'm_cmbCombo1' of 'CComboBox' Class. So to add data in it we can directly use AddString(), InsertString(),..etc.

Similary can't I use a Member variable 'm_tabTab1' of 'CTabCtrl' Class( for a Tab Control) to AddPages & other operation using help of other classes like 'CPropertyPage', 'CPropertySheet',..

'CTabCtrl' has a methods, InsertItem() & other. So using that methods only, can't I use Tab Control ( OR add Dialogs to Tab Control)....instead of Inheriting a new Class from 'CTabCtrl'.

Hamid_RT2-Aug-06 9:29

2-Aug-06 9:29

I dont understand Is your problem CTabCtrl that you cant insert items to it?

WhiteSky

Andy Rama2-Aug-06 21:04

2-Aug-06 21:04

ya, ( how to insert Dialog using Member Fubctions of CTabCtrl Class? )

Hamid_RT2-Aug-06 22:01

2-Aug-06 22:01

See

<br />
//you dont need to create if you enter from toolbox<br />
m_Tab1.Create(WS_CHILD|WS_VISIBLE,CRect(0,0,150,45),this,1);<br />
<br />
	TC_ITEM TabCtrlItem;<br />
TabCtrlItem.mask = TCIF_TEXT|TCIF_PARAM|TCIF_STATE;<br />
	TabCtrlItem.dwState=TCIS_HIGHLIGHTED ;<br />
<br />
	CStringArray m_GetString;<br />
	m_GetString.Add("Item1");<br />
	m_GetString.Add("Item2");<br />
	m_GetString.Add("Item3");<br />
	for(int i=0;i<m_GetString.GetCount();i++)<br />
	{<br />
	TabCtrlItem.pszText = CT2A(m_GetString.GetAt(i));<br />
		TabCtrlItem.lParam=i;<br />
	m_Tab1.InsertItem( i, &TabCtrlItem );<br />
	}<br />
<br />

WhiteSky

Andy Rama2-Aug-06 23:11

2-Aug-06 23:11

WhiteSky wrote:
for(int i=0;i {
TabCtrlItem.pszText = CT2A(m_GetString.GetAt(i));

error in these line. 'CT2A' : undeclared identifier

WhiteSky wrote:
m_Tab1.InsertItem( i, &TabCtrlItem );

InsertItem() will add tabs in Tab Control.... instead of that can I add dialogs ( other newly created dialogs) in Tab Control as a new tab?

Hamid_RT3-Aug-06 0:52

how to convert a word file to text file

3-Aug-06 0:52

if you use vs2005 you can LPTSTR() instead CT2A or see

<br />
	TCHAR lp[120];<br />
	lp[0]='\0';<br />
	strcat(lp,"test");<br />
TabCtrlItem.pszText = lp;//CT2A(m_GetString.GetAt(i));<br />

Aniket Salunkhe wrote:
can I add dialogs ( other newly created dialogs) in Tab Control as a new tab?

See CPropertyPage Class
[^]and see examples in this page

WhiteSky

georgekjolly1-Aug-06 4:38

georgekjolly

1-Aug-06 4:38

Hi All,

I need to convert a word file to text. How it can be possible in VC++,

Please Help me
Thanks in Advance
George K Jolly

Re: how to convert a word file to text file

toxcct1-Aug-06 4:39

Re: how to convert a word file to text file

1-Aug-06 4:39

you have to know the word format, which is proprietary format... so, good luck Cool | :cool:

TOXCCT >>> GEII power

[VisualCalc 3.0 updated ][Flags Beginner's Guide new! ]

David Crow1-Aug-06 4:51

David Crow

1-Aug-06 4:51

Using Word automation, open the file and save it as a text file.

"Money talks. When my money starts to talk, I get a bill to shut it up." - Frank

"Judge not by the eye but by the heart." - Native American Proverb

Get Current Logged on User

Programm3r1-Aug-06 4:33

Programm3r

1-Aug-06 4:33

Hi all,

Can someone plz point me to a site or give me some advice on getting the currently logged on user (windows system).

Thanx in advance.

Regards

Programm3r

Re: Get Current Logged on User

David Crow1-Aug-06 4:51

David Crow

1-Aug-06 4:51

Will GetUserName() work for you?

"Money talks. When my money starts to talk, I get a bill to shut it up." - Frank

"Judge not by the eye but by the heart." - Native American Proverb

Re: Get Current Logged on User

Programm3r1-Aug-06 5:07

Programm3r

1-Aug-06 5:07

Thanx .... already came right.
Smile | :)

Regards

Programm3r

CButton with BS_OWNDERDRAW

YaronNir1-Aug-06 4:17

YaronNir

1-Aug-06 4:17

I've derived a class from CButton, i draw the states. i use the BS_OWNDERDRAW style. i've read that i can't use both BS_PUSHBUTTON and BS_OWNDERDRAW.

problem starts that when i have a dialog contains this button, and i am on focus on a different dialog, pressing this button will only set the focus to the first dialog (the one that the button is on) and not operate the BN_CLICK message on the button. pressing on the button again will operate it....it is not a common behaviour of CButton...

how can i resolve that

thanks in advanced

Yaron

Interface basics click here :
http://www.codeproject.com/com/COMBasics.asp

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Re: CButton with BS_OWNDERDRAW

Hamid_RT1-Aug-06 4:48