C / C++ / MFC

safe to delete immediately following CWnd::DestroyWindow?

24-Oct-07 13:41

I'd say this is too much information.

It's hard to tell how to help.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~<br />
Peter Weyzen<br />
Staff Engineer<br />
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Peter Weyzen23-Oct-07 19:22

Re: safe to delete immediately following CWnd::DestroyWindow?

23-Oct-07 19:22

Am doing a little code review...

Is it safe to delete a CWnd derived object immediately following a call to CWnd::DestroyWindow on it?

I would assume yet -- but if not, when is it safe to do so?

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~<br />
Peter Weyzen<br />
Staff Engineer<br />
<A HREF="http://www.soonr.com">SoonR Inc -- PC Power delivered to your phone</A>

Nishad S23-Oct-07 20:17

Re: safe to delete immediately following CWnd::DestroyWindow?

23-Oct-07 20:17

See CWnd::PostNcDestroy()

- NS -

Naveen23-Oct-07 23:20

Naveen

23-Oct-07 23:20

May be NS17 meant you to read

TN017: Destroying Window Objects[^]

nave

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Re: safe to delete immediately following CWnd::DestroyWindow?

Nishad S24-Oct-07 0:00

Re: safe to delete immediately following CWnd::DestroyWindow?

24-Oct-07 0:00

Actually I meant the same that CFrameWnd do.

void CFrameWnd::PostNcDestroy()
{
	// default for frame windows is to allocate them on the heap
	//  the default post-cleanup is to 'delete this'.
	// never explicitly call 'delete' on a CFrameWnd, use DestroyWindow instead
	delete this;
}

- NS -

Naveen24-Oct-07 0:17

Naveen

24-Oct-07 0:17

But you told him to check the CWnd::PostNcDestroy() Confused | :confused:

nave

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Re: safe to delete immediately following CWnd::DestroyWindow?

Nishad S24-Oct-07 0:20

Re: safe to delete immediately following CWnd::DestroyWindow?

24-Oct-07 0:20

Ofcourse. MSDN clearly says "Derived classes can use this function for custom cleanup such as the deletion of the this pointer." in Remarks section. Please have a look.

- NS -

Naveen24-Oct-07 0:27

Naveen

24-Oct-07 0:27

Thats ok. After checking that function in MSDN, he will understand that he can delete this pointer from the postncdestroy() function. But his question was whether its safe to delete a CWnd pointer and the above explanation doesnt answer it. Like if it is not safe, why?

nave

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Re: safe to delete immediately following CWnd::DestroyWindow?

Nishad S24-Oct-07 0:35

Re: safe to delete immediately following CWnd::DestroyWindow?

24-Oct-07 0:35

His question is a little bit different. He asked whether it can be done from DestroyWindow. But PostNCDestroy is called from void CWnd::OnNcDestroy() which is called when WM_NCDESTROY is sent to that window. WM_NCDESTROY is the last message received by the window in destruction. So I think it is safe to use, if it is safely handled. I mentioned that CFrameWnd is using this technique safely.

- NS -

Peter Weyzen24-Oct-07 13:42

question on operator * and &

24-Oct-07 13:42

One thing I find inside the Destroy -- is a call to Detach -- which seperates the HWND from the CWnd. It seems safe to delete at that time.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~<br />
Peter Weyzen<br />
Staff Engineer<br />
<A HREF="http://www.soonr.com">SoonR Inc -- PC Power delivered to your phone</A>

King Tran23-Oct-07 19:01

King Tran

23-Oct-07 19:01

assumption:
char c[4]={1,2,3,4};
char* addr=c;
then addr is the address of c[0], the address c is the address c[0];then i want to know, what is the mean and value of &c? what is the mean of (int*)&c ?

thanks

Neo Andreson23-Oct-07 19:06

Neo Andreson

23-Oct-07 19:06

It is pointer to pointer i.e. int**

Nishad S23-Oct-07 20:30

23-Oct-07 20:30

Lao Wang wrote:
what is the mean and value of &c?

It is the address of c array. It will be same as &c[0].

Lao Wang wrote:
what is the mean of (int*)&c ?

It is only a conversion of pointer from (char*) to (int*)

- NS -

toxcct24-Oct-07 1:33

toxcct

24-Oct-07 1:33

NS17 wrote:
It is only a conversion of pointer from (char*) to (int*)

char* ? or char** ?

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Nishad S24-Oct-07 1:49

24-Oct-07 1:49

Yes char** is correct.

I mentioned only about the memory adresss.

- NS -

toxcct24-Oct-07 0:29

toxcct

24-Oct-07 0:29

you already got some good answers, but i'll sum it up.

c is defined as an array of char, so, basically, it can be seen as a char*.
& used as an unary operator means to return the address of the variable attached, so &c is the address of c.

but as c is a char*, its address is a char**.
in front of it, you have a cast operator, which casts the address returned into an int* address

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King Tran24-Oct-07 2:03

King Tran

24-Oct-07 2:03

thanks
as your mean, &c=char** , but the equation char ** c=&c, has compile wrong message with "can not convert from char (*）[4] to char **"
so i think &c != &c[0];

Run time error on my SQL database

toxcct24-Oct-07 2:06

toxcct

24-Oct-07 2:06

Lao Wang wrote:
so i think &c != &c[0];

how do you test this ?

BTW, c == &(c[0])
but the first element of the array is at the address of the beginning of the array

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CodingLover23-Oct-07 18:21

CodingLover

23-Oct-07 18:21

Hi all,

I create a database on SQL 2005 Express edition and link it to a C++/MFC application as follows. It wont gives any compile time errors. But at run time, it gives an error. Here are details.

Link the database in OnInitDialog()

here is the code

<br />
BOOL CSRFDBDlg::OnInitDialog()<br />
{<br />
        CDatabase srfDB ;<br />
        CString srfNAME ;<br />
<br />
	srfNAME = "ODBC; DSN=.SQLEXPRESS; UID=sa; PWD=sa123; DATABASE=srfdb.mdf" ;<br />
	srfDB.Open(srfNAME) ;<br />
	if(srfDB.IsOpen())<br />
	{<br />
		AfxMessageBox("ok") ;<br />
	}<br />
<br />
	srfDB.Close() ;<br />
}<br />

Gives the following runtime error
Data source name not found and no default driver specified

Can you guys tell me where I'm going wrong.... Frown | :(

I appreciate your help all the time...
Eranga Smile | :)

chandu00423-Oct-07 21:53

chandu004

23-Oct-07 21:53

have you defined the DSN in control panel>administrative settings>odbc..?
hope you have not.
gud luck.

---------------------------------------------

Suggestion to the members:
prefix your main thread subject with [SOLVED] if it is solved.
chandu.

CodingLover24-Oct-07 0:34

CodingLover

24-Oct-07 0:34

Hey, I've done it correctly Poke tongue | ;-P

I found a nice book there in the library, and according to that book I think it is easy to use SQLOLEDB.1, simply OLEDB connection.

What you think of it. Actually I'm on the right way now. Open the SQL database and write some values to it. Laugh | :laugh:

I appreciate your help all the time...
Eranga Smile | :)

chandu00424-Oct-07 0:41

chandu004

24-Oct-07 0:41

nice that you got your problem solved.
i have practically not used sql with vc++.
so i cannot suggest you any thing in that area.
gud luck.

--------------------------------------------
Suggestion to the members:
Please prefix your main thread subject with [SOLVED] if it is solved.
thanks.
chandu.

How to open files with spaces? (Beginner)

CodingLover24-Oct-07 1:26

CodingLover

24-Oct-07 1:26

Thank you. Let see what can I do for it.....

I appreciate your help all the time...
Eranga Smile | :)

VistaXP23-Oct-07 18:20

VistaXP

23-Oct-07 18:20

How do I open a file with spaces (ex. read me.txt). I know this can be done using getline(Input_File, File_Name), I've tried doing that, but with no luck.

Here's my function:

<br />
void TextInfo(void)<br />
{<br />
	ifstream Input_File;<br />
	string File_Name;<br />
	do<br />
	{<br />
		Input_File.open( GetString( "Enter name of file to read: " ).c_str() );<br />
		if ( Input_File )<br />
		break;<br />
		cout << "Bad file name, try again." << endl;<br />
		Input_File.clear();<br />
	} while ( true );<br />
<br />
	HoldScreen();<br />
}

Re: How to open files with spaces? (Beginner)

Peter Weyzen23-Oct-07 19:29