C / C++ / MFC

C^hris L^osinger24-Feb-03 9:45

C^hris L^osinger

24-Feb-03 9:45

you can override new and delete for those objects and have them allocate from the global heap (via GlobalAlloc). that lets you keep your code looking like it does above. otherwise, as you've discovered, you can't share pointers allocated inside a DLL with the client application.

-c

When history comes, it always takes you by surprise.

Bobber!

Dave_24-Feb-03 10:04

Dave_

24-Feb-03 10:04

Thank you for the reply.

This will be a stupid question:

I am familiar with how to override new/delete for classes, but not for struct's. Can this be done, or do I have to change my struct to a class?

Thanks again.

C^hris L^osinger24-Feb-03 10:10

C^hris L^osinger

24-Feb-03 10:10

if these are C-style structs (typedef struct {....}), you could just allocate all the structs as one chunk of memory: GlobalAlloc(GPTR, sizeof(DSTRUCT) * numStructs). it's just like you would do with malloc.

if they are C++ structs (which are pretty much just classes with everything public by default), you can just override new/delete for that class (or struct).

-c

When history comes, it always takes you by surprise.

Bobber!

Alvaro Mendez24-Feb-03 10:47

Error returning CStringArray as function result?

24-Feb-03 10:47

There are two problems here:

1. You're trying to delete the elements of the array individually. You allocate the array as one block of 15 elements and then you try to delete each element one at a time. That's not going to work. You must free the entire array in one shot:

delete [] pData;

2. Allocating on the DLL and then freeing on the app is generally a bad idea. If the memory is not allocated/freed the same way across both modules, it will cause a crash. So it's best to stick with the policy of making the one who creates the memory be the one who frees it.

Add a mydllFreeData member:

void mydllFreeData(DSTRUCT* pds)
{
   delete [] pds;
}

Regards,
Alvaro

The world is a dangerous place, not because of those who do evil, but because of those who look on and do nothing. -- Albert Einstein

yasbas24-Feb-03 9:29

yasbas

24-Feb-03 9:29

Hi,

I have a function like this:

CStringArray CSearch::SearchNode(CString csDesiPin)
{
CStringArray a;
a.Add("test");
return a;
}

But when I try to compile there is an error:

error C2558: class 'CStringArray' : no copy constructor available

Why is that, what is wrong?
Thanks in advance!

Re: Error returning CStringArray as function result?

Dave_24-Feb-03 9:33

Dave_

24-Feb-03 9:33

Since you are not passing a pointer, a copy of the CStringArray is needed. If you derive a class from CStringArray, you can create a copy constructor to do this. An easier method would be to pass a pointer to a CStringArray, and not create a second CStringArray within the function.

Re: Error returning CStringArray as function result?

Christian Graus24-Feb-03 9:52

Christian Graus

24-Feb-03 9:52

I find it's better to pass in an object like this by reference as a parameter instead of returning a pointer. I usually return an error code instead.

As a rule, the standard collection of containers is a far better choice than the tinker toys that ship with MFC.

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

It'd probably be fairly easy to make a bot that'd post random stupid VB questions, and nobody would probably ever notice - benjymous - 21-Jan-2003

Re: Error returning CStringArray as function result?

Alvaro Mendez24-Feb-03 10:27

Re: Error returning CStringArray as function result?

24-Feb-03 10:27

Christian Graus wrote:
As a rule, the standard collection of containers is a far better choice than the tinker toys that ship with MFC.

You never miss a chance, do you? Smile | :)

Regards,
Alvaro

The world is a dangerous place, not because of those who do evil, but because of those who look on and do nothing. -- Albert Einstein

Christian Graus24-Feb-03 10:29

Christian Graus

24-Feb-03 10:29

Alvaro Mendez wrote:
You never miss a chance, do you?

Not if I can help it, no. I've been too quiet on this forum for some time, and *someone* needs to make a stand for righteousness....

Christian

NO MATTER HOW MUCH BIG IS THE WORD SIZE ,THE DATA MUCT BE TRANSPORTED INTO THE CPU. - Vinod Sharma

Re: Error returning CStringArray as function result?

Alvaro Mendez24-Feb-03 11:03

Re: Error returning CStringArray as function result?

24-Feb-03 11:03

Preach it brother! Halleluya! Smile | :)

By the way, I went to a Christian church for the first time a couple of weeks ago and saw the preacher "healing" a bunch of cancer-ridden people. As he was chanting over each one of them, I noticed that several of them were fainting and falling backwards, just like on TV! OMG | :OMG:

What is your explanation for this behavior?

Also, I was only there for about 30 minutes -- got there late -- and I swear I must have counted about 30 Halleluyas coming from the preacher. Overall, it was an interesting experience.

Regards,
Alvaro

The world is a dangerous place, not because of those who do evil, but because of those who look on and do nothing. -- Albert Einstein

Christian Graus24-Feb-03 11:31

Christian Graus

24-Feb-03 11:31

Alvaro Mendez wrote:
saw the preacher "healing" a bunch of cancer-ridden people.

Hmmm... According to the Bible, anyone can pray to God and expect to be healed. I know several people healed of cancer, including one who was prayed for when not a Christian and was converted as a result of being healed by God.

Alvaro Mendez wrote:
As he was chanting over each one of them, I noticed that several of them were fainting and falling backwards, just like on TV!

Urg.

Alvaro Mendez wrote:
What is your explanation for this behavior?

Groupthink ? Basically people fall over because they know it's expected of them/encouraged. The Bible has nothing to say about people falling over, it's part of the circus many 'modern' churches engage in. In fact, they call it being 'slain in the Spirit', the closest the Bible comes to referring to this is when God *KILLED* people in the Old Testament who opposed Him. The 'slain of the Spirit' in the Bible were dead, dead, dead.

Christian

NO MATTER HOW MUCH BIG IS THE WORD SIZE ,THE DATA MUCT BE TRANSPORTED INTO THE CPU. - Vinod Sharma

deleting a CDialog...

ns24-Feb-03 9:03

24-Feb-03 9:03

I spawn a modeless CDialog derived object from my MDI view class. When the user closes this CDailog with the system menu, I want to get rid of it totally.....

I did a new to create it in the View. If I put a delete this in the destructor of the cdialog is that enough? Also I created this object locally. Is there a problem with that and doing the delete? (if indeed the delete is legal..?)

Appreciate your help,
ns

Alvaro Mendez24-Feb-03 9:15

24-Feb-03 9:15

Some points:

1. Putting "delete this" in the destructor will not work. If the destructor is being called it's because the object is already being destroyed. So if you try to destroy it again... Dead | X|

2. The proper way to get rid of modeless dialog boxes is with DestroyWindow. Call that inside your OnCancel or OnOK functions. Alternately, you can do a "delete this" instead, which will call DestroyWindow. However, "delete this" will blow up if the dialog box is not created with new every time, so be careful.

3. If the dialog is modeless, the user will be able to create more than one of it. If that's not OK with you, how do you prevent it?

Regards,
Alvaro

The world is a dangerous place, not because of those who do evil, but because of those who look on and do nothing. -- Albert Einstein

ns24-Feb-03 9:22

24-Feb-03 9:22

urgh.....only one Cdialog to be created....I havent thought of it yet...maybe set some sort of flag?

I dont have an onOK or onCancel.....I just want the dlg dismissed with the system menu. So thats why I thought if I did delete this in OnClose() it might work? I didnt state this yet so what do you think about this idea?

you said" it will blow up..." why ?

Appreciate your help,
ns

Alvaro Mendez24-Feb-03 10:22

oay, got it! Quick ques..

24-Feb-03 10:22

Here's what I would do:

1. Use this code to create the dialog box:

static CMyDlg s_dlg;
 
if (!::IsWindow(s_dlg.m_hWnd))
   s_dlg.Create(CMyDlg::IDD, this);
s_dlg.ShowWindow(SW_SHOWNORMAL);

2. Inside your OnClose, call DestroyWindow();

This ensures your dialog is created only once and that it's properly destroyed.

ns wrote:
you said" it will blow up..." why ?

Sorry, typo. I modified my post. I meant that it will blow up if you call delete this and the dialog is not created with new. It's because it will try to free memory from the heap which wasn't allocated on the heap to begin with.

Regards,
Alvaro

The world is a dangerous place, not because of those who do evil, but because of those who look on and do nothing. -- Albert Einstein

ns25-Feb-03 2:14

25-Feb-03 2:14

Many thanks!

Quick question:

I've got three (actually decided at run time) buttons on my project and each will spawn a CDialog. If I use the same variable s_dlg is it okay? (No static right? )THe only things i will do with these CDlgs is a. close them, or b.resize them. So in the OnClose, with your strategy, will the code know which window to destroy? SInce now s_dlg is only pointing to the last CDlg created....

Appreciate your help,
ns

Re: oay, got it! Quick ques..

Alvaro Mendez25-Feb-03 4:25

25-Feb-03 4:25

Well, if it's 3 separate dialog boxes, I recommend you create 3 separate methods, each with its own static object:

void CMyView::OnButton1()
{
   static CMyDlg s_dlg;
   s_dlg.Create(this);
}
 
void CMyView::OnButton2()
{
   static CMyDlg s_dlg;
   s_dlg.Create(this);
}
 
void CMyView::OnButton3()
{
   static CMyDlg s_dlg;
   s_dlg.Create(this);
}

Then you can add this method to your dialog class:

void CMyDlg::Create(CWnd* pParentWnd)
{
  if (!::IsWindow(m_hWnd))   
    CDialog::Create(IDD, pParentWnd);
  ShowWindow(SW_SHOWNORMAL);
}

Regards,
Alvaro

The world is a dangerous place, not because of those who do evil, but because of those who look on and do nothing. -- Albert Einstein

thanks!! Also need to know...

Nish Nishant24-Feb-03 9:17

Nish Nishant

24-Feb-03 9:17

See this article :-

http://www.codeproject.com/dialog/gettingmodeless.asp[^]

There is a sub-section titled "Destroying the modeless dialog"

Regards,
Nish

Author of the romantic comedy

Summer Love and Some more Cricket [New Win]

Review by Shog⁹
Click here for review[NW]

ns24-Feb-03 9:28

24-Feb-03 9:28

Great article! Also need to know ....this CDialog is merely informational. So I dont refresh it (may resize it), so is it better to use a local variable or a member variable? I can easily push the pointers onto a vector, so thats not a problem....I just dont knoew if its necessary> Can I use the info in the article in the event that I create a local variable each time the button is pressed to spawn a new dlg?

Appreciate your help,
ns

what I have are a set of cdlgs which in turn send messagse to the view when their button is pressed, wehich spawns the other CDlg. SO yes I can have many CDlgs - thats okay, but only one for each original CDlg which sent the message (the one with buttons)

valikac24-Feb-03 9:17

valikac

24-Feb-03 9:17

One solution is to declare a pointer to the dialog box as one of view's private members.

Inside OnClose(), call DestroyWindow(). Inside PostNcDestroy(), call
CDialog::PostNcDestroy() and delete the object via "delete this." Post a message to the view class and set the pointer to NULL.

Kuphryn