C / C++ / MFC

Richard MacCutchan2-Nov-13 21:27

2-Nov-13 21:27

You are correct about how it works, see http://msdn.microsoft.com/en-us/library/windows/desktop/ms644927(v=vs.85).aspx#handling[^]. As to your problem, I think you need to provide some more detail.

Veni, vidi, abiit domum

pasztorpisti3-Nov-13 5:25

pasztorpisti

3-Nov-13 5:25

A bit of correction: Each thread has a message queue and each window belongs to the thread that created it. When you send a message to a window then the message is (automatically) put into the message queue of the thread that owns the window. The message will be passed to the window by the owner thread when it decides to get a message from its message queue and decides to dispatch it (EDIT: a bit of correction here: sent messages and some other messages are handled specially (like WM_QUIT/WM_PAINT) and/or out of order of the queue). A child control sends most of its commands/notifications (not window messages!!!) to its parent window and these are automatically put into the owner thread of the parent window (the child window has nothing to do with the owner thread of the parent window and the message queue of the owner thread, that is handled by the system automatically). Only a few specific "messages" (commands/notifications) are passed to the parent window, the rest (most) of the messages are processed by the window proc that belongs the the class of the child control. The "notifications" and "commands" that are passed to the parent usually arrive as WM_COMMAND and WM_NOTIFY messages to the window proc of the parent window. (There are a few exceptions, like WM_CTLCOLOR...)

modified 3-Nov-13 13:06pm.

lrinish3-Nov-13 6:32

lrinish

3-Nov-13 6:32

Not confusing at all! I think things are getting clearer. This is my main initial confusion.

Window Procedure

A window procedure is a function that receives and processes all messages sent to the window. Every window class has a window procedure, and every window created with that class uses that same window procedure to respond to messages.

The system sends a message to a window procedure by passing the message data as arguments to the procedure. The window procedure then performs an appropriate action for the message; it checks the message identifier and, while processing the message, uses the information specified by the message parameters.

I think the key confusion for me is what Windows considered a "CLASS".

pasztorpisti, thanks again but can you clarify something for me? When you say "(not window messages!!!)" your not talking about "WM_*" messages but messages that are specific to a class like "BM_*", "LB_*", "CB_*", and ...?

Arithmetic operation in pointer using C

pasztorpisti3-Nov-13 7:01

pasztorpisti

3-Nov-13 7:01

You are right. Classic window messages (like WM_PAINT, WM_SIZE, ...) are all processed by the window proc of the control itself (that is window class specific). Specialized child windows (controls like Button, Edit, ...) are designed that they send only a few messages to the parent window (like WM_COMMAND message when the user presses a button, and WM_NOTIFY with control specific struct pointer).

I guess this design was created because back in the old days people wrote their programs in procedural languages (C, Pascal) and in that case it is more comfortable to write just one windowproc for your window and to handle all child control messages there instead of writing a lot of window procs for all buttons, edit boxes, and so on... If you think about it, most of the core windows API is also a C interface.

The irony here is that today GUIs are mostly built with object oriented GUI frameworks where one control is one object (I'm not talking about MFC here, that is at most 1/3 object oriented, Qt is a much better example). Such a framework needs to have/handle all control specific messages/notifications in the object associated with the control. For this reason the window specific implementation of such a framework usually delegates the handling of child control speicific messages from the parent object to the child object. Later the programmer usually registers an event handler into the object of the child control. You also need all control specific messages in the object associated with the child control when you want to write reusable specializations of some windows-builtin child controls (like static or edit).

shanmugarajaa31-Oct-13 20:20

shanmugarajaa

31-Oct-13 20:20

Hi friends,
I tried out something like this which is given below in VC++ by referring Dennis M. Ritchie (ANSI C second edition) book examples.

struct Key *low = &tab[0];
struct Key *high = &tab[n];
struct Key *mid;

mid = low + (high-low) / 2; // Error: cannot convert from 'int' to 'struct Key *'

My question is how they are using this expression mid = low + (high-low) / 2;?. I don't know whether I misunderstood the concept or there is some difference between ANSI C and VC++. Please anyone help me in this.

Regards,
S.Shanmuga Raja

Re: Arithmetic operation in pointer using C

Richard MacCutchan31-Oct-13 23:47

Re: Arithmetic operation in pointer using C

31-Oct-13 23:47

Which compiler gives the error? I just tried this with Visual Studio 2010 C++ compiler and it compiles correctly, as it should, in both .c and .cpp versions.

Veni, vidi, abiit domum

Bill_Hallahan1-Nov-13 18:22

Bill_Hallahan

1-Nov-13 18:22

There is a difference between ANSI C, some other C++ compilers, and what Visual Studio allows for pointer arithmetic.

Pointer arithmetic is not allowed on all platforms, as least not allowed the way you have it. There is a ptrdiff_t macro that allows taking pointer differences on many platforms, but I'm not sure whether that is allowed in ANSI C or not. In any event, that is not what you need.

Some compilers will let you cast a pointer to be type size_t, however, that is not portable across all platforms and compilers and is generally not a good practice.

Presumably, the array tab is defined to be an array of Key structures:

So, to write portable code, write code something like this:

C++

int BinarySearch(int low, int high, struct Key x)
{
    int index = -1;
    int mid = 0;

    while (low <= high)
    {
        mid = (low + high) >> 1;

        if (firstKeyLessThanSecondKey(x, tab[mid]))
        {
            high = mid - 1;
        }
        else if (firstKeyLessThanSecondKey(tab[mid], x))
        {
            low = mid + 1;
        }
        else
        {
            index = mid;
        }
    }

    return index;
}

To search the entire tab array for a Key equal to x, pass 0 for low and the array length minus 1 for high.

This will return -1 if the Key that matches x is not found, otherwise the index into the array tab for the key that matches x will be returned.

Because the values of low and high are always positive, a shift can be used for the divide by 2.

C++

mid = (low + high) >> 1;

Of course, you'll have to modify this code for your application. I made some assumptions based on the book you cited.

Also, if the Key structure isn't very small, then instead of passing the Key structure by value, you might want to pass a pointer to a Key to both the BinarySearch function and to the FirstKeyLessThanSecondKey function.

Finally, I didn't compile and test this. I'm never 100% sure if code is correct until I debug it under varied conditions. If not correct, I expect this is very close to correct.

modified 2-Nov-13 0:51am.

ListView::LVN_EndLabelEdit problem

jackheroes31-Oct-13 8:51

jackheroes

31-Oct-13 8:51

The MSDN says if you you return TRUE from LVN_EndLabelEdit notification, the control will accept the new edited text.

It's not true for my experiments.
I tried return TRUE, it didn't work, the label stays unchanged.

...
BOOL OnEndLabelEidt( ..., LPNMLVDISPINFO pDispInfo)
{
return TRUE ; // doesn't work

// so I have to do it manually
LVITEM item ;
...
item.pszText = pDisInfo->item.pszText ;
ListView_SetItem(hListview, &item ) ; // then it works
}

As it isn't TRUE for any other notfications.
such as TreeView::TVN_EndEditLabel.

TreeView::TVN_EXPANDING returns TRUE expands the node anyway, which conflicts with the Documentation either.

Could someone give me a clue? Thanks.

Re: ListView::LVN_EndLabelEdit problem

Richard MacCutchan31-Oct-13 15:09

Re: ListView::LVN_EndLabelEdit problem

31-Oct-13 15:09

If you think the documentation is wrong then you should report it to Microsoft.

Veni, vidi, abiit domum

jackheroes31-Oct-13 19:52

jackheroes

31-Oct-13 19:52

I am confused. I think there must be something wrong in my comprehension,

Re: ListView::LVN_EndLabelEdit problem

Richard MacCutchan31-Oct-13 23:37

31-Oct-13 23:37

See http://msdn.microsoft.com/en-us/library/windows/desktop/bb774814(v=vs.85).aspx[^], for details of how this is supposed to work.

Veni, vidi, abiit domum

test

Member 1036994131-Oct-13 5:37

Member 10369941

31-Oct-13 5:37

<pre lang="cs">void Test::OnDrawSortArrow(CDC* pDC, CRect rectArrow)
{
Metafile * emf = NULL;

emf = LoadMetafile(IDR_ICON_EXPAND, NULL, true);
Gdiplus::Bitmap* image = BitmapFromEmf(emf, 8, 8, Color(255,82,82,82), 0);

HICON hIcon = NULL;

if(IsAscending())
image->RotateFlip(Rotate180FlipNone);

image->GetHICON(&hIcon);

pDC->DrawIcon(rectArrow.TopLeft().x - 20, rectArrow.TopLeft().y - 10, hIcon);

delete emf;
}</pre>

Re: test

jeron131-Oct-13 6:01

jeron1

31-Oct-13 6:01

return value

messages28-Oct-13 4:20

messages

28-Oct-13 4:20

This recursive function doesnt have a end point,becuase 12 item is not exist in the array.How we can fix this recursive function to solve this problem?

C++

int _tmain(int argc, _TCHAR* argv[])
{
     int arr[10] = {1,2,3,4,5,6,7,8,9,10};
    int sum;

	  sum=BinSearch(arr,12,0,9);
		  cout<<sum;

	return 0;

}

int BinSearch(int A[],int item,int low,int height)
{
		int mid;
		mid=(low+height)/2;
		if(A[mid]==item)
			return mid;
		else if(item > A[mid])
			return Binary_Search(A,item,mid+1,height);
		else
			return Binary_Search(A,item,low,mid-1);
}

Joe79428-Oct-13 5:00

Joe794

28-Oct-13 5:00

Add as 1st line in BinSearch:

if(low > height)return -1; // Return 'not found' code

messages28-Oct-13 5:33

messages

28-Oct-13 5:33

Thank you Joe794.

Aescleal28-Oct-13 6:11

Aescleal

28-Oct-13 6:11

The array passed into the function could potentially have any value in it you can't select a simple return value to represent your error condition. I'd consider throwing an exception rather than using a return value:

C++

if( A[low] > item || A[high] < item] ) throw binary_search_out_of_bounds();

Another option is to have the function return a std::pair<bool, int> where the first item in the pair tells the caller if they have an error condition or not and the second is the value they're after. Personally I find that a bit ugly and it complicates your code more as you have to do more in the calling function so I'd go with an exception.

Cheers,

Ash