C / C++ / MFC

Re: cscrollview snaps back to zero when you scroll past 32760 pixels

25-Aug-04 12:35

Hi there,

I have a CScrollView containing a large document. When I scroll horizontally and get to a horizontal scroll position of around 32760 pixels the scroll snaps back to the zero horizontal position. This only happens if I scroll by dragging the scrollbar itself. If I click on the little arrow at the end of the scrollbar there is no problem and it can scroll horizontally beyond 32760 pixels.

Does anybody know what could be causing this behaviour? My scrollview class does not override any of the basic scrolling functions so I feel confident it's not a bug that I've programmed in myself.

Thanks for your help!

mick

mickelliot25-Aug-04 12:41

Re: cscrollview snaps back to zero when you scroll past 32760 pixels

25-Aug-04 12:41

Hello again,

I just tested this by building a new mdi application in visual studio.net, using cscrollview as the base view class. The only change I made after the initial files were created by the ide was to set the horizontal scroll width to 35000 pixels in the view's "oninitialupdate" function. True enough, when you scroll towards the end of the view past around 32000 pixels, it hops straight back to zero!

I'd be really grateful if anybody could suggest a way of overcoming this limitation.

Regards,

Mick

Joaquín M López Muñoz25-Aug-04 13:03

Joaquín M López Muñoz

25-Aug-04 13:03

It's a legacy from the 16bit days (only applies to Win9x, not 2000/XP). Check this article[^]. Seems like you will have to create your own scroll view deriving directly from CView.

Joaquín M López Muñoz
Telefónica, Investigación y Desarrollo

Re: cscrollview snaps back to zero when you scroll past 32760 pixels

mickelliot29-Aug-04 8:44

29-Aug-04 8:44

Thanks for the answer Joaquín

Mick

solution to this problem

mickelliot31-Aug-04 11:08

Accessing a Class Variable Using A Void Pointer

31-Aug-04 11:08

Just in case anybody finds this post doing a google search or something, I found a solution to the problem at codeguru (http://www.codeguru.com/Cpp/W-D/doc_view/scrolling/comments.php/c3299/?thread=41682)

You just have to override onscroll as shown below:

BOOL <br />
CMyiew::OnScroll(UINT nScrollCode, UINT nPos, BOOL bDoScroll)<br />
{<br />
	if (GetTotalSize().cx >= SHRT_MAX || GetTotalSize().cy >= SHRT_MAX )<br />
	{	<br />
		SCROLLINFO info;<br />
		info.cbSize = sizeof(SCROLLINFO);<br />
		info.fMask = SIF_TRACKPOS;<br />
<br />
		//nPos is valid only is scroll code is SB_THUMBTRACK<br />
		if (LOBYTE(nScrollCode) == SB_THUMBTRACK)<br />
		{<br />
			GetScrollInfo(SB_HORZ, &info);<br />
			nPos = info.nTrackPos;<br />
		}<br />
		else if (HIBYTE(nScrollCode) == SB_THUMBTRACK)<br />
		{<br />
			GetScrollInfo(SB_VERT, &info);<br />
			nPos = info.nTrackPos;<br />
		}<br />
	}<br />
<br />
	BOOL ret = CScrollView::OnScroll(nScrollCode, nPos, bDoScroll);<br />
<br />
<br />
	return ret;<br />
}

Anonymous25-Aug-04 10:47

Re: Accessing a Class Variable Using A Void Pointer

25-Aug-04 10:47

Basically I want to loop through a link list that I have. It wouldnt be hard if in the link list their might be classes with different data types. So I am trying to use the void pointer. Because I dont know the data type of the class and I want to try and make a function that returns the address of the last class in the link list. I am able to use templates but everything works well until I try to get the void pointer in a class to equal the void pointer of the next class in the link list. I dont see why it doesnt work because I keep getting the error error C2227: left of '->NextObject' must point to class/struct/union. I am pointing to a class void pointer and Node is suppose to be a class so I dont understand why I am getting the error. I tried casting to fix this problem either I dont know how to do it well or it doesnt work to fix this.If anyone can help I would be extremly greatful.

#include <stdlib.h>
#include <windows.h>
#include <stdio.h>
#include <iostream>
#include <fstream>
#include <string>
#include <conio.h>
#include <windows.h>

class Room
{
public:
void *NextObject;
Room();
};

Room::Room()
{
NextObject = 0;
name = "blue";
}

using namespace std;
Room *RoomHead;

template <class X> X *FindEndObject(X * Node)
{
void *Temp = Node;
while (Temp!=0)
{
Temp = Temp->NextObject;
cout << "MOo" << endl;
}
return Node;
}

void main()
{
void *NewRoom = FindEndObject(RoomHead);
system("PAUSE");
}

Doug Mitchell25-Aug-04 11:21

Doug Mitchell

25-Aug-04 11:21

A void* doesn't have a NextObject method. You would need to cast this to the appropriate object with something like

Room* tmpRoom = reinterpret_cast<Room*>(Node)

tmpRoom will be null if the cast fails.

Re: Accessing a Class Variable Using A Void Pointer

Joaquín M López Muñoz25-Aug-04 12:40

Joaquín M López Muñoz

25-Aug-04 12:40

Room* tmpRoom = reinterpret_cast(Node)

Ummm... static_cast would suffice (and in general is preferrable to reinterpret_cast.)

tmpRoom will be null if the cast fails.

Oh, this behavior is only provided by dynamic_cast, and this type of cast can only be applied to convert from a virtual class to a virtual class, which is not the case. So, IMHO static_cast should be used, and the cast does not fail ever (of course, if Node didn't point to an actual Room object, then the program could crash or whatever.)

Joaquín M López Muñoz
Telefónica, Investigación y Desarrollo

Joaquín M López Muñoz
Telefónica, Investigación y Desarrollo

Re: Accessing a Class Variable Using A Void Pointer

Anonymous25-Aug-04 12:42

Re: Accessing a Class Variable Using A Void Pointer

25-Aug-04 12:42

I tried doing so and with a few changes I finally got the program to compile with this modify function

template <class x=""> void *FindEndObject(X *Node)
{
X* Temp1;
if(Node->Next==NULL)
{
return Node->Next;
}
void *Temp = Node->Next;
cout << "Hey Friend" << endl;
while (Temp!=NULL)
{
cout << "Hey Friend" << endl;
Temp1 = reinterpret_cast<x*>(Temp);
Temp = Temp1->Next;

}
return Temp;
}

But not the problem is that their is a runtime error at if(Node->Next==NULL) I dont understand why their would be a error if I am trying to see if Next == Null;

Joaquín M López Muñoz25-Aug-04 12:49

Joaquín M López Muñoz

25-Aug-04 12:49

But not the problem is that their is a runtime error at if(Node->Next==NULL) I dont understand why their would be a error if I am trying to see if Next == Null;

Maybe Node itself is null? Or maybe you're pasing an invalid pointer.

Joaquín M López Muñoz
Telefónica, Investigación y Desarrollo

Re: Accessing a Class Variable Using A Void Pointer

Anonymous25-Aug-04 14:12

Re: Accessing a Class Variable Using A Void Pointer

25-Aug-04 14:12

Sorry I didnt see the post before I posted my last message and I tried to fix my program using the advice. I am still receiving the same runtime problem which stops at while (tmpRoom->Next!=0) Node shouldn't be NULL because Node would be a pointer to Room *RoomHead. Which is a global object. RoomHead->Next should = 0 because in the room constructure Next = 0; So FindEndObject should just return the value of tmpRoom because their is only one object in the link list. I tried every way to use the static_cast and I still cant get it to work. I am not even sure if I am doing it 100% correct. I dont want anyone to give me the code for the function because I will like to learn exactly how to do it my self. But if anyone could give me a little more detail hints I would appreciate it alot because right now I am not 100% sure how to implement the advice I am getting to my code. I guess because of the fact I never used void pointer or used any form of cast.
This is how my program looks so far

#include <stdlib.h>
#include <iostream>

class Room
{
public:
void *Next;
Room();
};

Room::Room()
{
Next = 0;
}

using namespace std;
Room *RoomHead;

template <class X> X *FindEndObject(X * Node)
{
X* tmpRoom = Node;

while (tmpRoom->Next!=0)
{
cout << "We Got Here" << endl;
tmpRoom = static_cast<X*>(tmpRoom->Next);

}
return Node;
}

void main()
{
void *NewRoom = FindEndObject(RoomHead);
system("PAUSE");
}

DRHuff25-Aug-04 17:14

Re: Accessing a Class Variable Using A Void Pointer

25-Aug-04 17:14

RoomHead is a pointer not an object. As such it has never called the constructor.

Declare it as

Room RoomHead

instead.

Dave

Anonymous25-Aug-04 18:11

dumb command line question

25-Aug-04 18:11

Lol thank you alot. I can't believe I didn't notice that. Thanks to everyone who helped me with my program.

Butting in...

palbano25-Aug-04 18:06

palbano

25-Aug-04 18:06

You should question any design that entails objects being cast from void*. In general it's just plain bad.

But, that's just my opinion... I could be wrong.

-pete

kfaday25-Aug-04 9:55

kfaday

25-Aug-04 9:55

Hi, i've got the following line in my app:

printf("Press Enter to continue\n");
...
clrscr();

i want to display the message until the user presses enter and then clear the screen.
what command should i use for that?
I need only ANSI C commands
i remember that in pascal you can use
readln;

thanks!

Re: dumb command line question

David Crow25-Aug-04 10:10

David Crow

25-Aug-04 10:10

How about:

do
{
    printf(...);
} while (getch() != 0xa);  // or 0xd
clrscr();

"When I was born I was so surprised that I didn't talk for a year and a half." - Gracie Allen

Re: dumb command line question

DRHuff25-Aug-04 10:13

Bolding dates in CDateTimeCtrl

25-Aug-04 10:13

#include <conio.h>

getch();

getch will wait until any key is pressed - test the return for
'\n' if you want the enter key.

do
{
ret = getch()
}
while (ret != '\n');

Dave

DRHuff25-Aug-04 9:42

Re: Bolding dates in CDateTimeCtrl

25-Aug-04 9:42

I cannot get specific dates to go bold in the DateTimeCtrl. I want to specify which days are bolded in the popup calendar. I do the following:

OnDropdownDateTimePicker(...)
{
CMonthCalCtrl * cal = m_ctrlDTP.GetMonthCalCtrl();
MONTHDAYSTATE *md;
short len;
SYSTEMTIME tFrom, tTo;

if (cal)
{
cal->ModifyStyle(0, MCS_DAYSTATE); // change style to allow daystates
len = cal->GetMonthRange(&tFrom, &tTo, GMR_DAYSTATE);
md = new MONTHDAYSTATE [len];
memset(md, 0, sizeof(MONTHDAYSTATE) * len);

BOLDDAY(ms[0], 1); // MS macro to set day 1 of first month bold

cal->SetDayState(len, ms);
}

}

and nothing happens. Mad | :mad:

Anybody know what I am missing? Confused | :confused:

Thanks

Dave

David Crow25-Aug-04 10:17

David Crow

25-Aug-04 10:17

DRHuff wrote:
Anybody know what I am missing?

Per MSDN:

After creating the control, you can change all of the styles except for MCS_DAYSTATE and MCS_MULTISELECT. To change these styles, you will need to destroy the existing control and create a new one that has the desired styles.

"When I was born I was so surprised that I didn't talk for a year and a half." - Gracie Allen

Re: Bolding dates in CDateTimeCtrl

DRHuff25-Aug-04 10:38