C / C++ / MFC

7-Jan-09 4:10

Hi,

I need to display ~ 100000 entries in a windows list which are stored in an SQL database (queried by a SELECT query with a few JOINs).

1st question: In only need to display a simple list. I would really like to use a Listbox Control for the sake of simplicity. Do I really need to choose a (complex) List Control?

2nd question: I tried a virtual list with a simple SQL query:

OnInitDialog()
...
// SELECT COUNT(*) FROM...
m_ctrlWords.SetItemCountEx(count);
....


OnLvnGetdispinfoWords(...)
...
sql.Format("SELECT keywordID, keyword FROM keywords ORDER BY keyword LIMIT %d, 1", index);
// query
const char *res = query.getStringField("keyword");
lstrcpy(pItem->pszText, res);

but this is really too slow.

I think I need OnLvnOdcachehintWords but it's somehow complicated. I could not find any concepts (which data structure to choose??) or examples concerning this Frown | :-(

The problem is that I have to remove old entried in cache (or my app's memory consumption would explode).

Does anyone have implemented such a virtual list (with data in SQL) already?

Are there some examples or concepts available?

Thank you very much,
Niki

Stuart Dootson7-Jan-09 4:34

7-Jan-09 4:34

You'll probably be better off executing something like "SELECT keywordID, keyword FROM keywords ORDER BY keyword" within OnInitDialog and caching the results in a resultset or whatever equivalent your database interface technology offers. Then you can interrogate the cache within OnLvnGetdispinfoWords and don't need to bother with OnLvnOdcachehintWords.

nobaq7-Jan-09 5:35

7-Jan-09 5:35

Hello,

I have to correct: The entries are much more than 100000...it's a fulltext recherche of a huge database system.

So it's definitifely too large to just read out all entries and cache them.

Regards,
Niki

nobaq7-Jan-09 6:04

7-Jan-09 6:04

I have tried it using caching and virtual list controls. Even if I read only the elements from LVN_ODCACHEHINT and cache them into a map, the list is really, really tooo slow.

What could be the solution? I just want to have the same as WinHelp32's keyword (or topic) search. For some reason, this list is very very fast since over 10 years (with slow computers).

Regards,
Niki

Stuart Dootson7-Jan-09 8:44

7-Jan-09 8:44

nobaq wrote:
I have tried it using caching and virtual list controls. Even if I read only the elements from LVN_ODCACHEHINT and cache them into a map, the list is really, really tooo slow.

I'm surprised - I've implemented virtual lists that provide views over 10s of thousands of rows (and 10s of columns) of data - they've been as quick as you could want.

I feel sure you're using the right technology (virtual list controls) but there's something not quite right about your implementation?

Stuart Dootson7-Jan-09 8:49

7-Jan-09 8:49

One other thing - have you profiled the code to see what is slowing it down?

I'd suggest implementing a virtual list control that just displays the numeric index of the list rows, to convince yourself that you've got the virtual list control set up correctly. Then work out how much of the SQL query you can do without taking too much time, and you can try to merge that into the list control implementation?

Stuart Dootson7-Jan-09 8:40

7-Jan-09 8:40

OK - in that case, you want to cache maybe a couple of hundred rows starting at the row that's at the top of the list control. Then, as users move down the list, you can retrieve a few hundred rows at intervals, when required?

David Crow7-Jan-09 5:33

David Crow

7-Jan-09 5:33

nobaq wrote:
I need to display ~ 100000 entries in a windows list...

Why? Who would want to navigate through such a list?

"Love people and use things, not love things and use people." - Unknown

"The brick walls are there for a reason...to stop the people who don't want it badly enough." - Randy Pausch

nobaq7-Jan-09 6:00

7-Jan-09 6:00

Just look at winhelp32 fulltext- or keyword search.

This is exactly what I want to implement.

Regards,
Niki

Maximilien7-Jan-09 5:42

Maximilien

7-Jan-09 5:42

Use a CListBox,in virtual mode.

If I remember correctly, You will need to manually draw and manage the data, but it will make the CListBox
very fast; once you know how to do it, you will use it everywhere.

You will need to override the CListBox::DrawItem (and maybe the CListBox::MeasureItem )

nobaq7-Jan-09 7:17

why SubclassWindow fails? [modified]

7-Jan-09 7:17

Hi, thank you for this hint.

I've been searching for a while now but I can not find any docs

Do you have a reference, docs, howtos for subclassing CListBox in order to implement a virtual listbox?

Any anyway, how do I query data from my database when "scrolling" very fast? I think i need to minimze my database queries but on the other hand I need to display something while scrolling...

Regards,
Niki

imapi2 cd name

meme817-Jan-09 3:52

meme81

7-Jan-09 3:52

Hi
I've searched documentation and I can't find any answer to my problem.

I'm trying to burn an iso image. I call SHCreateStreamOnFileEx to get a stream from file and pass the stream to DiscFormat2Data->Write.

It all works fine but is there any way to set the name of CD ?
Currently when I'm opening an iso file, for example "NAME_DIGITS_MORE_DIGITS.iso"

my CD is called "NAME". I would like the disc to have the same name as the image.

I saw the function put_VolumeName but I can only use it when I'm creating an image myself.
The iso I'm trying to burn are made by other application Frown | :(

Can someone help me?

SanjaySMK7-Jan-09 3:51

SanjaySMK

7-Jan-09 3:51

In which case CWnd::SubclassWindow(HWND DocumentList) fails, I have locally declared and initialized DocumentList which is used as the the parameter?

Software Developer
Sanjay Khapre

modified on Wednesday, January 7, 2009 10:03 AM

Re: why SubclassWindow fails?

Code-o-mat7-Jan-09 5:05

Code-o-mat

7-Jan-09 5:05

It can fail if it gets a non-valid HWND as parameter (like for example NULL) or if it gets a window that already has something attached to it (instance of another CWnd derived class). These are what i can think of now. But place a breakpoint, and step into that method and just trace down where it fails.

> The problem with computers is that they do what you tell them to do and not what you want them to do. <

replace CMapStringToOb by standard C

RedSonja7-Jan-09 2:28

7-Jan-09 2:28

I have inherited some old code. Our sadistic project management has decided to forbid use of MFC in the hope of being more portable. I replaced all the CStrings with string, now I have got some tricky parts left.
The guy who wrote this used CMapStringToOb in what seems to be a very clever way and I think it is a fine piece of code. But I have to replace it - but with what? I can't use CObjects any more.

I have things like this:
CString csMsgID;
pCommand SACommand; //(which is a CObject)
CMapStringToOb m_knownCommands;
m_knownCommands.Lookup((LPCTSTR)csMsgID, (CObject*&) pCommand)
m_knownCommands.SetAt((LPCTSTR)csMsgID, apFba[i]);

I suppose I could plod through and dream up something complicated and slow, but does anyone have an idea how to do this in an elegant manner? Is this what the type Object is for?

-------------
Bibo ergo sum

CPallini7-Jan-09 2:54

CPallini

7-Jan-09 2:54

RedSonja wrote:
I have inherited some old code. Our sadistic project management has decided to forbid use of MFC in the hope of being more portable.

I'm definitely not an MFC fan, anyway I think your management deserves a kick in the ass.

Must you be stuck with C language or may you use C++?

With C++, you may use STL containers. If you need to use only C, then I suppose you should search for a library offering hashing functions.

Smile | :)

If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler.
-- Alfonso the Wise, 13th Century King of Castile.

This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong.
-- Iain Clarke

[My articles]

RedSonja7-Jan-09 2:58

7-Jan-09 2:58

Oh, yes, we can use STL containers. Which do you recommend?

(I am not really lazy, but I do not usually program this high up in the food chain, and my boss wanted it done in December.)

-------------
Bibo ergo sum

Cedric Moonen7-Jan-09 3:04

Cedric Moonen

7-Jan-09 3:04

I guess using a std::map would do the trick. The problem is that you won't be able to use CObject as a base class, but anyway it is quite ugly anyway. If all the objects in your map have the same base class, then it is fine. If your map needs to store different kind of objects, then probably you need to think the design a bit better...

Cédric Moonen
Software developer

Charting control [v1.5]
OpenGL game tutorial in C++

CPallini7-Jan-09 3:09

CPallini

7-Jan-09 3:09

std::map< std::string, YourRootClass * >

However, as already suggested by Cedric Moonen, maybe better to re-think a bit about the project design (I know it would require experience, time and effort) than mimic the MFC behaviour.

Smile | :)

RedSonja7-Jan-09 3:26

7-Jan-09 3:26

Hmm, you are quite right. Looking at the code a bit harder (I was scared off by CMapStringToOb looking so complicated) I can see he has nothing more than a list of objects derived from the same class, nothing more than that. So I can try with std::list and do the clever bits in a simpler way.

I was hoping to avoid changing every single reference to the things (this is a very large amount of code), but it has to be done, and this week no-one is there to ask what I'm doing. I have redesigned this project quite a lot since it landed on my desk, and this is just about the last untouched corner.

-------------
Bibo ergo sum

Cedric Moonen7-Jan-09 3:32

Cedric Moonen

7-Jan-09 3:32

RedSonja wrote:
I can see he has nothing more than a list of objects derived from the same class, nothing more than that. So I can try with std::list and do the clever bits in a simpler way.

It is a bit more complex than just a list. It is a map which associate each object to a key (being a string). No duplicate key can be found in the map.

To begin working with a std::map, you can look at these tutorials: here[^] or here[^]. You can probably find hundreds of tutorials on the net if you google a bit.

Cédric Moonen
Software developer

Charting control [v1.5]
OpenGL game tutorial in C++

RedSonja7-Jan-09 3:36

7-Jan-09 3:36

Yes, I spotted the key, I need some of those too. Thank you for the tutorials, I shall have a look.

-------------
Bibo ergo sum

XML Writer

amit.code7-Jan-09 1:48

amit.code

7-Jan-09 1:48

Hi.. i want to write xmlwriter function for writing in xml file in c++.Is there any MFC class by which i can implement it or any sample code as reference.
Thanks

amit

Re: XML Writer

Stuart Dootson7-Jan-09 2:02