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Posted 27 Mar 2001

A CListBox with automatic HSCROLL maintenance

, 27 Jun 2001
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Taking the pain out of adding a horizontal scrollbar to a listbox.

A question that seems to come up about once a week in the newsgroup goes something like "I checked the horizontal scroll style in my ListBox, and I don't see any scrollbar. What can I do?"

Horizontal scrolling is poorly understood and even more poorly documented. In order for horizontal scrolling to work, you have to call the SetHorizontalExtent method and set the total width of the horizontal space being used by the entries in the ListBox. If the horizontal extent is larger than the client area of the listbox, the horizontal scrollbar will appear, providing you have selected the horizontal scroll style. You need both to be set to get the effect.

Unfortunately, this is hard to do in the parent window. It involves having to do the computation at every site where you add a string. This is not well object-oriented. So what I've done is create a new class derived from CListBox that incorporates this functionality automatically.

The way I do this is maintain a value which is the maximum width set thus far. Whenever a new string is added, I update the width. When strings are deleted I update the width. I do this by overriding the ResetContent, InsertItem, AddItem, and DeleteString methods.

Note that this works only for non-owner-drawn list boxes. For owner-drawn, it is somewhat easier because you can maintain it in the DrawItem handler.

You can download the sample code, but here's some excerpts. The sample code includes a complete project which demonstrates the scrolling. 

Note that to include this class in your project, you need to include the source file in your project, then delete the .clw file and re-invoke the ClassWizard to get it to see the new class (Microsoft used to allow the importation of classes directly, but this feature seems to have been deleted in the latest versions of Visual Studio). You can then create control variables using the CHListBox class directly in ClassWizard. If you don't do the rebuild of the .clw file, you will have to hand-edit your header file. If you don't know how to do this, check out my essay on Avoiding GetDlgItem.


We need to initialize the width variable in the constructor:

    width = 0;

AddString and InsertString

In the AddString and InsertString handlers, we call a common function to update the width:

int CHListBox::AddString(LPCTSTR s)
    int result = CListBox::AddString(s);
    if(result < 0)
       return result;
    return result;
int CHListBox::InsertString(int i, LPCTSTR s)
    int result = CListBox::InsertString(i, s);
    if(result < 0)
       return result;
    return result;

The updateWidth function is defined as

void CHListBox::updateWidth(LPCTSTR s)
     CClientDC dc(this);

     CFont * f = CListBox::GetFont();

     CSize sz = dc.GetTextExtent(s, _tcslen(s)); += 3 * ::GetSystemMetrics(SM_CXBORDER);
     if( > width)
	 { /* extend */
	  width =;
	 } /* extend */

The reason we add the 3*SM_CXBORDER factor is because we need to allow a bit of additional space to account for the (undocumented and inaccessible) margin that is used to draw the characters. This fudge factor appears to give the best result. To get the correct computation, we have to select the font that is set in the control into the DC.


The ResetContent method is trivial:

void CHListBox::ResetContent()
     width = 0;


The DeleteString operation is expensive because we don't know if we have deleted the widest string. Consequently, we have to evaluate all the strings all over again. Since this can be a bit expensive if we keep calling updateWidth, so the functionality of DC creation and font selection have been moved back into the DeleteString. This could probably be expedited with some inline functions but the code is not very complex, so there seems to be little reason to not duplicated it.

int CHListBox::DeleteString(int n)
     int result = CListBox::DeleteString(n);
     if(result < 0)
	 return result;
     CClientDC dc(this);

     CFont * f = CListBox::GetFont();

     width = 0;
     for(int i = 0; i < CListBox::GetCount(); i++)
	 { /* scan strings */
	  CString s;
	  CListBox::GetText(i, s);
	  CSize sz = dc.GetTextExtent(s);
 += 3 * ::GetSystemMetrics(SM_CXBORDER);
	  if( > width)
	      width =;
	 } /* scan strings */
     return result;

The views expressed in these essays are those of the author, and in no way represent, nor are they endorsed by, Microsoft.

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About the Author

Joseph M. Newcomer
United States United States
PhD, Computer Science, Carnegie Mellon University, 1975
Certificate in Forensic Science and the Law, Duquesne University, 2008

Co-Author, [i]Win32 Programming[/i]

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Comments and Discussions

GeneralA little problem with owner drawn Pin
_kane_16-Nov-06 1:47
member_kane_16-Nov-06 1:47 
GeneralRe: A little problem with owner drawn Pin
_Bids13-May-07 2:00
member_Bids13-May-07 2:00 
GeneralRe: A little problem with owner drawn Pin
_kane_13-May-07 3:24
member_kane_13-May-07 3:24 
GeneralRe: A little problem with owner drawn Pin
_Bids15-May-07 6:57
member_Bids15-May-07 6:57 
GeneralRe: A little problem with owner drawn Pin
_Bids16-May-07 10:48
member_Bids16-May-07 10:48 
GeneralSource with Windows-API functions [modified] Pin
Peter Wucherer26-Jul-06 2:26
memberPeter Wucherer26-Jul-06 2:26 
GeneralInteresting Pin
K(arl)7-Mar-06 4:18
memberK(arl)7-Mar-06 4:18 
An interesting class, which does what it intends too.
A few comments:

  • The use of a non standard naming convention (ie not the hungarian notation[^]) doesn't ease the read of the code.

  • When you select a GDI object in a device context, always re-selected the previously selected object before the destruction of the DC, or you can get GDI leaks. For instance:

    {<br />
       CClientDC dc(this);<br />
       CFont *pMyFont = ::GetStockObject(SYSTEM_FONT);<br />
       CFont *pOldFont = dc.SelectObject(pMyFont);<br />
       [...]<br />
       dc.SelectedObject(pOldFont);<br />
    }<br />

  • In a 'for' statement, it may not be a good idea to use a method in the 'stop condition', because this method is called for each step. Because the item count doesn't change, it would be better to store it in a variable then use this variable in the condition.

  • <hr color=#ADBDFF width=60% height=10%>

    Pull the tapeworm out of your ass
    Fold with us! ¤ flickr

    GeneralRe: Interesting Pin
    Joseph M. Newcomer7-Mar-06 5:54
    memberJoseph M. Newcomer7-Mar-06 5:54 
    GeneralFlame wars Pin
    K(arl)7-Mar-06 6:24
    memberK(arl)7-Mar-06 6:24 
    GeneralRe: Flame wars Pin
    Joseph M. Newcomer7-Mar-06 8:16
    memberJoseph M. Newcomer7-Mar-06 8:16 
    GeneralRe: Flame wars Pin
    K(arl)8-Mar-06 21:42
    memberK(arl)8-Mar-06 21:42 
    GeneralRe: Flame wars Pin
    Joseph M. Newcomer8-Mar-06 22:15
    memberJoseph M. Newcomer8-Mar-06 22:15 
    GeneralRe: Flame wars Pin
    K(arl)9-Mar-06 0:18
    memberK(arl)9-Mar-06 0:18 
    GeneralThanks from me too. Pin
    RancidCrabtree24-Nov-05 6:50
    memberRancidCrabtree24-Nov-05 6:50 
    GeneralGreat ! Pin
    Rodrigo Pinho Pereira de Souza14-Oct-04 10:00
    memberRodrigo Pinho Pereira de Souza14-Oct-04 10:00 
    Generalwhy using "width" param Pin
    Anonymous10-Aug-01 1:02
    memberAnonymous10-Aug-01 1:02 
    GeneralMSDN info on this subject Pin
    Rick York1-Jul-01 14:03
    memberRick York1-Jul-01 14:03 
    QuestionLinker Errors? Pin
    Henry Seeto14-Jun-01 8:06
    memberHenry Seeto14-Jun-01 8:06 
    AnswerRe: Linker Errors? Pin
    Henry Seeto14-Jun-01 8:54
    memberHenry Seeto14-Jun-01 8:54 
    GeneralYes but.... Pin
    Anonymous2-May-01 20:45
    memberAnonymous2-May-01 20:45 
    GeneralRe: Yes but.... Pin
    Dnicholson3-Mar-04 12:16
    memberDnicholson3-Mar-04 12:16 

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