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Example of CListCtrl::SortItems(...) in MSDN

, 27 Feb 2002
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The given example in the documentation of CListCtrl::SortItems(...) shows us exactly the WRONG way of using the function.
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If we look at the documentation of CListCtrl::SortItems(...) in MSDN we find the following example of how to sort the items in reverse alphabetical order:

// Sort the item in reverse alphabetical order.
static int CALLBACK 
MyCompareProc(LPARAM lParam1, LPARAM lParam2, LPARAM lParamSort)
{
   // lParamSort contains a pointer to the list view control.
   CListCtrl* pListCtrl = (CListCtrl*) lParamSort;
   CString    strItem1 = pListCtrl->GetItemText(lParam1, 0);
   CString    strItem2 = pListCtrl->GetItemText(lParam2, 0);

   return strcmp(strItem2, strItem1);
}

void snip_CListCtrl_SortItems()
{
   // The pointer to my list view control.
   extern CListCtrl* pmyListCtrl;

   // Sort the list view items using my callback procedure.
   pmyListCtrl->SortItems(MyCompareProc, (LPARAM) pmyListCtrl);
}
This approach obviously does not work and here is why: The parameters of MyCompareProc(...) - lParam1 and lParam2 are not the index of the items but their 32-bit associated value.

There is a second problem: even if we set the 32-bit associated value of each item to be the same as the item's index this example will still not work. This is because the items will shift positions after each call to MyCompareProc(...) and the 32-bit associated values will no longer represent the item's index.

The function CListCtrl::SortItems(...) is only usefull if we store a pointer in the 32-bit associated value and we want to sort the items by some value that comes from that pointer.

One easy way of implementing reverse alphabetical sort in CListCtrl derived class is using an STL set:

#pragma warning(disable : 4786)
#include <functional>
#include <set>

struct LVITEM_less : public std::binary_function<LVITEM*, LVITEM*, bool>
{
    bool operator()(const LVITEM* pItem1, const LVITEM* pItem2) const
    {
        CString strItem1(pItem1->pszText);
        CString strItem2(pItem2->pszText);

        return (strItem1 < strItem2);
    }
};

void CSortableListCtrl::SortItemsDescending()
{
    // Sort all items in descending aphabetical order using an STL set
    typedef std::set<LVITEM*, LVITEM_less> ItemSet;
    ItemSet setItems;
    int iCount = GetItemCount();
    for (int i = 0; i < iCount; i++)
    {
        LVITEM* pLVI = new LVITEM();
        ::memset(pLVI, 0, sizeof(LVITEM));
        pLVI->iItem = i;
        pLVI->mask = LVIF_IMAGE | LVIF_INDENT | LVIF_PARAM | LVIF_STATE | LVIF_TEXT;
        pLVI->pszText = new TCHAR[1024];
        pLVI->cchTextMax = 1024;
        GetItem(pLVI);

        setItems.insert(pLVI);
    }

    // Remove all items from the list control
    DeleteAllItems();

    // Put the items back in the list control in reverse order
    int iIndex = 0;
    for (ItemSet::reverse_iterator it = setItems.rbegin(); it != setItems.rend(); ++it)
    {
        (*it)->iItem = iIndex++;
        InsertItem(*it);
        delete [] (*it)->pszText;
        delete *it;
    }
}

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About the Author

Ivor S. Sargoytchev
Software Developer (Senior)
Canada Canada
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Comments and Discussions

 
QuestionIgnoring the repeatations PinmemberAt_work3-Jun-08 22:06 
QuestionExplanation Pinmembertom groezer25-May-07 12:08 
GeneralMuch simpler solution!! PinmemberAndy Bray3-Aug-06 23:30 
Generalauthor does not understand how to use the sort issue at all Pinmemberincludeh1016-Jun-06 4:19 
GeneralI use it with NO problem PinmemberRancidCrabtree24-Aug-05 9:36 
GeneralRe: I use it with NO problem PinmemberLeonhardt Wille11-May-06 21:29 
GeneralError correction of MSDN Sample... Pinmembermartin.compel22-May-03 6:18 
GeneralRe: Error correction of MSDN Sample... PinsussAnonymous27-Aug-03 5:23 
GeneralRe: Error correction of MSDN Sample... PinmemberPriya_Sundar16-Apr-08 2:50 
GeneralRe: Error correction of MSDN Sample... PinsussAnonymous15-Oct-03 3:58 
GeneralRe: Error correction of MSDN Sample... Pinmembercibercop16-Aug-05 5:55 
Generalmore simple example . Pinmemberradezz15-Sep-05 12:28 
QuestionHow to: make lParam1 and lParam2 being indices PinmemberGeert Delmeiren8-Apr-02 1:14 
AnswerRe: How to: make lParam1 and lParam2 being indices Pinmemberrsmenezes25-Aug-02 7:20 
GeneralAlternative to slow SortItems PinmemberTim Kosse28-Feb-02 7:19 
GeneralRe: Alternative to slow SortItems PinmemberIvor S. Sargoytchev28-Feb-02 7:26 
GeneralThis was the Introduction here some tips... PinmemberKarstenK28-Feb-02 0:29 
QuestionSolution? PinmemberDavide Calabro27-Feb-02 21:33 
AnswerRe: Solution? PinmemberChris Maunder28-Feb-02 4:33 
GeneralSorry... PinmemberDavide Calabro28-Feb-02 5:37 
GeneralRe: Solution? PinmemberDavid Wulff28-Feb-02 13:30 

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