Need help solving a issue in listbox-CodePudding

I'm still learning c mfc and my question is: how can I get the CurSel of 2 listbox as the number, then add them and print the result? the result displays a weird 659998896 number instead of 2. What have I done wrong here?

BOOL CEngravingCalculatorDlg::OnInitDialog(){
    CListBox* emplistbox1 = static_cast<CListBox*>(GetDlgItem(IDC_LIST1));
    emplistbox1->AddString(L"1");
    emplistbox1->SetCurSel(0);

    CListBox* emplistbox3 = static_cast<CListBox*>(GetDlgItem(IDC_LIST3));
    emplistbox3->AddString(L"1");
    emplistbox3->SetCurSel(0);
    }

void CEngravingCalculatorDlg::OnBnClickedButton1()
{
   CListBox* emplistbox1 = static_cast<CListBox*>(GetDlgItem(IDC_LIST1));
   CListBox* emplistbox3 = static_cast<CListBox*>(GetDlgItem(IDC_LIST3));
   int num1 = emplistbox1->GetCurSel();
   int num2 = emplistbox3->GetCurSel();
   int equal = num1   num2;
   CString str;
   str.Format(_T("%d", equal));
    GetDlgItem(IDC_Display)->SetWindowTextW(str);
}

CodePudding user response：

_T is a macro that takes only a single parameter. Because of a typo, you've given it two parameters. The second one is ignored and effectively lost. This means your format call is only getting a single parameter, and you're seeing undefined behavior. Fix it with:

str.Format(_T("%d"), equal);

P.S. This means your error had absolutely nothing to do with the listbox.

CodePudding user response：

See this snippet. GetCurSel() is used to get the cursor position and not the content. Use GetText() to get the content of the Listbox.

void CEngravingCalculatorDlg::OnBnClickedButton1()
{
    CListBox* emplistbox1 = static_cast<CListBox*>(GetDlgItem(IDC_LIST1));
    CListBox* emplistbox3 = static_cast<CListBox*>(GetDlgItem(IDC_LIST3));
    int num1 = emplistbox1->GetCurSel();
    int num2 = emplistbox3->GetCurSel();

    CString ItemSelected1, ItemSelected2;
    if (num1 != LB_ERR && num2 != LB_ERR)   {
        emplistbox1->GetText(num1, ItemSelected1);      
        emplistbox3->GetText(num2, ItemSelected2);      

        int equal = atoi(CStringA(ItemSelected1).GetString())   atoi(CStringA(ItemSelected2).GetString());
        CString str;
        str.Format(L"%d", equal);
        SetDlgItemText(IDC_Display, str);
    }

}