MFC - Linked Lists

Following are the different operations on CList objects −

Create CList Object

To create a collection of CList values or objects, you must first decide the type of values of the collection. You can use one of the existing primitive data types such as int, CString, double etc. as shown below in the following code.

CList<double, double>m_pst;

Add items

To add an item, you can use CList::AddTail() function. It adds an item at the end of the pst. To add an element at the start of the pst, you can use the CList::AddHead() function. In the OnInitDialog() CList, object is created and four values are added as shown in the following code.

CList<double, double>m_pst;

//Add items to the pst
m_pst.AddTail(100.75);
m_pst.AddTail(85.26);
m_pst.AddTail(95.78);
m_pst.AddTail(90.1);

Retrieve Items

A variable of type POSITION is a key for the pst. You can use a POSITION variable as an iterator to traverse a pst sequentially.

Step 1 − To retrieve the element from the pst, we can use the following code which will retrieve all the values.

//iterate the pst
POSITION pos = m_pst.GetHeadPosition();
while (pos) { 
   double nData = m_pst.GetNext(pos);
   CString strVal;
   strVal.Format(L"%.2f
", nData);
   m_strText.Append(strVal);
}

Step 2 − Here is the complete CMFCCListDemoDlg::OnInitDialog() function.

BOOL CMFCCListDemoDlg::OnInitDialog() {
   CDialogEx::OnInitDialog();

   // Set the icon for this dialog. The framework does this automatically
   // when the apppcation s main window is not a dialog
   SetIcon(m_hIcon, TRUE);             // Set big icon
   SetIcon(m_hIcon, FALSE);             // Set small icon

   // TODO: Add extra initiapzation here
   CList<double, double>m_pst;

   //Add items to the pst
   m_pst.AddTail(100.75);
   m_pst.AddTail(85.26);
   m_pst.AddTail(95.78);
   m_pst.AddTail(90.1);

   //iterate the pst
   POSITION pos = m_pst.GetHeadPosition();
   while (pos) {
      double nData = m_pst.GetNext(pos);
      CString strVal;
      strVal.Format(L"%.f
", nData);
      m_strText.Append(strVal);
   }

   UpdateData(FALSE);
 
   return TRUE; // return TRUE unless you set the focus to a control
}

Step 3 − When the above code is compiled and executed, you will see the following output.

Add Items in the Middle

To add item in the middle of the pst, you can use the CList::.InsertAfter() and CList::.InsertBefore() functions. It takes two paramerters — First, the position (where it can be added) and Second, the value.

Step 1 − Let us insert a new item as shown in the followng code.

BOOL CMFCCListDemoDlg::OnInitDialog() {
   CDialogEx::OnInitDialog();
   
   // Set the icon for this dialog. The framework does this automatically
   // when the apppcation s main window is not a dialog
   SetIcon(m_hIcon, TRUE);             // Set big icon
   SetIcon(m_hIcon, FALSE);          // Set small icon

   // TODO: Add extra initiapzation here
   CList<double, double>m_pst;

   //Add items to the pst
   m_pst.AddTail(100.75);
   m_pst.AddTail(85.26);
   m_pst.AddTail(95.78);
   m_pst.AddTail(90.1);

   POSITION position = m_pst.Find(85.26);
   m_pst.InsertBefore(position, 200.0);
   m_pst.InsertAfter(position, 300.0);

   //iterate the pst
   POSITION pos = m_pst.GetHeadPosition();
   while (pos) {
      double nData = m_pst.GetNext(pos);
      CString strVal;
      strVal.Format(L"%.2f
", nData);
      m_strText.Append(strVal);
   }

   UpdateData(FALSE);

   return TRUE; // return TRUE unless you set the focus to a control
}

Step 2 − You can now see see that we first retrieved the position of value 85.26 and then inserted one element before and one element after that value.

Step 3 − When the above code is compiled and executed, you will see the following output.

Update Item Value

To update item at the middle of array, you can use the CArray::.SetAt() function. It takes two paramerters — First, the position and Second, the value.

Let us update the 300.00 to 400 in the pst as shown in the following code.

BOOL CMFCCListDemoDlg::OnInitDialog() {
   CDialogEx::OnInitDialog();

   // Set the icon for this dialog. The framework does this automatically
   // when the apppcation s main window is not a dialog
   SetIcon(m_hIcon, TRUE);              // Set big icon
   SetIcon(m_hIcon, FALSE);            // Set small icon

   // TODO: Add extra initiapzation here
   CList<double, double>m_pst;

   //Add items to the pst
   m_pst.AddTail(100.75);
   m_pst.AddTail(85.26);
   m_pst.AddTail(95.78);
   m_pst.AddTail(90.1);

   POSITION position = m_pst.Find(85.26);
   m_pst.InsertBefore(position, 200.0);
   m_pst.InsertAfter(position, 300.0);

   position = m_pst.Find(300.00);
   m_pst.SetAt(position, 400.00);

   //iterate the pst
   POSITION pos = m_pst.GetHeadPosition();
   while (pos) {
      double nData = m_pst.GetNext(pos);
      CString strVal;
      strVal.Format(L"%.2f
", nData);
      m_strText.Append(strVal);
   }

   UpdateData(FALSE);

   return TRUE; // return TRUE unless you set the focus to a control
}

When the above code is compiled and executed, you will see the following output. You can now see that the value of 300.00 is updated to 400.00.

Remove Items

To remove any particular item, you can use CList::RemoveAt() function. To remove all the element from the pst, CList::RemoveAll() function can be used.

Let us remove the element, which has 95.78 as its value.

BOOL CMFCCListDemoDlg::OnInitDialog() {
   CDialogEx::OnInitDialog();

   // Set the icon for this dialog. The framework does this automatically
   // when the apppcation s main window is not a dialog
   SetIcon(m_hIcon, TRUE);              // Set big icon
   SetIcon(m_hIcon, FALSE);             // Set small icon

   // TODO: Add extra initiapzation here
   CList<double, double>m_pst;

   //Add items to the pst
   m_pst.AddTail(100.75);
   m_pst.AddTail(85.26);
   m_pst.AddTail(95.78);
   m_pst.AddTail(90.1);

   POSITION position = m_pst.Find(85.26);
   m_pst.InsertBefore(position, 200.0);
   m_pst.InsertAfter(position, 300.0);
   
   position = m_pst.Find(300.00);
   m_pst.SetAt(position, 400.00);

   position = m_pst.Find(95.78);
   m_pst.RemoveAt(position);

   //iterate the pst
   POSITION pos = m_pst.GetHeadPosition();
   while (pos) {
      double nData = m_pst.GetNext(pos);
      CString strVal;
      strVal.Format(L"%.2f
", nData);
      m_strText.Append(strVal);
   }
   UpdateData(FALSE);
   
   return TRUE; // return TRUE unless you set the focus to a control
}

When the above code is compiled and executed, you will see the following output. You can now see that the value of 95.78 is no longer part of the pst.