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Beginner's Guide

, 26 May 2005
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Learn about simple DLLs, multithreading and some more stuff.....

Introduction

Dynamic Link Libraries, Multithreading... are all somehow advanced concepts for beginners. But as the word "simple", they are conceptually simple. The aim of this article is to give you some useful technical initiative knowledge on these concepts, especially for the beginners. The article is not moving towards the theoretical definitions of the concept.

Creating a simple DLL

DLL part:

  • Create an empty project on Win32 Dynamic-Link Library.
  • Create a new CPP file in your workspace. (On File View tab in the workspace, right click on the Source Files->Add Files to Folder.. then create a new CPP file).
  • Write your code as follows…
    #include <afxwin.h>
    extern "C" _declspec(dllexport) void SayHello()
    {
        AfxMessageBox(“Hello World”);
    }

Thatzaal all with the DLL code… Build it and get your DLL.

Application part:

  • Create an application wizard (dialog or SDI or MDI…. anything as your wish).
  • Use any message handler to test this DLL… say for example a button handler.
  • Use the following code to load your DLL:
    typedef void (*SayHello) (); // typedef a function pointer
    // load your dll into the memory
    HMODULE hmodule=::LoadLibrary("yourDLLName.dll"); 
    if(hmodule)
    {
        //get your function
        SayHello sm=(SayHello) GetProcAddress(hmodule,"SayHello"); 
        sm(); // thatzaal call your function now
    }
  • Take your DLL to the application’s path.…
  • Build your application now…..

Tips:

  • This is a simple single line code of the above application. It may cause problems if the DLL or the function does not exist…
    GetProcessAddress(LoadLibrary(“yourDLLName.dll”),”SayHello”)();
  • GetProcessAddress() will return the address of the function residing in your DLL. The second parameter is the exact function name that you are going for, so be sure the function name is spelled correctly.

Simple multithreading concept

  1. Create a structure for data transaction between your thread and application. Say for example:
    struct threadinfo{ 
        CString somedata; 
    } info;
  2. Declare a pointer member variable (object) of type CWinThread. Here, CWinThread *m_pthread.
  3. Initiate your thread anywhere in your application as follows:
    m_pthread=AfxBeginThread(functionname,(LPVOID) &info);

    AfxBeginThread() API takes two parameters, the function name (will be your thread) and the necessary information as threadinfo structure.

  4. Write your thread function as:
    UINT functionname(LPVOID param)
    {
        threadinfo *info=(threadinfo *)param;
        CString s=info->somedata;
        // handle your thread code here…
    }
  5. To terminate the thread:
    ::TerminateThread(m_pthread->m_hThread,0);

Minimizing your application to System tray

  1. Create your application in any wizard as your wish (SDI, MDI or dialog).
  2. Add a member variable for NOTIFYICONDATA and CMenu.

    Say for example:

    NOTIFYICONDATA m_traydata; 
    CMenu m_menu;
  3. Add the following code to your OnSysCommand() message handler:
    void CYourDialog::OnSysCommand(UINT nID, LPARAM lParam)
    {
        if(nID==SC_MINIMIZE)
        {
            m_traydata.cbSize=sizeof(NOTIFYICONDATA);
            m_traydata.hWnd =this->m_hWnd;
            m_traydata.uID = 1;
            m_traydata.hIcon=AfxGetApp()->LoadIcon(IDI_YOURICON);
            m_traydata.uCallbackMessage =WM_MY_TRAY;
            strcpy(m_traydata.szTip,"Systray application");
            m_traydata.uFlags=NIF_ICON|NIF_MESSAGE;
            m_menu.DestroyMenu(); // if already exists
            if(!m_menu.LoadMenu(IDR_MENU1)) return;
            Shell_NotifyIcon(NIM_DELETE,&m_traydata); // if already exisits
            If(!Shell_NotifyIcon(NIM_ADD,&m_traydata)) return;
            this->ShowWindow(SW_HIDE);
        }
    }
  4. Define a message as #define WM_MY_TRAY (WM_USER+1) in your header file.
  5. Add a message handler for the message, say OnTrayNotify() as follows:
    • void OnTrayNotify(WPARAM wParam, LPARAM lParam); // in your header file
    • ON_MESSAGE(WM_MY_TRAY,OnTrayNotify) // on your MESSAGE_MAP
    • Following code in your CPP file:
      void CYourDialog::OnTrayNotify(WPARAM wParam, LPARAM lParam)
      {
          UINT uID,uMsg;
          uID=(UINT)wParam;
          uMsg=(UINT)lParam;
          if(uID!=1) return;
          CPoint pt;
          switch(uMsg)
          {
              case WM_LBUTTONDOWN:
              this->ShowWindow(SW_SHOW);
              this->ShowWindow(SW_NORMAL);
              Shell_NotifyIcon(NIM_DELETE,&m_traydata);
              break;
              case WM_RBUTTONDOWN:
              case WM_CONTEXTMENU:
              GetCursorPos(&pt);
              OnTrayRButton(pt);
              break;
          }
          return;
      }
  6. Add a member function called OnTrayRButton(CPoint point):
    void CYourDialog::OnTrayRButton(CPoint point)
    {
        // assuming that the IDR_MENU1 is having atleast one submenu
        m_menu.GetSubMenu(0)->TrackPopupMenu(TPM_BOTTOMALIGN| 
        TPM_LEFTBUTTON| TPM_RIGHTBUTTON,point.x,point.y,this);
    }
  7. The OnDestroy method:
    void CYourDialog::OnDestroy() 
    {
        CDialog::OnDestroy();
        Shell_NotifyIcon(NIM_DELETE,&m_traydata);
    }
  8. Thatzaal, you are having your application in systray now.

Popup menu for your application

Method 1:

  • Add a member variable for CMenu (say for e.g.. m_menu);
  • Load menu resource into your menu member m_menu.LoadMenu(IDR_MENU1);
  • Add context menu handler to your application (WM_CONTEXTMENU).
    void CYourDlg:: OnContextMenu(CWnd* pWnd, CPoint point) 
    { 
        m_menu.GetSubMenu(0)->TrackPopupMenu(TPM_RIGHTBUTTON,
                                           point.x,point.y,this);
    }

Method 2:

  • Add a member variable for CMenu ( say for e.g.. m_menu);
  • Add context menu handler to your application (WM_CONTEXTMENU).
    void CYourDlg:: OnContextMenu(CWnd* pWnd, CPoint point) 
    { 
        m_menu.DestroyMenu(); // Destroy the old menu if any.
        m_menu.CreatePopupMenu();
        m_menu.AppendMenu(MF_STRING,1000,"item 1");
        m_menu.AppendMenu(MF_SEPARATOR);
        m_menu.AppendMenu(MF_STRING,1001,"item 2");
        m_menu.AppendMenu(MF_STRING,1002,"item 3");
        m_menu.AppendMenu(MF_POPUP,(UINT) m_menu2.m_hMenu,”sub menu”);
        m_menu.TrackPopupMenu(TPM_RIGHTBUTTON,point.x,point.y,this);
    }
  • 1000, 1001, 1002 are the command IDs for the menu items. Use this ID to identify your menu item in wParam of WM_COMMAND message.
  • MF_POPUP is used to attach a submenu to your popup menu. In this case command ID parameter will take a menu handle instead of an ID. Menu handle can be any other menu you have created like m_menu.

About CPtrList class

  • CPtrList is a pointer list class (linked list). It can hold any number of items in the list dynamically.
  • To add an item to the list, call CPtrList::AddTail() / CPtrList:::AddHead() / CPtrList::InsertAfter() / CPtrList::InsertBefore() /CPtrList::SetAt().
  • The items in the CPtrList are void* type. Type cast your objects to void* while adding it to the list.
  • To retrieve an item from the list, use CPtrList::GetHead() / CPtrList::GetTail() / CPtrList::GetAt() / CPtrList:::GetNext() / CPtrList::GetPrev().
  • While retrieving items from the list, type cast the void type to your object type.
  • Use POSITION handle to parse the list. It is not an index. It is the handle that points to your objects in the list.
  • All the elements in your list will be handled with the POSITION handle only.
  • To find an item in the list you can use both the index and the POSITION. CPtrList::FindIndex(index) will return the POSTION value. CPtrList::Find(void *) will return the item.
  • CPtrList::GetNext(POSITION) will return the current object and will increment the position value to the next. POSITION is the reference parameter.
  • To remove an item / all item from the list: CPtrList::RemoveAt() / CPtrList::RemoveAll().
  • Take care while allocating and freeing the memory of your objects while adding and removing it from the list. It is your responsibility to delete the allocated objects. CPtrList won't delete the objects while removing it from the list.

    Example:

    // Adding an object to the list
    // Should be deleted. Caution: Memory Leak
    m_objList.AddTail((void *) new CPoint(2,2)); 
    // Traversing a CPtrList; and assigning value to the objects 
    POSITION pos=m_objList.GetHeadPosition(); 
    while(pos)
    {
       CPoint *obj=(CPoint *)m_objList.GetNext(pos);
       obj->x=10;obj->y=10;
    }
    // Removing the objects from the list
    POSITION pos=m_objList.GetHeadPosition(); 
    while(pos)
    {
       CPoint *obj=(CPoint *)m_objList.GetNext(pos);
       delete obj;
    }
    m_objList.RemoveAll();

About CListCtrl

  • Having gridlines:
    CListCtrl::SetExtendedStyle(LVS_EX_FULLROWSELECT|LVS_EX_GRIDLINES);
  • Adding columns:
    CListCtrl::InsertColumn(index,title,alignment,<title length>*25,-1)

    Alignment - LVCFMT_LEFT, LVCFMT_RIGHT, LVCFMT_CENTER

  • Setting width for columns:
    CListCtrl::SetColumnWidth(index,size);
  • Inserting items into the list:
    CListCtrl::InsertItem(index,””);
    CListCtrl::SetItemText(index,column,item_text);
  • Getting items from the list:
    CString txt=CListCtrl::GetItemText(item,column);
  • Getting selected items from the list:
    POSITION pos=CListCtrl:: GetFirstSelectedItemPosition();
    while(pos)
    {
       int item=CListCtrl::GetNextSelectedItem(pos);
       CString txt=CListCtrl::GetItemText(item,column);
    }
  • Set focus to a row:
    CListCtrl::SetItemState(index,LVIS_FOCUSED,LVIS_FOCUSED);
  • Delete all items in the list:
    CListCtrl::DeleteAllItems();

About Database connection…

  • Opening a database:
    CDatabase db;
    db.OpenEx("DRIVER=Microsoft Access Driver (*.mdb);DBQ=mydatabase.mdb;")
  • Having a recordset for the database:
    CRecordset rs;
    rs.m_pDatabase=&db;
  • Getting values from a recordset:
    rs.GetFieldValue(index,CString&);
  • Getting total number of records:
    rs.GetRecordCount();
  • Parsing full recordset of a database:
    if(rs.GetRecordCount()==0) return; 
    
    rs.MoveFirst();
    
    for(int i=0; i<rs.GetRecordCount(); i++)
    
    {
        CString emp_no,emp_name,;
        rs.GetFieldValue(0,emp_no);
        rs.GetFieldValue(1,emp_name);
        MessageBox(emp_no+” “+emp_name);
        rs.MoveNext(); 
    }

(to be continued...)

Conclusion

I am not telling that these are the full concepts indicated by the titles. But these are the basics. The article may not cover the full area over the concepts. None of the articles can satisfy one's expectations. But, each article should be a seed for your technical growth. Thus, I believe that this would be a seed. Thank you all.

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About the Author

Naren Neelamegam
Software Developer
India India
Naren started coding during 1999 with FORTRAN, then COBOL, C, C++, VC++ ..... C#, Java, ASP so on, till today. He claims himself as techie who loves coding, but he is not even sure which technology or platform he loves, most of the time Windows, some time WinCE, some time Linux, nowadays Android and embedded platforms. He is not a DB expert, but still can do some query stuffs with Oracle, SQL Server, MySQL. He strongly believes that C/C++ is a must for all programmers, "if you know C/C++, you can do programming on any language". He is an electronic gadget guy who likes to buy small gadgets all the time, at least he will do window shopping on a gadget shop. His interest always have been with Automation in any form, call it a little automated program sitting in his Laptop or a home automation program runs on his mobile. He was owning a website called www.narenn.com which is not active now as he forgot to renew it and still thinking of renewing it "tomorrow". Apart from coding, he likes to do...???

Comments and Discussions

 
GeneralProblem with closing tray menu PinmemberMember 45806386-Nov-08 10:51 
AnswerRe: Problem with closing tray menu PinmemberNaren Neelamegam3-Nov-09 19:59 
Generalsamples PinmemberSunilkumarmn28-Mar-07 23:56 
Questionnice article but what about win32!!! Pinmemberdfgdiewocxn27-Dec-06 1:53 
GeneralProblem With Making Loader :( Pinmemberridder22-Sep-06 0:18 
GeneralVery Nice PinmemberPravinSingh15-May-06 22:13 
Generalgood job Pinmembermousewolf9-Jul-05 14:50 
GeneralNice, but... PinmemberGeert van Horrik26-May-05 1:40 
GeneralRe: Nice, but... PinmemberNareen Neelamegam26-May-05 1:52 
GeneralRe: Nice, but... PinmemberThatsAlok26-May-05 19:07 
GeneralGr8 Job PinmemberNMos26-May-05 1:13 

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