Virtual destructor

One of the common C++ interview question is what is virtual destructor? Or what is the use of virtual destructor?

You are assigning a derived class object to a base class pointer and deleting the base class pointer.

If the base class destructor is not declared as virtual, then derived class destructor won’t get called.

If you are deleting some variables allocated heap memory in derived class destructor, then it will cause memory leak.

// CPPSamples.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"
#include <iostream>
#include <conio.h>
using namespace std;
class Base
{
    public:
    Base()
    {
        cout<<"\n Base class Constructor\r\n";
    }
    ~Base()
    {
        cout<<"\n Base class Destructor\r\n";
    }

};
class Derived:Base
{
public:
    Derived()
    {
        cout<<"\n Derived class Constructor\r\n";
    }
    ~Derived()
    {
        cout<<"\n Derived class Destructor\r\n";
    }
};

int _tmain(int argc, _TCHAR* argv[])
{
    Base *ptr=(Base*)new Derived();
    delete ptr;
    getch();
    return 0;
}

If the base class Destructor is virtual then,

// CPPSamples.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"
#include <iostream>
#include <conio.h>
using namespace std;
class Base
{
    public:
    Base()
    {
        cout<<"\n Base class Constructor\r\n";
    }
    virtual ~Base()
    {
        cout<<"\n Base class Destructor\r\n";
    }

};
class Derived:Base
{
public:
    Derived()
    {
        cout<<"\n Derived class Constructor\r\n";
    }
    ~Derived()
    {
        cout<<"\n Derived class Destructor\r\n";
    }
};

int _tmain(int argc, _TCHAR* argv[])
{
    Base *ptr=(Base*)new Derived();
    delete ptr;
    getch();
    return 0;
}

Rollback is not working in PhpMyAdmin MySQL

Once I had problem, in rollback my changes in  MySQL.
I tried disabling autocomit. But problem was not resolved.

/* disable autocommit */
$mysqli->autocommit(FALSE);

$mysqli->rollback();
mysql_query("ROLLBACK");


Then finally, I found the actual problem.
By default in PhpMyadmin table type is MyISAM. Rollback will not work in MyISAM.

Then I changed the table in to InnoDB, It worked!!!

Chat Client Cheater

Your boss and your girlfriend can able to monitor you, using the chat client installed in your computer. If you didn’t press any key or move your mouse for long time then chat client status will automatically goes to “Away”. Using that, they can find, when you are coming to or leaving the office and how much time you are spending in cafeteria.

In most of companies, they have chat clients for internal communication.  Mostly they use Microsoft Lync or some other XMPP Chat client similar to G-Talk.  We can cheat them, by sending fake mouse movement.

I have created an application, which sends the fake mouse events. So I always switch off my monitor alone and go to cafeteria or leave office early. But if anyone can, switch on the monitor and use my computer. My company policy doesn’t allow me to leave my desk without locking my computer.  So if someone touches (Mouse move or Key Press) my computer it will automatically get locked.  You can also set a secret key to deactivate this application and not to get locked when you came back.

 Source Code in VC++ (MFC):

HHOOK g_hDesktopHook; // Also declared global
HHOOK g_hKeyboardHook; // Also declared global
BOOL g_bMouseEvent=TRUE;
CWinThread *g_MouseThread=NULL;
int g_nXPos=0;
int g_nYpos=0;

void SendMouseMoveMessage()
{
    INPUT ip;

    ip.type = INPUT_MOUSE;
    ip.mi.dx = 0;
    ip.mi.dy = 0;
    ip.mi.mouseData = 0;
    ip.mi.dwFlags = (MOUSEEVENTF_MOVE || MOUSEEVENTF_ABSOLUTE);
    ip.mi.time = 0;
    ip.mi.dwExtraInfo = GetMessageExtraInfo();
    SendInput(1, &ip, sizeof(ip));
}
UINT MouseMoveThread(LPVOID lpMsg)
{
    while(g_bMouseEvent)
    {
        SendMouseMoveMessage();
        Sleep(5000);
    }
    return 0;
}
LRESULT CALLBACK MouseProc(int nCode, WPARAM wParam, LPARAM lParam)
{
    if(nCode < 0)
        return CallNextHookEx(g_hDesktopHook, nCode, wParam, lParam);
    KBDLLHOOKSTRUCT *msg = (KBDLLHOOKSTRUCT*)lParam;
    if(nCode == HC_ACTION)
    {

        if(wParam == WM_LBUTTONDOWN ||wParam == WM_RBUTTONDOWN ||wParam ==WM_MOUSEMOVE )
        {
            LPMOUSEHOOKSTRUCT lpMouse=NULL;
            lpMouse=(LPMOUSEHOOKSTRUCT)lParam;
            if(lpMouse)
            {
                if(g_nXPos==0 && g_nYpos==0)
                {
                    g_nXPos=lpMouse->pt.x;
                    g_nYpos=lpMouse->pt.y;
                }
                if(g_nXPos!=lpMouse->pt.x||    g_nYpos!=lpMouse->pt.y)
                {
                    g_bMouseEvent=FALSE;
                    //Lock Computer
                    LockWorkStation() ;
                    AfxGetMainWnd()->PostMessage(WM_CLOSE);
                }
            }
        }
        else if (  wParam == WM_KEYUP || wParam ==WM_KEYDOWN) 
        {
            if ( msg->vkCode =='U' ) 
            {
                //If U is pressed Remain Unlocked and Exit 
                //Else lock computer
                g_bMouseEvent=FALSE;
                AfxGetMainWnd()->PostMessage(WM_CLOSE);

            }
            else
            {
                g_bMouseEvent=FALSE;
                LockWorkStation() ;
                AfxGetMainWnd()->PostMessage(WM_CLOSE);
                
            }
        }   
    }

    return CallNextHookEx(g_hDesktopHook, nCode, wParam, lParam);
}
void CChatClietCheaterDlg::OnBnClickedStart()
{
    Sleep(2000);
    if((g_hDesktopHook = SetWindowsHookEx(WH_MOUSE_LL, MouseProc, NULL, 0)) == NULL)
    {
    // hook failed...
    }
    
    if((g_hKeyboardHook = SetWindowsHookEx(WH_KEYBOARD_LL, MouseProc, NULL, 0)) == NULL)
    {
        //  hook failed....
    }
    g_MouseThread=AfxBeginThread(MouseMoveThread,NULL);
    
}

void CChatClietCheaterDlg::OnDestroy()
{
    CDialogEx::OnDestroy();
    g_bMouseEvent=FALSE;
    if(g_hDesktopHook)
        UnhookWindowsHookEx(g_hDesktopHook);

    WaitForSingleObject(g_MouseThread->m_hThread,5000);
}

Update: 

I created it as a software application. for details please visit 

http://mykodetips.blogspot.com/2013/02/chat-client-cheater-software.html 

How to make names in MS Excel Proper?

Proper(Text) - first letter caps


Once I had list of names in MS Excel, all are in small letters.
I want the first letter alone in the Capital letter.

Then I found PROPER() Capitalizes the first letter in a string and converts all other letters to lowercase letters.

Syntax

PROPER(Text)

About Me and My blog

Dear Friends,

I like to share my experience in computer programming in thin blog.
I have experience in VC++, VBA, PHP, MySQL and .net.

Soon I will post the issues I faced when I used some popular applications and in programming with solutions.