Archive for May, 2009

How to Change the Display Orientation?

May 10th

Posted by Jijo Raj in Uncategorized

4 comments


Are you using Windows XP? Press Ctrl+Atl+DownArrow, and then Ctrl+Atl+UpArrow. The screen changes its orientation upside down. isn’t it? But how to turn the screen, upside down programmatically?

ChangeDisplayOrientation
Image Courtesy – marieforleo.com


Get the current DEVMODE by calling -EnumDisplaySettings(). Then change orientation by setting DEVMODE.dmDisplayOrientation and calling ChangeDisplaySettings(). Have a look at the code snippet. Code taken from MSDN.

// Get current Device Mode.
DEVMODE DeviceMode = { 0 };
EnumDisplaySettings( NULL,
 ENUM_CURRENT_SETTINGS,
 &DeviceMode );

// Change display mode upside down.
DeviceMode.dmDisplayOrientation = DMDO_180;
ChangeDisplaySettings( &DeviceMode, 0 );

// Sleep for 10 seconds.
Sleep( 10000 );

// Change display mode back.
DeviceMode.dmDisplayOrientation = DMDO_DEFAULT;
ChangeDisplaySettings( &DeviceMode, 0 );


Be careful to restore the display orientation back. Or else ;)


Targeted Audiance – Intermeidate.

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How to Parse Virtual Table?

May 7th

Posted by Jijo Raj in Uncategorized

9 comments

Virtual Table is one of the most fascinating stuff for C++ programmer. Well, did you ever peek into virtual table, which is the real engine of virtual functions?

virtualfunction


The first 4 bytes of an objects points to another pointer which points to virtual table. Casting it to DWORD*, we can parse all virtual functions. Once you get function address, you can get the function name by calling – SymFromAddr(). Have a look at code snippet.

virtualfunction2

#include <ImageHlp.h>
...
// Get list of virtual functions.
void CRabbitDlg::ParseVtable()
{
    // Initialize symbols.
    InitializeSymbols();

    // We are going to parse vtable of CWinApp object.
    DWORD* pBase = (DWORD*)(AfxGetApp());
    DWORD* pVptr = (DWORD*)*pBase;

    // Iterate through VirtualTable.
    DWORD Index = 0;
    DWORD FnAddr = pVptr[Index];
    while( FnAddr )
    {
        // Translate FunctionAddress to FunctionName.
        CString FunctionName;
        GetSymbolNameFromAddr( FnAddr, FunctionName );

        // Format and add to list.
        CString Final;
        Final.Format( _T("%0x - %s"), FnAddr, FunctionName.operator LPCTSTR());
        m_List.AddString( Final );

        // Next function pointer.
        FnAddr = pVptr[++Index];
    }
}

// Initialize Symbol engine.
void CRabbitDlg::InitializeSymbols()
{
    DWORD Options = SymGetOptions();
    Options |= SYMOPT_DEBUG;
    Options |= SYMOPT_UNDNAME; 

    ::SymSetOptions( Options ); 

    // Initialize symbols.
    ::SymInitialize ( GetCurrentProcess(),
                      NULL,
                      TRUE );
}

// Get symbol name from address.
void CRabbitDlg::GetSymbolNameFromAddr( DWORD SymbolAddress, CString& csSymbolName )
{
    DWORD64 Displacement = 0;
    SYMBOL_INFO_PACKAGE SymbolInfo = {0};
    SymbolInfo.si.SizeOfStruct  = sizeof( SYMBOL_INFO );
    SymbolInfo.si.MaxNameLen = sizeof(SymbolInfo.name);

    // Get symbol from address.
    ::SymFromAddr( GetCurrentProcess(),
                   SymbolAddress,
                   &Displacement,
                   &SymbolInfo.si );

    csSymbolName = SymbolInfo.si.Name;
}


Don’t forget to include ImageHlp.lib to project settings.


Targeted Audiance – Intermediate.

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