C / C++ / MFC

void CMyDlg::OnSysCommand(UINT nID, LPARAM lParam) 
{
if (nID == SC_CONTEXTHELP)
{
	m_bContextHelp = TRUE;
}
CDialog::OnSysCommand(nID, lParam);
if (nID == SC_CONTEXTHELP)
{
	m_bContextHelp = FALSE;
}
}

BOOL CMyDialog::OnHelpInfo(HELPINFO* pHelpInfo)
// this function is called when the user presses the F1 key or clicks on
// the '?' title bar icon and then on a control
{
    short state = GetKeyState (VK_F1);
    if (state & 0x80)   // F1 key is down, get help for the dialog
        return CDialog::OnHelpInfo(pHelpInfo);
    // F1 key not down, get help for specific control
    WinHelp (pHelpInfo->dwContextId, HELP_CONTEXTPOPUP);
    return TRUE;
}

#if !defined(_W64)
#if !defined(__midl) && (defined(_X86_) || defined(_M_IX86)) && _MSC_VER >= 1300
#define _W64 __w64
#else
#define _W64
#endif
#endif

//
// The INT_PTR is guaranteed to be the same size as a pointer.  Its
// size with change with pointer size (32/64).  It should be used
// anywhere that a pointer is cast to an integer type. UINT_PTR is
// the unsigned variation.
//
// __int3264 is intrinsic to 64b MIDL but not to old MIDL or to C compiler.
//
#if ( 501 < __midl )

    typedef [public] __int3264 INT_PTR, *PINT_PTR;
    typedef [public] unsigned __int3264 UINT_PTR, *PUINT_PTR;

    typedef [public] __int3264 LONG_PTR, *PLONG_PTR;
    typedef [public] unsigned __int3264 ULONG_PTR, *PULONG_PTR;

#else  // midl64
// old midl and C++ compiler

#if defined(_WIN64)
    typedef __int64 INT_PTR, *PINT_PTR;
    typedef unsigned __int64 UINT_PTR, *PUINT_PTR;

    typedef __int64 LONG_PTR, *PLONG_PTR;
    typedef unsigned __int64 ULONG_PTR, *PULONG_PTR;

    #define __int3264   __int64

#else
    typedef _W64 int INT_PTR, *PINT_PTR;
    typedef _W64 unsigned int UINT_PTR, *PUINT_PTR;

    typedef _W64 long LONG_PTR, *PLONG_PTR;
    typedef _W64 unsigned long ULONG_PTR, *PULONG_PTR;

    #define __int3264   __int32

#endif
#endif // midl64