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exHelper helps you to find easy and quickly the answers and the source code for your questions regarding the usage of our UI components.
eXImages loads and compress pictures, icons or files to BASE64 strings.
EBN generates EBN files, that are used to skin or to change the visual appearance of UI components.
- Gallery provides a list of already built EBN templates to skin your UI controls.
eXCRD generates and builds custom layouts for cells/nodes, items/rows or columns/fields.
eBinder connects a DataSet object, to table-view components such as eXGrid, eXG2antt, eXTree, eXList, eXComboBox, and so on.

Free Components

exPrint is an advanced printing system specifically to bring your User Interface to the printed page.
exTransparent applies transparency to your forms.
exZoom magnifies your screen.
exHTTP, Exontrol's exHTTP is a HTTP client component that provides easy interface to the HTTP (Hypertext Transfer Protocol) protocol.
exInbox is a simple-to-use POP3 client library that allows mail readers to connect to many POP servers and manage email.
exChange is a simple-to-use FXP client library that performs currency conversions.

Visual Basic

The properties Screen.TwipsPerPixelX and Screen.TwipsPerPixelY are missing in MS Access, is there any way to replace them?
What should I do if my control is flickering ?
How to make your form semitransparent?
How can I get the list of processes?
How can I display a files/folder view explorer to my form?

C++

I am looking for a tool that counts the number of lines in my project?
How do I get the file version entry in the resource?
Fills a rectangle using a transparent color.
How do I create a shortcut file by code?
How do I move my dialog without clicking in the caption area?
How to change the dialog's background?
How to convert a VARIANT to a string?
How to find the name for interfaces that a COM object implements?
I have a picture file, and all that I need is an object that handles that picture. What can I do?
How can I load a picture from resource?
I have a IPictureDisp pointer, and want to draw the picture to a device context.
I have a bitmap and I want to draw it using a transparent color.
I don't want to use AtlAxCreateWindow, AtlAxCreateWindow2 in order to host my control ,because these are implemented in ATL.DLL file.
Why the Invalidate method doesn't refresh my window, right after calling?
I have a pointer and I want to know if it points to a valid memory area. What should I do ?
How CoCreateInstance API works?
How can I retrieve the clipboard data?
Is there any equivalent function for VB Round function in C++?
How can I have the Integer Division Operator "\" in my C++ program?
How do I load icons using more than 16 colors to my image list?
How do I declare a pointer to a function in a C++ class (term does not evaluate to a function)?
Saving EMF format to a picture file
How do I find the intersection of two rectangles?

Visual Basic

The properties Screen.TwipsPerPixelX and Screen.TwipsPerPixelY are missing in MS Access, is there any way to replace them?

The article ACC2000, How to convert Twips to Pixels, explains what you have to do. Anyway, here's the Twips2Pixels function that converts X and Y twips coordinates to pixels coordinates.

Private Declare Function GetDC Lib "user32" (ByVal hwnd As Long) As Long Private Declare Function ReleaseDC Lib "user32" (ByVal hwnd As Long, ByVal hDC As Long) As Long Private Declare Function GetDeviceCaps Lib "gdi32" (ByVal hDC As Long, ByVal nIndex As Long) As Long Private Const LOGPIXELSX = 88 Private Const LOGPIXELSY = 90 ' Converts twips corrdinates to pixels coordinates Private Sub Twips2Pixels(X As Long, Y As Long) Dim hDC As Long hDC = GetDC(0) X = X / 1440 * GetDeviceCaps(hDC, LOGPIXELSX) Y = Y / 1440 * GetDeviceCaps(hDC, LOGPIXELSY) ReleaseDC 0, hDC End Sub

What should I do if my control is flickering ?

If you feel that a window is flickering while you are updating a control, you can use the showWindow function described bellow. The function hides the window, but do not reflect the changes ( in the container window ) until you show again the window. The function uses the SetWindowPos API function. There is a LockWindow API function, but it locks only a single window at a time.

' We need SetWindowPos API Private Declare Function SetWindowPos Lib "user32" (ByVal hwnd As Long, ByVal hWndInsertAfter As Long, ByVal x As Long, ByVal y As Long, ByVal cx As Long, ByVal cy As Long, ByVal wFlags As Long) As Long Private Const SWP_FRAMECHANGED = &H20 Private Const SWP_NOMOVE = &H2 Private Const SWP_NOREDRAW = &H8 Private Const SWP_NOSIZE = &H1 Private Const SWP_NOZORDER = &H4 Private Const SWP_SHOWWINDOW = &H40 Private Const SWP_HIDEWINDOW = &H80 Private Sub showWindow(ByVal h As Long, ByVal bShow As Boolean) If (Not bShow) Then SetWindowPos h, 0, 0, 0, 0, 0, SWP_NOSIZE Or SWP_NOMOVE Or SWP_NOZORDER Or SWP_HIDEWINDOW Or SWP_NOREDRAW Else SetWindowPos h, 0, 0, 0, 0, 0, SWP_NOSIZE Or SWP_NOMOVE Or SWP_NOZORDER Or SWP_SHOWWINDOW Or SWP_FRAMECHANGED End If End Sub Sample: showWindow List1.hwnd, False With List1 .BeginUpdate With .Items .Add "Item 1" .Add "Item 2" ............. .Add "Item n" End With .EndUpdate End With showWindow List1.hwnd, True

How to make your form semitransparent?

Using a layered window can significantly improve performance and visual effects for a window that has a complex shape, animates its shape, or wishes to use alpha blending effects:

Private Declare Function SetLayeredWindowAttributes Lib "user32.dll" (ByVal hwnd As Long, ByVal crKey As Long, ByVal bAlpha As Byte, ByVal dwFlags As Long) As Boolean Private Declare Function SetWindowLong Lib "user32" Alias "SetWindowLongA" (ByVal hwnd As Long, ByVal nIndex As Long, ByVal dwNewLong As Long) As Long Private Declare Function GetWindowLong Lib "user32" Alias "GetWindowLongA" (ByVal hwnd As Long, ByVal nIndex As Long) As Long Const LWA_ALPHA = 2 Const GWL_EXSTYLE = (-20) Const WS_EX_LAYERED = &H80000 Private Sub Form_Load() SetWindowLong hwnd, GWL_EXSTYLE, GetWindowLong(hwnd, GWL_EXSTYLE) Or WS_EX_LAYERED SetLayeredWindowAttributes hwnd, 0, 128, LWA_ALPHA End Sub

How can I get the list of processes?

The following sample runs un Windows NT, 2000 or XP. The sample prints each process and its modules:

Option Explicit Private Declare Function EnumProcesses Lib "psapi" (lpIdProcess As Any, ByVal cb As Long, cbNeeded As Long) As Long Private Declare Function EnumProcessModules Lib "psapi.dll" (ByVal hProcess As Long, ByRef lphModule As Long, ByVal cb As Long, ByRef cbNeeded As Long) As Long Private Declare Function OpenProcess Lib "kernel32" (ByVal dwDesiredAccess As Long, ByVal bInheritHandle As Long, ByVal dwProcessId As Long) As Long Private Declare Function GetModuleFileNameExA Lib "psapi.dll" (ByVal hProcess As Long, ByVal hModule As Long, ByVal ModuleName As String, ByVal nSize As Long) As Long Private Declare Function CloseHandle Lib "kernel32" (ByVal hObject As Long) As Long Private Const PROCESS_QUERY_INFORMATION = 1024 Private Const PROCESS_VM_READ = 16 Private Sub Form_Load() EnumP End Sub Private Function onEnumM(ByVal strModule As String, ByVal asProcess As Boolean) As Boolean onEnumM = True If (Not asProcess) Then strModule = " " & strModule End If Debug.Print strModule End Function Private Function EnumP() As Boolean Dim idProcess() As Long Dim cb As Long, I As Long cb = 16 Do ReDim idProcess(0 To cb - 1) As Long If EnumProcesses(idProcess(0), cb * 4, I) = 0 Then Exit Function If I < cb * 4 Then ReDim idProcess(0 To (I / 4) - 1) As Long EnumProcesses idProcess(0), cb * 4, I Exit Do End If cb = cb * 2 Loop Dim bResult As Boolean bResult = True For I = LBound(idProcess) To UBound(idProcess) Dim h As Long h = OpenProcess(PROCESS_QUERY_INFORMATION Or PROCESS_VM_READ, 0, idProcess(I)) If (h <> 0) Then bResult = EnumM(h) CloseHandle h If (Not bResult) Then Exit For End If Next EnumP = bResult End Function Private Function EnumM(ByVal hProcess As Long) As Boolean Dim hModule() As Long Dim cb As Long, I As Long ' If the cb is grather than 1 the procedure gets all modules of the process cb = 2 Do ReDim hModule(0 To cb - 1) As Long If EnumProcessModules(hProcess, hModule(0), cb * 4, I) = 0 Then EnumM = True Exit Function End If If (cb = 1) Then Exit Do If I < cb * 4 Then ReDim hModule(0 To (I / 4) - 1) As Long EnumProcessModules hProcess, hModule(0), cb * 4, I Exit Do End If cb = cb * 2 Loop For I = LBound(hModule) To UBound(hModule) Dim s As String s = String(1024, " ") s = Mid(s, 1, GetModuleFileNameExA(hProcess, hModule(I), s, 1024)) If (Not onEnumM(s, I = LBound(hModule))) Then EnumM = False Exit Function End If Next EnumM = True End Function

How can I display a files/folder view explorer to my form?

The following sample displays the "My Computer" view:

Private Sub Form_Load() Dim b As Object Set b = Controls.Add("Shell.Explorer", "Browser", Me) b.Object.Navigate2 "::{20D04FE0-3AEA-1069-A2D8-08002B30309D}" b.Visible = True End Sub

C++

I am looking for a tool that counts the number of lines in my project?

If you don't find anywhere a tool to do that, you can use this tool. It includes the source code too. It's MFC based, but it's easy and free. All that you need to do is to run the "lines.exe" file and to drag files/folders to the right-side list box control. If you drag a folder the control enumerates all files recursively. Change the extension masks to count only the files that you are interested into. Click here to download the lines project.

How do I get the file version entry in the resource?

The following function loads the RT_VERSION data and looks for the file version::

STDMETHODIMP get_Version(BSTR *pVal) { if ( pVal ) { *pVal = NULL; if ( HRSRC hVersion = FindResource( _Module.GetResourceInstance(), MAKEINTRESOURCE(VS_VERSION_INFO), RT_VERSION ) ) if ( HGLOBAL hGlobal = LoadResource( _Module.GetResourceInstance(), hVersion ) ) { WORD* pVersionInfo = (WORD*)LockResource( hGlobal ); DWORD* p = (DWORD*)pVersionInfo; // Looks for the Value signature: 0xFEEF04BD for ( int i = 0; i < (*pVersionInfo) / 2; i++, p++ ) if ( *p == 0xFEEF04BD ) { // Jumps the signature and the structure version fields. p += 2; DWORD dwMS = *p++, dwLS = *p; TCHAR szVersion[1024] = _T(""); wsprintf( szVersion, "%i.%i.%i.%i", HIWORD( dwMS ), LOWORD(dwMS), HIWORD( dwLS ), LOWORD( dwLS ) ); *pVal = A2BSTR( szVersion ); break; } UnlockResource( hGlobal ); FreeResource( hGlobal ); } return S_OK; } return E_POINTER; }

Fills a rectangle using a transparent color.

The following function fills a rectangle using a transparent color :

void FillRectTransparent( HDC hDC, RECT rtClient, COLORREF rgbColor ) { if ( HDC hDCMem = CreateCompatibleDC( hDC ) ) { long cx = rtClient.right - rtClient.left, cy = rtClient.bottom - rtClient.top; RECT rtMemClient = rtClient; OffsetRect( &rtMemClient, -rtClient.left, -rtClient.top ); if ( HBITMAP hBitmap = CreateCompatibleBitmap( hDC, cx, cy ) ) { CGDIBrush brush( rgbColor ); HBITMAP hOldBitmap = (HBITMAP)::SelectObject( hDCMem, hBitmap ); FillRect( hDCMem, &rtMemClient, brush.m_hBrush ); BitBlt( hDC, rtClient.left, rtClient.top, cx, cy, hDCMem, 0, 0, SRCAND ); ::SelectObject( hDCMem, hOldBitmap ); DeleteObject( hBitmap ); } DeleteDC( hDCMem ); } }

How do I create a shortcut file by code?

The following sample uses the IShellLink interface to create a shortcut file:

TCHAR* szShortCut = _T("c:\winnt\\calc.exe"); string strLinkFile = _T("c:\\temp\\calc.lnk"); CComPtr<IShellLink> spShellLink; CoInitialize( NULL ); if ( SUCCEEDED( CoCreateInstance( CLSID_ShellLink, NULL, CLSCTX_INPROC_SERVER, IID_IShellLink, (void**)&spShellLink ) ) ) { spShellLink->SetPath( szShortCut ); if ( CComQIPtr<IPersistFile> spFile(spShellLink) ) { USES_CONVERSION; spFile->Save( T2OLE(strLinkFile.c_str()), TRUE ); } } CoUninitialize();

How do I move my dialog without clicking in the caption area?

The following samples show how to let user moves the dialog by clicking anywhere in the dialog:

void CXdDlg::OnLButtonDown(UINT nFlags, CPoint point) { PostMessage( WM_NCLBUTTONDOWN, HTCAPTION, NULL ); CDialog::OnLButtonDown(nFlags, point); } void CXdDlg::OnLButtonDown(UINT nFlags, CPoint point) { PostMessage( WM_SYSCOMMAND, SC_MOVE , NULL ); CDialog::OnLButtonDown(nFlags, point); }

How to change the dialog's background?

You can handle the WM_ERASEBKGND or WM_CTLCOLORDLG message:

... MESSAGE_HANDLER(WM_CTLCOLORDLG, OnCtlColorDlg) ... LRESULT OnCtlColorDlg(UINT uMsg, WPARAM wParam, LPARAM lParam, BOOL& bHandled) { return (LRESULT)GetSysColorBrush( COLOR_WINDOW ); } ... MESSAGE_HANDLER(WM_ERASEBKGND, OnEraseBkGnd) ... LRESULT OnEraseBkGnd(UINT uMsg, WPARAM wParam, LPARAM lParam, BOOL& bHandled) { HDC hDC = (HDC)wParam; RECT rtClient = {0}; GetClipBox( hDC, &rtClient ); FillRect( hDC, &rtClient, GetSysColorBrush( COLOR_WINDOW )) ; return TRUE; }

How to convert a VARIANT to a string?

The VariantChangeType API function converts a VARIANT from one type to another. The following sample uses CComVariant class to convert a VARIANT to a string:

static string V2S( VARIANT* pv, LPCTSTR szDefault = _T("") ) { if ( pv ) { if ( pv->vt == VT_ERROR ) return szDefault; CComVariant vt; if ( SUCCEEDED( vt.ChangeType( VT_BSTR, pv ) ) ) { USES_CONVERSION; return OLE2T(V_BSTR( &vt )); } } return szDefault; }

How to find the name for interfaces that a COM object implements?

To find out the interfaces that a COM object implements, you have to query the object for all registered interfaces. The windows registry holds all known interfaces in the HKCR\Interfaces registry key. The QI::MsgBox( yourCOMObject ) displays a list of interfaces implemented by the passed object :

#include <atlbase.h> #include <string> #include <sstream> class QI : protected CRegKey, #ifdef _UNICODE public std::wstringstream #else public std::stringstream #endif { protected: virtual tstring Query( IUnknown* pUnk ) { if ( pUnk != NULL && ( ERROR_SUCCESS == Open( HKEY_CLASSES_ROOT, _T("Interface") ) ) ) { TCHAR szKeyName[1024] = _T(""); for ( int i = 0; ERROR_SUCCESS == RegEnumKey( m_hKey, i, szKeyName, 1024 ); i++ ) { USES_CONVERSION; CLSID clsID = CLSID_NULL; if ( SUCCEEDED( CLSIDFromString( T2OLE(szKeyName), &clsID ) ) ) { CComPtr<IUnknown> spObject = NULL; if ( SUCCEEDED( pUnk->QueryInterface( clsID, (void**)&spObject ) ) ) { TCHAR szValue[1024] = _T(""); LONG ncbValue = 1024; if ( ERROR_SUCCESS == RegQueryValue( m_hKey, szKeyName, szValue, &ncbValue ) ) *this << tstring(szValue) + _T("\r\n"); } } } Close(); } return str(); } public: static void MsgBox( IUnknown* pUnk ) { QI objQI; MessageBox( NULL, objQI.Query( pUnk ).c_str(), _T("The object implements:"), MB_ICONINFORMATION ); } };

I have a picture file, and all that I need is an object that handles that picture. What can I do?

A picture object implements this interface along with IPicture to provide access to the picture's properties through Automation. The following function loads a picture for a file:

BOOL LoadPicture( LPCTSTR szFileName, IPictureDisp** ppPictureDisp ) { BOOL bResult = FALSE; if ( szFileName ) { OFSTRUCT of; HANDLE hFile = NULL;; #ifdef _UNICODE USES_CONVERSION; if ( (hFile = (HANDLE)OpenFile( W2A(szFileName), &of, OF_READ | OF_SHARE_COMPAT)) != (HANDLE)HFILE_ERROR ) #else if ( (hFile = (HANDLE)OpenFile( szFileName, &of, OF_READ | OF_SHARE_COMPAT)) != (HANDLE)HFILE_ERROR ) #endif { *ppPictureDisp = NULL; DWORD dwHighWord = NULL, dwSizeLow = GetFileSize( hFile, &dwHighWord ); DWORD dwFileSize = dwSizeLow; HRESULT hResult = NULL; if ( HGLOBAL hGlobal = GlobalAlloc(GMEM_MOVEABLE, dwFileSize) ) if ( void* pvData = GlobalLock( hGlobal ) ) { DWORD dwReadBytes = NULL; BOOL bRead = ReadFile( hFile, pvData, dwFileSize, &dwReadBytes, NULL ); GlobalUnlock( hGlobal ); if ( bRead ) { CComPtr spStream; _ASSERTE( dwFileSize == dwReadBytes ); if ( SUCCEEDED( CreateStreamOnHGlobal( hGlobal, TRUE, &spStream) ) ) if ( SUCCEEDED( hResult = OleLoadPicture( spStream, 0, FALSE, IID_IPictureDisp, (void**)ppPictureDisp ) ) ) bResult = TRUE; } } CloseHandle( hFile ); } } return bResult; }

How can I load a picture from resource?

A picture object implements this interface along with IPicture to provide access to the picture's properties through Automation. The following function loads a picture for a application's resource:

ULONG CreateStream(const char *ResourceType, const char *ResourceName, IStream **ppStream) { BOOL bResult = FALSE; DWORD dwSize = NULL; #ifdef _ATL HMODULE hInstance = _Module.GetModuleInstance(); #else HMODULE hInstance = AfxGetResourceHandle(); #endif if ( HRSRC hResource = FindResource( hInstance, ResourceName, ResourceType ) ) if (HGLOBAL hGlobal = LoadResource( hInstance, hResource )) { if ( HGLOBAL hGlobalStream = GlobalAlloc(GMEM_MOVEABLE, dwSize = SizeofResource( hInstance, hResource ) ) ) { memcpy( GlobalLock( hGlobalStream ), LockResource( hGlobal ), dwSize ); GlobalUnlock( hGlobalStream ); if ( SUCCEEDED( CreateStreamOnHGlobal( hGlobalStream, TRUE, ppStream ) ) ) bResult = TRUE; } FreeResource( hResource ); } return bResult ? dwSize : 0; } IStream* pStream = NULL; if ( CreateStream( "JPG", MAKEINTRESOURCE( IDR_EXONTROL ), &pStream ) ) { IPictureDisp* pPictureDisp = NULL; if ( SUCCEEDED( OleLoadPicture( pStream, NULL, FALSE, IID_IPictureDisp, (LPVOID*)&pPictureDisp ) ) ) { ......................... pPictureDisp->Release(); } pStream->Release(); }

I have a IPictureDisp pointer, and want to draw the picture to a device context.

The DrawPicture method takes a IPictureDisp pointer, and paints the picture to give device context :

void DrawPicture( IPictureDisp* pPictureDisp, HDC hDC, RECT rDraw ) { if ( CComQIPtr<spPicture>( pPictureDisp ) ) { SIZEL src = {0,0}, srcExtent = { NULL, NULL }; spPicture->get_Width( (OLE_XSIZE_HIMETRIC*)&srcExtent.cx ) ; spPicture->get_Height( (OLE_YSIZE_HIMETRIC*)&srcExtent.cy ); SIZEL extent = srcExtent; AtlHiMetricToPixel( &srcExtent, &extent ); spPicture->Render( hDC, rDraw.left, rDraw.top, RectWidth(&rDraw), RectHeight(&rDraw), src.cx , srcExtent.cy - src.cy, srcExtent.cx, -srcExtent.cy, NULL ); } }

I have a bitmap and I want to draw it using a transparent color.

The following two functions helps you to draw a bitmap using a transparent color.

void BitBltTransparent( HDC hdcDest, int nXDest, int nYDest, int nWidth, int nHeight, HDC hdcSrc, int nXSrc, int nYSrc, COLORREF colorTransaparent) { if (HDC hdcMask = ::CreateCompatibleDC(hdcDest)) { HBITMAP hBitmap = CreateBitmap( nWidth, nHeight, 1, 1, NULL ); HBITMAP hdcMaskBitmap = (HBITMAP)::SelectObject( hdcMask, hBitmap ); ::SetBkColor( hdcSrc, colorTransaparent ); ::BitBlt( hdcMask, 0, 0, nWidth, nHeight, hdcSrc, nXSrc, nYSrc, SRCCOPY); ::SetBkColor( hdcSrc, NULL ); ::SetTextColor( hdcSrc, RGB(255,255,255) ); ::BitBlt( hdcSrc, nXSrc, nYSrc, nWidth, nHeight, hdcMask, 0,0, SRCAND ); ::SetBkColor( hdcDest, RGB(255,255,255) ); ::SetTextColor( hdcDest, NULL ); ::BitBlt( hdcDest, nXDest, nYDest, nWidth, nHeight, hdcMask, 0,0, SRCAND ); ::BitBlt(hdcDest, nXDest, nYDest, nWidth, nHeight, hdcSrc, nXSrc, nYSrc, SRCPAINT); ::SelectObject( hdcMask, hdcMaskBitmap ); DeleteDC( hdcMask ); DeleteObject( hBitmap ); } }; void BitBltTransparent( HDC hdcDest, int nXDest, int nYDest, int nWidth, int nHeight, HBITMAP hBitmap, int nXSrc, int nYSrc, COLORREF colorTransaparent ) { if ( hBitmap ) { HDC hDCBitmap = CreateCompatibleDC( hdcDest ); HBITMAP hOldBitmap = (HBITMAP)::SelectObject( hDCBitmap, hBitmap ); HDC hdcCopy = CreateCompatibleDC( hdcDest ); HBITMAP hBitmapCopy = CreateCompatibleBitmap( hdcDest, nWidth, nHeight ); HBITMAP hBitmapCopy2 = (HBITMAP)::SelectObject( hdcCopy, hBitmapCopy ); ::BitBlt( hdcCopy, 0, 0, nWidth, nHeight, hDCBitmap, nXSrc, nYSrc, SRCCOPY ); BitBltTransparent( hdcDest, nXDest, nYDest, nWidth, nHeight, hdcCopy, 0, 0, colorTransaparent ); ::SelectObject( hdcCopy, hBitmapCopy2 ); ::SelectObject( hDCBitmap, hOldBitmap ); ::DeleteObject( hBitmapCopy ); ::DeleteDC( hdcCopy ); ::DeleteDC( hDCBitmap ); } }

I don't want to use AtlAxCreateWindow, AtlAxCreateWindow2 in order to host my control ,because these are implemented in ATL.DLL file.

Here's the definition for CAxWnd window that implements a lite but powerful container that hosts a control using IClassFactory or IClassFactory2 interfaces.

class CAxWnd : public IDispatch, public IOleClientSite, public IOleInPlaceSite, public IOleInPlaceFrame, public CWindowImpl { public: typedef void (CALLBACK *ONEVENT)( LPARAM lParam, DISPID event, DISPPARAMS* pParameters ); class CAxEvents : public IDispatch { public: CAxEvents(CAxWnd* pWnd) : m_pWnd( pWnd ) { m_dwRef = 0; // reset the counter }; virtual ~CAxEvents() { }; // IUnknown STDMETHOD(QueryInterface)( REFIID riid, void* *ppvObject); STDMETHOD_(ULONG, AddRef)( void ); STDMETHOD_(ULONG, Release)( void ); // IDispacth STDMETHOD(GetTypeInfoCount)( UINT * pctinfo); STDMETHOD(GetTypeInfo)( UINT iTInfo, LCID lcid, ITypeInfo* *ppTInfo); STDMETHOD(GetIDsOfNames)( REFIID riid, LPOLESTR *rgszNames, UINT cNames, LCID lcid, DISPID *rgDispId ); STDMETHOD(Invoke)( DISPID dispIdMember, REFIID riid, LCID lcid, WORD wFlags, DISPPARAMS *pDispParams, VARIANT *pVarResult, EXCEPINFO *pExcepInfo, UINT *puArgErr); protected: // Attributes CAxWnd* m_pWnd; ULONG m_dwRef; }; protected: CAxWnd( ONEVENT onEvent = NULL, LPARAM lParam = NULL ); virtual ~CAxWnd(); public: DECLARE_WND_CLASS( _T("AxWnd") ) BEGIN_MSG_MAP(CAxWnd) MESSAGE_HANDLER(WM_CREATE, onCreate) MESSAGE_HANDLER(WM_DESTROY, onDestroy) MESSAGE_HANDLER(WM_SIZE, onSize) END_MSG_MAP() //IUnknown STDMETHOD(QueryInterface)( REFIID riid, void* *ppvObject ); STDMETHOD_(ULONG,AddRef)(void); STDMETHOD_(ULONG,Release)(void); // IDispatch STDMETHOD(GetTypeInfoCount)( UINT * pctinfo); STDMETHOD(GetTypeInfo)( UINT iTInfo, LCID lcid, ITypeInfo* *ppTInfo); STDMETHOD(GetIDsOfNames)( REFIID riid, LPOLESTR *rgszNames, UINT cNames, LCID lcid, DISPID *rgDispId); STDMETHOD(Invoke)( DISPID dispIdMember, REFIID riid, LCID lcid, WORD wFlags, DISPPARAMS *pDispParams, VARIANT *pVarResult, EXCEPINFO *pExcepInfo, UINT *puArgErr); //IOleClientSite STDMETHOD(SaveObject)( void ); STDMETHOD(GetMoniker)( DWORD dwAssign, DWORD dwWhichMoniker, IMoniker * *ppmk); STDMETHOD(GetContainer)( IOleContainer** ppContainer); STDMETHOD(ShowObject)( void ); STDMETHOD(OnShowWindow)( BOOL fShow); STDMETHOD(RequestNewObjectLayout)( void ); //IOleInPlaceSite STDMETHOD(CanInPlaceActivate)(void); STDMETHOD(OnInPlaceActivate)(void); STDMETHOD(OnUIActivate)(void); STDMETHOD(GetWindowContext)( IOleInPlaceFrame* *ppFrame, IOleInPlaceUIWindow* *ppDoc, LPRECT lprcPosRect, LPRECT lprcClipRect, LPOLEINPLACEFRAMEINFO lpFrameInfo); STDMETHOD(Scroll)( SIZE scrollExtant); STDMETHOD(OnUIDeactivate)( BOOL fUndoable); STDMETHOD(OnInPlaceDeactivate)(void); STDMETHOD(DiscardUndoState)(void); STDMETHOD(DeactivateAndUndo)(void ); STDMETHOD(OnPosRectChange)( LPCRECT lprcPosRect ); //IOleInPlaceUIWindow STDMETHOD(GetBorder)( LPRECT lprectBorder); STDMETHOD(RequestBorderSpace)( LPCBORDERWIDTHS pborderwidths); STDMETHOD(SetBorderSpace)( LPCBORDERWIDTHS pborderwidths); STDMETHOD(SetActiveObject)( IOleInPlaceActiveObject* pActiveObject, LPCOLESTR pszObjName); //IOleInPlaceFrame STDMETHOD(InsertMenus)( HMENU hmenuShared, LPOLEMENUGROUPWIDTHS lpMenuWidths); STDMETHOD(SetMenu)( HMENU hmenuShared, HOLEMENU holemenu, HWND hwndActiveObject); STDMETHOD(RemoveMenus)( HMENU hmenuShared); STDMETHOD(SetStatusText)( LPCOLESTR pszStatusText); STDMETHOD(EnableModeless)( BOOL fEnable); STDMETHOD(TranslateAccelerator)( LPMSG lpmsg, WORD wID); //IOleWindow STDMETHOD(GetWindow)( HWND* phwnd); STDMETHOD(ContextSensitiveHelp)( BOOL fEnterMode); public: // Operations static HRESULT AxCreateControl( HWND hWndParent, RECT rtPos, BSTR strProgID, BSTR strLicense = NULL, LPARAM lParam = NULL, ONEVENT onEvent = NULL, CAxWnd** ppAxWnd = NULL ); virtual IDispatch* GetControl(); // Attributes GUID m_iidEvent; ONEVENT m_onEvent; LPARAM m_lParam; protected: // Message handlers virtual void show(); virtual void hide(); virtual LRESULT onCreate(UINT uMsg, WPARAM wParam, LPARAM lParam, BOOL& bHandled); virtual LRESULT onDestroy(UINT uMsg, WPARAM wParam, LPARAM lParam, BOOL& bHandled); virtual LRESULT onSize(UINT uMsg, WPARAM wParam, LPARAM lParam, BOOL& bHandled); virtual void OnFinalMessage(HWND /*hWnd*/); virtual void term(); virtual void initEvents(); virtual void termEvents(); virtual HRESULT init( BSTR strProgID, BSTR strLicense ); static GUID iidEvents( IOleObject* pOleObject ); // Attributes CComBSTR m_strProgID; CComBSTR m_strLicense; CComPtr m_spControl; CComPtr m_spOleObject; int m_dwRef; BOOL m_bVisible; unsigned long m_dwObjectStatus; RECT m_rcPos; CAxEvents* m_pAxEvents; DWORD m_dwCookie; static int m_nInstances; };

Why the Invalidate method doesn't refresh my window, right after calling?

The invalidated areas accumulate in the update region until the region is processed when the next WM_PAINT message occurs or until the region is validated by using the ValidateRect function. The following function forces WM_PAINT message to be processed:

void WaitToValidate( HWND hWnd ) { MSG msg = {0}; while (::PeekMessage(&msg, NULL, WM_PAINT, WM_PAINT, PM_NOREMOVE)) { if (!GetMessage(&msg, NULL, WM_PAINT, WM_PAINT)) return; DispatchMessage(&msg); } }

I have a pointer and I want to know if it points to a valid memory area. What should I do ?

You can use the following function to check your pointer:

BOOL IsValidAddress(const void* lp, UINT nBytes, BOOL bReadWrite) { return (lp != NULL && !::IsBadReadPtr(lp, nBytes) && (!bReadWrite || !::IsBadWritePtr((LPVOID)lp, nBytes))); }

How CoCreateInstance works?

The CoCreateInstance creates a single uninitialized object of the class associated with a specified CLSID. The following sample takes the control's identifier and creates an object instance. The sample doesn't use CoCreateInstance method.

#include "stdafx.h" #include <windows.h> #include <atlbase.h> typedef HRESULT (CALLBACK *DLLGETCLASSOBJECT)(REFCLSID rclsid, REFIID riid, LPVOID* ppv); // Function name : MyCreateInstance // Description : Creates an object based on its identifier. // Return type : HRESULT // Argument : LPCTSTR szObjectID // Argument : IUnknown** ppObject HRESULT MyCreateInstance( LPCTSTR szObjectID, IUnknown** ppObject ) { HRESULT hResult = E_POINTER; if ( ppObject ) { *ppObject = NULL; USES_CONVERSION; CLSID clsid = CLSID_NULL; if ( SUCCEEDED( hResult = CLSIDFromProgID( T2OLE( szObjectID ), &clsid ) ) ) { BSTR strObjectCLSID = NULL; if ( SUCCEEDED( StringFromCLSID( clsid, &strObjectCLSID ) ) ) { TCHAR szModule[1024] = _T(""); TCHAR szInprocServer[1024] = _T(""); wsprintf( szInprocServer, _T("CLSID\\%s\\InprocServer32"), OLE2T( strObjectCLSID ) ); CRegKey key; if ( ERROR_SUCCESS == key.Open( HKEY_CLASSES_ROOT, szInprocServer , KEY_READ ) ) { DWORD dwCount = 1024; if ( ERROR_SUCCESS == key.QueryValue( szModule, _T(""), &dwCount ) ) { if ( HMODULE h = LoadLibrary( szModule ) ) { if ( DLLGETCLASSOBJECT s = (DLLGETCLASSOBJECT)GetProcAddress( h, "DllGetClassObject" ) ) { CComPtr<IClassFactory> spFactory; if ( SUCCEEDED( hResult = (s)( clsid, IID_IClassFactory, (LPVOID*) &spFactory ) ) ) hResult = spFactory->CreateInstance( NULL, IID_IUnknown, (LPVOID*)ppObject ); } FreeLibrary( h ); } } } CoTaskMemFree( strObjectCLSID ); } } } return hResult; } int main(int argc, char* argv[]) { CoInitialize( NULL ); CComPtr<IUnknown> spObject; HRESULT hResult = MyCreateInstance( _T("Exontrol.Grid"), &spObject ); CoUninitialize(); return 0; }

How can I retrieve the clipboard data?

The Clipboard2Variant method copies the content of the clipboard to a Variant.

// Function name : Clipboard2Variant // Description : Retrieves the content of Clipboard to the pvtValue // Return type : HRESULT // Argument : VARIANT* pvtValue HRESULT Clipboard2Variant( VARIANT* pvtValue ) { CComPtr<IDataObject> spDataObject; HRESULT hResult = E_POINTER; if ( pvtValue ) { USES_CONVERSION; VariantClear( pvtValue ); if ( SUCCEEDED( hResult = OleGetClipboard( &spDataObject ) ) ) { // We are looking for Text FORMATETC fetcText = { CF_TEXT, NULL, DVASPECT_CONTENT, -1, TYMED_HGLOBAL }; FORMATETC fetcObjectDescriptor = { cfObjectDescriptor, NULL, DVASPECT_CONTENT, -1, TYMED_HGLOBAL }; FORMATETC fetcEmbeddedObject = { cfEmbeddedObject, NULL, DVASPECT_CONTENT, -1, TYMED_ISTORAGE }; FORMATETC fetcEmbedSource = { cfEmbedSource, NULL, DVASPECT_CONTENT, -1, TYMED_ISTORAGE }; STGMEDIUM stgText; if ( !IsClipboardFormatAvailable( fetcObjectDescriptor.cfFormat ) ) if ( SUCCEEDED( hResult = spDataObject->GetData( &fetcText, &stgText ) ) ) { pvtValue->vt = VT_BSTR; pvtValue->bstrVal = ::SysAllocString( T2OLE( (LPTSTR)GlobalLock( stgText.hGlobal ) ) ); GlobalUnlock( stgText.hGlobal ); ReleaseStgMedium( &stgText ); return hResult; }; // We are looking for Object Descriptor STGMEDIUM stgObjectDescriptor; if ( SUCCEEDED( hResult = spDataObject->GetData( &fetcObjectDescriptor, &stgObjectDescriptor ) ) ) { HGLOBAL hGlobalObjectDescriptor = stgObjectDescriptor.hGlobal; if ( OBJECTDESCRIPTOR* pObjectDescriptor = (OBJECTDESCRIPTOR*)GlobalLock( hGlobalObjectDescriptor ) ) { BSTR bstrProgID = NULL; if ( SUCCEEDED( hResult = ProgIDFromCLSID( pObjectDescriptor->clsid, &bstrProgID ) ) ) { OLEObjectHeader oleObjectHeader; oleObjectHeader.strObjectClass = OLE2T(bstrProgID); oleObjectHeader.strObjectName = W2T((unsigned short*)((BYTE*)pObjectDescriptor + pObjectDescriptor->dwFullUserTypeName )); // We are looking for Object Storage; // There are two possibilties: Embed Source or Embedded Object. STGMEDIUM stgEmbed; if ( SUCCEEDED( hResult = spDataObject->GetData( &fetcEmbeddedObject, &stgEmbed ) ) || SUCCEEDED( hResult = spDataObject->GetData( &fetcEmbedSource, &stgEmbed ) ) ) { if ( LPMEMORYOLESTREAM pMemoryStream = CreateMemoryOleStream( NULL, NULL ) ) { oleObjectHeader.WriteToOLEStream( pMemoryStream ); OleConvertIStorageToOLESTREAM( stgEmbed.pstg, pMemoryStream ); SAFEARRAYBOUND safeArray = { GlobalSize( pMemoryStream->hGlobal ), 0 }; pvtValue->vt = VT_ARRAY | VT_UI1; pvtValue->parray = SafeArrayCreate( VT_UI1, 1, &safeArray ); void* pArrayData = NULL; if ( SUCCEEDED( hResult = SafeArrayAccessData( pvtValue->parray, &pArrayData ) ) ) { CopyMemory( pArrayData, GlobalLock( pMemoryStream->hGlobal ), safeArray.cElements ); GlobalUnlock( pMemoryStream->hGlobal ); SafeArrayUnaccessData( pvtValue->parray ); } DeleteMemoryOleStream( pMemoryStream ); } ReleaseStgMedium( &stgEmbed ); } CoTaskMemFree( bstrProgID ); }; }; GlobalUnlock( hGlobalObjectDescriptor ); ReleaseStgMedium( &stgObjectDescriptor ); }; }; } return hResult; }

Is there any equivalent function for VB Round function in C++?

The Round function performs round to even, which is different from round to larger. The return value is the number closest to the value of expression, with the appropriate number of decimal places. If expression is exactly halfway between two possible rounded values, the function returns the possible rounded value whose rightmost digit is an even number. (In a round to larger function, a number that is halfway between two possible rounded values is always rounded to the larger number.). Round to even is a statistically more accurate rounding algorithm than round to larger. A possible implementation for Round function can be found here:

long Round( double d ) { double f = floor( d ), c = ceil(d), df = d - f, cd = c - d; if ( df > cd ) return (long)c; if ( df < cd ) return (long)f; return (long)((long)f % 2 ? c : f); }

How can I have the Integer Division Operator "\" in my C++ program?

The "\" VB operator divides two numbers and returns an integer result. Before division is performed, numeric expressions are rounded to Byte, Integer, or Long subtype expressions. A possible implementation for "\" Integer Division Operator could be:

long( Round(d) / Round( n ) )

How do I load icons using more than 16 colors to my image list?

The LoadImage API function loads an icon, cursor, animated cursor, or bitmap. The LoadIcon API function loads the specified icon resource from the executable (.exe) file associated with an application instance. Both functions load icons with less than 16 colors. In order to load your icon file using more colors you have to use the LoadPicture function. The following code adds your icon to an image list using all colors in the icon:

CComPtr<IPictureDisp> spPictureDisp;
if ( LoadPicture( pszExeFileName, &spPictureDisp ) )
	if ( CComQIPtr<IPicture> spPicture(spPictureDisp) )
	{
		OLE_HANDLE hIcon = NULL;
		if ( SUCCEEDED( spPicture->get_Handle( &hIcon ) ) )
			ImageList_AddIcon( hImageList, (HICON)hIcon );
	}

How do I declare a pointer to a function in a C++ class (term does not evaluate to a function)?

Prototype the function with a complete argument list and then specify actual parameters when declaring the pointer, as follows:

type (*ptr)(parameter_list);

If the function you want to call is member of a class ( non static member ), you have to specify the prototype like:

type (class::*ptr)(parameter_list);

The following sample declares two classes A and B, and a pointer to a function that's not static:

class A
{

protected:
	void a1()
	{
		// do something
	}

	void a2()
	{
		// do something
	}
};

class B : public A
{
public:

	typedef void (A::*callback_a)();

	virtual void callA( callback_a a = A::a1 )
	{
		(this->*a)();
	}
};

If you would try to call in the function callA something like a(), or (*a)(), the compiler gives "error C2064: term does not evaluate to a function", that's why you have to call explicit the this pointer like: (this->*a)().

Saving EMF format to a picture file

The following function gets the EMF format from the clipboard and saves it to a picture file. You need a graphic viewer to view EMF files.

BOOL saveEMFtoFile( LPCTSTR szFileName )
{
	BOOL bResult = FALSE;
	if ( ::OpenClipboard( NULL ) )
	{
		CComPtr<IPicture> spPicture;
		PICTDESC pictDesc = {0};
		pictDesc.cbSizeofstruct = sizeof(pictDesc);
		pictDesc.emf.hemf = (HENHMETAFILE)GetClipboardData( CF_ENHMETAFILE );
		pictDesc.picType = PICTYPE_ENHMETAFILE;
		if ( SUCCEEDED( OleCreatePictureIndirect( &pictDesc, IID_IPicture, FALSE, (LPVOID*)&spPicture ) ) )
		{
			HGLOBAL hGlobal = NULL;
			CComPtr<IStream> spStream;
			if ( SUCCEEDED( CreateStreamOnHGlobal( hGlobal = GlobalAlloc( GPTR, 0 ), TRUE, &spStream ) ) )
			{
				long dwSize = NULL;
				if ( SUCCEEDED( spPicture->SaveAsFile( spStream, TRUE, &dwSize ) ) )
				{
					USES_CONVERSION;
					HANDLE hFile = CreateFile( szFileName, GENERIC_WRITE, NULL, NULL, CREATE_ALWAYS, NULL, NULL );
					if ( hFile != INVALID_HANDLE_VALUE )
					{
						LARGE_INTEGER l = {NULL};
						spStream->Seek(l, STREAM_SEEK_SET, NULL);
						long dwWritten = NULL;
						while ( dwWritten < dwSize )
						{
							unsigned long dwRead = NULL;
							BYTE b[10240] = {0};
							spStream->Read( &b, 10240, &dwRead );
							DWORD dwBWritten = NULL;
							WriteFile( hFile, b, dwRead, &dwBWritten, NULL );
							dwWritten += dwBWritten;
						}
						CloseHandle( hFile );
						bResult = TRUE;
					}
				}
			}
		}
		CloseClipboard();
	}
	return bResult;
}

How do I find the intersection of two rectangles?

The Windows system provides an API called IntersectRect. The IntersectRect function calculates the intersection of two source rectangles and places the coordinates of the intersection rectangle into the destination rectangle. If the source rectangles do not intersect, an empty rectangle (in which all coordinates are set to zero) is placed into the destination rectangle. The single problem with this API seems to be when one of the source rectangles is empty. An empty rectangle is when the width or height of the rectangle is 0. For instance, if you have a rectangle like (0,0,10,10) , and you want the intersection with (5,5,5,5) rectangle, the IntersectRect API gives (0,0,0,0), instead (5,5,5,5) that's actually not what we are looking for so the following function just gives you the correct intersection:

// Function name	: IntersectRectFix
// Description	    : The IntersectRect function calculates the intersection of two source rectangles and places the coordinates of the intersection rectangle into the destination rectangle.
// Return type		: RECT 
// Argument         : RECT* prtA
// Argument         : RECT* prtB
BOOL IntersectRectFix( RECT* prtResult, RECT* prtA, RECT* prtB )
{
	RECT rtEmpty = {0}, rtResult = rtEmpty;
	rtResult.left = min(max(prtA->left, prtB->left),prtB->right);
	rtResult.right = max(min(prtA->right, prtB->right),prtB->left);
	rtResult.top = min(max(prtA->top, prtB->top),prtB->bottom);
	rtResult.bottom = max(min(prtA->bottom, prtB->bottom),prtB->top);
	*prtResult = rtEmpty;
	RECT* p = prtA;
	for ( long i = 0; i < 2; i++, p = prtB )
		if ( !( ( ( rtResult.left >= p->left ) && ( rtResult.right <= p->right ) ) && ( ( rtResult.top >= p->top ) && ( rtResult.bottom <= p->bottom ) ) ) )
			return FALSE;
	*prtResult = rtResult;
	return TRUE;
}