Default IStream Implementation

 

This example contains a default implementation of a class that implements the IStream interface. You can use this class in your programs to read and write streams for XmlLite.

This example works with Visual Studio 2005 and later.

FileStream Implementation

//implement filestream that derives from IStream  
class FileStream : public IStream  
{  
    FileStream(HANDLE hFile)   
    {  
        _refcount = 1;  
        _hFile = hFile;  
    }  
  
    ~FileStream()  
    {  
        if (_hFile != INVALID_HANDLE_VALUE)  
        {  
            ::CloseHandle(_hFile);  
        }  
    }  
  
public:  
    HRESULT static OpenFile(LPCWSTR pName, IStream ** ppStream, bool fWrite)  
    {  
        HANDLE hFile = ::CreateFileW(pName, fWrite ? GENERIC_WRITE : GENERIC_READ, FILE_SHARE_READ,  
            NULL, fWrite ? CREATE_ALWAYS : OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL);  
  
        if (hFile == INVALID_HANDLE_VALUE)  
            return HRESULT_FROM_WIN32(GetLastError());  
  
        *ppStream = new FileStream(hFile);  
  
        if(*ppStream == NULL)  
            CloseHandle(hFile);  
  
        return S_OK;  
    }  
  
    virtual HRESULT STDMETHODCALLTYPE QueryInterface(REFIID iid, void ** ppvObject)  
    {   
        if (iid == __uuidof(IUnknown)  
            || iid == __uuidof(IStream)  
            || iid == __uuidof(ISequentialStream))  
        {  
            *ppvObject = static_cast<IStream*>(this);  
            AddRef();  
            return S_OK;  
        } else  
            return E_NOINTERFACE;   
    }  
  
    virtual ULONG STDMETHODCALLTYPE AddRef(void)   
    {   
        return (ULONG)InterlockedIncrement(&_refcount);   
    }  
  
    virtual ULONG STDMETHODCALLTYPE Release(void)   
    {  
        ULONG res = (ULONG) InterlockedDecrement(&_refcount);  
        if (res == 0)   
            delete this;  
        return res;  
    }  
  
    // ISequentialStream Interface  
public:  
    virtual HRESULT STDMETHODCALLTYPE Read(void* pv, ULONG cb, ULONG* pcbRead)  
    {  
        BOOL rc = ReadFile(_hFile, pv, cb, pcbRead, NULL);  
        return (rc) ? S_OK : HRESULT_FROM_WIN32(GetLastError());  
    }  
  
    virtual HRESULT STDMETHODCALLTYPE Write(void const* pv, ULONG cb, ULONG* pcbWritten)  
    {  
        BOOL rc = WriteFile(_hFile, pv, cb, pcbWritten, NULL);  
        return rc ? S_OK : HRESULT_FROM_WIN32(GetLastError());  
    }  
  
    // IStream Interface  
public:  
    virtual HRESULT STDMETHODCALLTYPE SetSize(ULARGE_INTEGER)  
    {   
        return E_NOTIMPL;     
    }  
  
    virtual HRESULT STDMETHODCALLTYPE CopyTo(IStream*, ULARGE_INTEGER, ULARGE_INTEGER*,  
        ULARGE_INTEGER*)   
    {   
        return E_NOTIMPL;     
    }  
  
    virtual HRESULT STDMETHODCALLTYPE Commit(DWORD)                                        
    {   
        return E_NOTIMPL;     
    }  
  
    virtual HRESULT STDMETHODCALLTYPE Revert(void)                                         
    {   
        return E_NOTIMPL;     
    }  
  
    virtual HRESULT STDMETHODCALLTYPE LockRegion(ULARGE_INTEGER, ULARGE_INTEGER, DWORD)                
    {   
        return E_NOTIMPL;     
    }  
  
    virtual HRESULT STDMETHODCALLTYPE UnlockRegion(ULARGE_INTEGER, ULARGE_INTEGER, DWORD)              
    {   
        return E_NOTIMPL;     
    }  
  
    virtual HRESULT STDMETHODCALLTYPE Clone(IStream **)                                    
    {   
        return E_NOTIMPL;     
    }  
  
    virtual HRESULT STDMETHODCALLTYPE Seek(LARGE_INTEGER liDistanceToMove, DWORD dwOrigin,  
        ULARGE_INTEGER* lpNewFilePointer)  
    {   
        DWORD dwMoveMethod;  
  
        switch(dwOrigin)  
        {  
        case STREAM_SEEK_SET:  
            dwMoveMethod = FILE_BEGIN;  
            break;  
        case STREAM_SEEK_CUR:  
            dwMoveMethod = FILE_CURRENT;  
            break;  
        case STREAM_SEEK_END:  
            dwMoveMethod = FILE_END;  
            break;  
        default:     
            return STG_E_INVALIDFUNCTION;  
            break;  
        }  
  
        if (SetFilePointerEx(_hFile, liDistanceToMove, (PLARGE_INTEGER) lpNewFilePointer,  
                             dwMoveMethod) == 0)  
            return HRESULT_FROM_WIN32(GetLastError());  
        return S_OK;  
    }  
  
    virtual HRESULT STDMETHODCALLTYPE Stat(STATSTG* pStatstg, DWORD grfStatFlag)   
    {  
        if (GetFileSizeEx(_hFile, (PLARGE_INTEGER) &pStatstg->cbSize) == 0)  
            return HRESULT_FROM_WIN32(GetLastError());  
        return S_OK;  
    }  
  
private:  
    HANDLE _hFile;  
    LONG _refcount;  
};  

See Also

XmlLite Reader Programming Overview