//存储图片
bool SaveImage(CImage *lpImg, _RecordsetPtr pRecordset, char* errormsg)
{
    //估算图像需要的内存大小，这里当作 BMP 格式来估算的，所以结果比实际需要的更大。
    SIZE_T buffersize = lpImg->GetWidth() * lpImg->GetHeight() * lpImg->GetBPP()/8 + sizeof(BITMAPINFO);
    HGLOBAL hMem = GlobalAlloc(GMEM_FIXED, buffersize);
    if(hMem != NULL)
    {
        IStream* pStream = NULL;
        CreateStreamOnHGlobal(hMem, FALSE, &pStream);
        if(pStream != NULL)
        {
            LARGE_INTEGER temp;
            ULARGE_INTEGER fileLength;
            temp.QuadPart = 0;

lpImg->Save(pStream); //写入内存流

//获取当前文件的位置
            pStream->Seek(temp, STREAM_SEEK_CUR, &fileLength);
            ULONG nLength = (ULONG)(fileLength.QuadPart+1);

SAFEARRAY* psa; 
            SAFEARRAYBOUND rgsabound[1]; 
            rgsabound[0].lLbound = 0; 
            rgsabound[0].cElements = nLength;

//VT_UI1 : Variable type is unsigned char. 
            psa = SafeArrayCreate(VT_UI1, 1, rgsabound);

//锁定内存
            BYTE *lpBytes = (BYTE*)GlobalLock(hMem);
            BYTE *lpTemp = lpBytes;
            for (LONG i = 0; i < nLength; i++) 
                SafeArrayPutElement (psa, &i, lpTemp++);
            //解锁内存
            GlobalUnlock(hMem);

VARIANT varBLOB;
            varBLOB.vt = VT_ARRAY | VT_UI1;
            varBLOB.parray = psa;

//存储
            pRecordset->Fields->GetItem("PHOTO")->AppendChunk(varBLOB);
            pStream->Release();

//
            SafeArrayDestroyData(psa);
        }
        else
        {
            GlobalFree(hMem);
            sprintf(errormsg, "CreateStreamOnHGlobal Failed");
            return false;
        }
        //释放全局内存
        GlobalFree(hMem);
    }
    else
    {
        sprintf(errormsg, "GlobalAlloc Failed!");
        return false;
    }
    return true;
}

//id：主键
void ReadImg(int id)
{
    _RecordsetPtr pRs = NULL; 
    _ConnectionPtr pConnection = NULL; 
    _variant_t varChunk; 
    HRESULT hr;

//连接字符串
    _bstr_t strCnn("Provider=SQLOLEDB;Server=...;Database=...;User ID=...;Password=...;"); 
    try
    {
        //Open a connection 
        pConnection.CreateInstance(__uuidof(Connection)); 
        hr = pConnection->Open(strCnn,"","",NULL); 
        pRs.CreateInstance(__uuidof(Recordset));

//表名略
        char cmdText[128];
        sprintf(cmdText, "select PHOTO from ... where ID = %d", id);

pRs->Open(cmdText,_variant_t((IDispatch *) pConnection,true),adOpenKeyset,adLockOptimistic,adCmdText); 
        //read data 
        long lPhotoSize = pRs->Fields->GetItem("PHOTO")->ActualSize; 
        long llsRead = 0;
        _variant_t varChunk;
        
        BYTE buf[ChunkSize];

printf("lDatalength = %ld\n", lPhotoSize);

//保存到C盘
        char filename[128];
        sprintf(filename, "C:\\ID_%d.jpg", id);
        FILE* stream = fopen(filename, "wb");

while(lPhotoSize > 0)
        {
            llsRead = lPhotoSize >= ChunkSize? ChunkSize:lPhotoSize;

varChunk = pRs->Fields->GetItem("PHOTO")->GetChunk(llsRead);

for(long index = 0; index < llsRead; index++)
            {
                SafeArrayGetElement(varChunk.parray, &index, buf+index);
            }

fwrite(buf, 1, llsRead, stream);
            lPhotoSize -= llsRead;
        }
        fclose(stream);

printf("Save File Complete: %s\n", filename);
        
        pRs->Close(); 
        pConnection->Close(); 
    }
    catch(_com_error &e) 
    { 
        // Notify the user of errors if any. 
        _bstr_t bstrSource(e.Source()); 
        _bstr_t bstrDescription(e.Description()); 
        CString sError; 
        sError.Format(_T("Source : %s \n Description : %s\n"),(LPCSTR)bstrSource,(LPCSTR)bstrDescription); 
        //AfxMessageBox(sError); 
        //printf("%s\n", sError);
    }
}