使用 ADO 向数据库中存储一张图片

// 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);
    }
}