C中使用Stream Object讀取數(shù)據(jù)中流文件并顯示Bmp,JPG等圖片
在VC中我們通常用Ado的Field 對(duì)象的GetChuck和AppendChunk來(lái)讀寫(xiě)B(tài)lob對(duì)象，但是這樣做要寫(xiě)很多的代碼，其實(shí)ado給我們提供了一個(gè)更易操作的對(duì)象那就是Stream Object，通過(guò)它我們可以更容易的操作數(shù)據(jù)庫(kù)中的Blob對(duì)象，而且可以直接把Blob對(duì)象從數(shù)據(jù)庫(kù)保存到本地文件，或者直接讀取文件寫(xiě)入到數(shù)據(jù)庫(kù)中。下面就詳細(xì)描述如何操作。
首先申明Stream對(duì)象
_ StreamPtr pStm;
pStm.CreateInstance( "ADODB.Stream ");
variant_t varOptional(DISP_E_PARAMNOTFOUND,VT_ERROR);
pStm-> PutType(adTypeBinary);//類(lèi)型為二進(jìn)制
//得到字段內(nèi)容的大小
// long lDataSize = m_pRecordset-> GetFields()-> GetItem( "photo ")-> ActualSize;
//m_pRecordset為一個(gè)打開(kāi)的紀(jì)錄集對(duì)象，含有photo這個(gè)blob字段
pStm-> Open( varOptional,
adModeUnknown, adOpenStreamUnspecified, _bstr_t(), _bstr_t());
//打開(kāi)pStm
pStm-> Write(_variant_t(m_pRecordset-> GetFields()-> GetItem( "photo ")-> Value));
//把photo字段的內(nèi)容寫(xiě)入pStm
pStm-> SaveToFile( "c:\\publogo.jpg ", adSaveCreateOverWrite);
pStm-> Close();
//直接保存為文件,如果是別的格式只要保存的時(shí)候改變后綴就可以了
下面是如果不保存成文件可以直接通過(guò)Com對(duì)象來(lái)繪制該圖片，IPicture 可以顯示多種格式圖片.
HGLOBAL hGlobal = GlobalAlloc(GMEM_MOVEABLE, pStm-> GetSize());
LPVOID pvData = NULL;
IStream *ps;
if (hGlobal != NULL)
{
if ((pvData = GlobalLock(hGlobal)) != NULL)
{
char * m_pBMPBuffer = new char[pStm-> GetSize()+1];//分配必要的存儲(chǔ)空間
char *pBuf = NULL;
SafeArrayAccessData(varBLOB.parray,(void **)&pBuf);
memcpy(pvData,pBuf,pStm-> GetSize()); //復(fù)制數(shù)據(jù)到緩沖 區(qū) m_pBMPBuffer
SafeArrayUnaccessData (varBLOB.parray);
GlobalUnlock(hGlobal);
CreateStreamOnHGlobal(hGlobal, TRUE, &ps);
}
}
IPicture *pPic;
if(SUCCEEDED(OleLoadPicture(ps,pStm-> GetSize() ,TRUE,IID_IPicture,(LPVOID*)&pPic)))
{
OLE_XSIZE_HIMETRIC hmWidth;
OLE_YSIZE_HIMETRIC hmHeight;
pPic-> get_Width(&hmWidth);
pPic-> get_Height(&hmHeight);
double fX,fY;
CDC *pDC = GetClientDC();//這里根據(jù)具體請(qǐng)況來(lái)取
fX=(double)pDC-> GetDeviceCaps(HORZRES)*(double)hmWidth/((double)pDC-> GetDeviceCaps(HORZSIZE)*100.0);
fY =(double)pDC-> GetDeviceCaps(VERTRES)*(double)hmHeight/((double)pDC-> GetDeviceCaps(VERTSIZE)*100.0);
if(FAILED(pPic-> Render(*pDC,0,0,(DWORD)fX,(DWORD)fY,0,hmHeight,hmWidth,-hmHeight,NULL)))
AfxMessageBox( "圖像繪制失敗！ ");
pPic-> Release();
}
這樣就完成了對(duì)圖片文件從數(shù)據(jù)庫(kù)讀出和顯示的過(guò)程。
對(duì)于從文件寫(xiě)入數(shù)據(jù)庫(kù)就相對(duì)的容易多了,
_StreamPtr pStm;
pStm.CreateInstance( "ADODB.Stream ");
variant_t varOptional(DISP_E_PARAMNOTFOUND,VT_ERROR);
// long lDataSize = m_pRecordset-> GetFields()-> GetItem( "photo ")-> ActualSize;
pStm-> PutType(adTypeBinary；
pStm-> Open( varOptional,
adModeUnknown, adOpenStreamUnspecified, _bstr_t(), _bstr_t());
pStm-> LoadFromFile( "c:\\book.gif ");//讀入文件
variant_t varBLOB=pStm-> Read(adReadAll);
m_pRecordset-> GetFields()-> GetItem( "photo ")-> Value= varBLOB;//保存到數(shù)據(jù)集對(duì)象。
以上就是關(guān)于ADO的Stream對(duì)象操作數(shù)據(jù)庫(kù)中的blob字段的具體方法，主要是對(duì)圖片我們還可對(duì)它進(jìn)行改造成其他的，比如讀者可以改造成讀取XMl文件，并保存等等。
轉(zhuǎn)換為Bitmap
CComPtr <IPicture> spPic;
if (varImage.vt != (VT_ARRAY|VT_UI1))return FALSE;
SAFEARRAY *psa = varImage.parray;
//get size
long size=0;
_com_util::CheckError(SafeArrayGetUBound(psa, 1, &size));
size += 1;
//copy
char *pBuf = NULL;
_com_util::CheckError(SafeArrayAccessData(psa, (void **)&pBuf));
HGLOBAL hGlobal = GlobalAlloc(GMEM_MOVEABLE, size);
void *pGlobal = GlobalLock(hGlobal);
if (!pGlobal)return FALSE;
memcpy(pGlobal, pBuf, size);
SafeArrayUnaccessData(psa);
GlobalUnlock(hGlobal);
CComPtr <IStream> spStream;
_com_util::CheckError(CreateStreamOnHGlobal(hGlobal, true, &spStream));
_com_util::CheckError(OleLoadPicture(spStream, 0, TRUE, IID_IPicture, (void **)&spPic));
HBITMAP hBmp;
spPic-> get_Handle((OLE_HANDLE *)&hBmp);
CBitmap bmp;
bmp.Attach(hBmp);
BITMAP bm;
bmp.GetBitmap(&bm);
int x=bm.bmWidth;
int y=bm.bmHeight;
bmp.Detach();
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